CLAUDE.md

@@ -26,6 +26,12 @@ Query Prometheus metrics, Alertmanager alerts, and Loki logs. Unlike other serve
 - 3 optional Loki tools (when `LOKI_URL` is set): query_logs, list_labels, list_label_values
 - Configurable Prometheus, Alertmanager, and Loki URLs via flags or environment variables
 
+### Git Explorer (`git-explorer`)
+Read-only access to git repository information. Designed for deployment verification.
+- 9 tools: resolve_ref, get_log, get_commit_info, get_diff_files, get_file_at_commit, is_ancestor, commits_between, list_branches, search_commits
+- Uses go-git library for pure Go implementation
+- All operations are read-only (never modifies repository)
+
 The nixpkgs/options/hm servers share a database-backed architecture:
 - Full-text search across option/package names and descriptions
 - Query specific options/packages with full metadata
@@ -62,8 +68,10 @@ labmcp/
 │   │   └── main.go             # NixOS options CLI (legacy)
 │   ├── hm-options/
 │   │   └── main.go             # Home Manager options CLI
-│   └── lab-monitoring/
+│   ├── lab-monitoring/
-│       └── main.go             # Prometheus/Alertmanager CLI
+│   │   └── main.go             # Prometheus/Alertmanager CLI
+│   └── git-explorer/
+│       └── main.go             # Git repository explorer CLI
 ├── internal/
 │   ├── database/
 │   │   ├── interface.go        # Store interface (options + packages)
@@ -96,18 +104,26 @@ labmcp/
 │   │   ├── parser.go           # nix-env JSON parsing
 │   │   ├── types.go            # Package types, channel aliases
 │   │   └── *_test.go           # Parser tests
-│   └── monitoring/
+│   ├── monitoring/
-│       ├── types.go            # Prometheus/Alertmanager/Loki API types
+│   │   ├── types.go            # Prometheus/Alertmanager/Loki API types
-│       ├── prometheus.go       # Prometheus HTTP client
+│   │   ├── prometheus.go       # Prometheus HTTP client
-│       ├── alertmanager.go     # Alertmanager HTTP client
+│   │   ├── alertmanager.go     # Alertmanager HTTP client
-│       ├── loki.go             # Loki HTTP client
+│   │   ├── loki.go             # Loki HTTP client
+│   │   ├── handlers.go         # MCP tool definitions + handlers
+│   │   ├── format.go           # Markdown formatting utilities
+│   │   └── *_test.go           # Tests (httptest-based)
+│   └── gitexplorer/
+│       ├── client.go           # go-git repository wrapper
+│       ├── types.go            # Type definitions
 │       ├── handlers.go         # MCP tool definitions + handlers
-│       ├── format.go           # Markdown formatting utilities
+│       ├── format.go           # Markdown formatters
-│       └── *_test.go           # Tests (httptest-based)
+│       ├── validation.go       # Path validation
+│       └── *_test.go           # Tests
 ├── nix/
 │   ├── module.nix                  # NixOS module for nixos-options
 │   ├── hm-options-module.nix       # NixOS module for hm-options
 │   ├── lab-monitoring-module.nix   # NixOS module for lab-monitoring
+│   ├── git-explorer-module.nix     # NixOS module for git-explorer
 │   └── package.nix                 # Parameterized Nix package
 ├── testdata/
 │   └── options-sample.json     # Test fixture
@@ -158,6 +174,20 @@ labmcp/
 | `list_labels` | List available label names from Loki (requires `LOKI_URL`) |
 | `list_label_values` | List values for a specific label from Loki (requires `LOKI_URL`) |
 
+### Git Explorer Server (git-explorer)
+
+| Tool | Description |
+|------|-------------|
+| `resolve_ref` | Resolve a git ref (branch, tag, commit) to its full commit hash |
+| `get_log` | Get commit log with optional filters (author, path, limit) |
+| `get_commit_info` | Get full details for a specific commit |
+| `get_diff_files` | Get list of files changed between two commits |
+| `get_file_at_commit` | Get file contents at a specific commit |
+| `is_ancestor` | Check if one commit is an ancestor of another |
+| `commits_between` | Get all commits between two refs |
+| `list_branches` | List all branches in the repository |
+| `search_commits` | Search commit messages for a pattern |
+
 ## Key Implementation Details
 
 ### Database
@@ -261,6 +291,20 @@ lab-monitoring labels                         # List Loki labels
 lab-monitoring labels --values job            # List values for a label
 ```
 
+### git-explorer
+```bash
+git-explorer serve                            # Run MCP server on STDIO
+git-explorer serve --transport http           # Run MCP server on HTTP
+git-explorer --repo /path resolve <ref>       # Resolve ref to commit hash
+git-explorer --repo /path log --limit 10      # Show commit log
+git-explorer --repo /path show <ref>          # Show commit details
+git-explorer --repo /path diff <from> <to>    # Files changed between commits
+git-explorer --repo /path cat <ref> <path>    # File contents at commit
+git-explorer --repo /path branches            # List branches
+git-explorer --repo /path search <query>      # Search commit messages
+git-explorer --version                        # Show version
+```
+
 ### Channel Aliases
 
 **nixpkgs-search/nixos-options**: `nixos-unstable`, `nixos-stable`, `nixos-24.11`, `nixos-24.05`, etc.
@@ -314,6 +358,7 @@ Each package's version is defined in multiple places that must stay in sync *for
 - **nixpkgs-search**: `cmd/nixpkgs-search/main.go` + `internal/mcp/server.go` (`DefaultNixOSConfig`, `DefaultNixpkgsPackagesConfig`)
 - **nixos-options**: `cmd/nixos-options/main.go` + `internal/mcp/server.go` (`DefaultNixOSConfig`)
 - **hm-options**: `cmd/hm-options/main.go` + `internal/mcp/server.go` (`DefaultHomeManagerConfig`)
+- **git-explorer**: `cmd/git-explorer/main.go` + `internal/mcp/server.go` (`DefaultGitExplorerConfig`)
 - **nix/package.nix**: Shared across all packages (bump to highest version when any package changes)
 
 ### User Preferences
@@ -341,6 +386,7 @@ nix build .#nixpkgs-search
 nix build .#nixos-options
 nix build .#hm-options
 nix build .#lab-monitoring
+nix build .#git-explorer
 
 # Run directly
 nix run .#nixpkgs-search -- options serve
@@ -349,6 +395,7 @@ nix run .#nixpkgs-search -- index nixos-unstable
 nix run .#hm-options -- serve
 nix run .#hm-options -- index hm-unstable
 nix run .#lab-monitoring -- serve
+nix run .#git-explorer -- --repo . serve
 ```
 
 ### Indexing Performance

README.md

@@ -27,6 +27,20 @@ Query Prometheus metrics, Alertmanager alerts, and Loki logs from your monitorin
 - Manage alert silences
 - Query logs via LogQL (when Loki is configured)
 
+### Git Explorer (`git-explorer`)
+
+Read-only access to git repository information. Designed for deployment verification — comparing deployed flake revisions against source repositories.
+
+- Resolve refs (branches, tags, commits) to commit hashes
+- View commit logs with filtering by author, path, or range
+- Get full commit details including file change statistics
+- Compare commits to see which files changed
+- Read file contents at any commit
+- Check ancestry relationships between commits
+- Search commit messages
+
+All operations are read-only and will never modify the repository.
+
 ### NixOS Options (`nixos-options`) - Legacy
 
 Search and query NixOS configuration options. **Note**: Prefer using `nixpkgs-search` instead, which includes this functionality plus package search.
@@ -48,11 +62,13 @@ Search and query NixOS configuration options. **Note**: Prefer using `nixpkgs-se
 nix build git+https://git.t-juice.club/torjus/labmcp#nixpkgs-search
 nix build git+https://git.t-juice.club/torjus/labmcp#hm-options
 nix build git+https://git.t-juice.club/torjus/labmcp#lab-monitoring
+nix build git+https://git.t-juice.club/torjus/labmcp#git-explorer
 
 # Or run directly
 nix run git+https://git.t-juice.club/torjus/labmcp#nixpkgs-search -- --help
 nix run git+https://git.t-juice.club/torjus/labmcp#hm-options -- --help
 nix run git+https://git.t-juice.club/torjus/labmcp#lab-monitoring -- --help
+nix run git+https://git.t-juice.club/torjus/labmcp#git-explorer -- --help
 ```
 
 ### From Source
@@ -61,6 +77,7 @@ nix run git+https://git.t-juice.club/torjus/labmcp#lab-monitoring -- --help
 go install git.t-juice.club/torjus/labmcp/cmd/nixpkgs-search@latest
 go install git.t-juice.club/torjus/labmcp/cmd/hm-options@latest
 go install git.t-juice.club/torjus/labmcp/cmd/lab-monitoring@latest
+go install git.t-juice.club/torjus/labmcp/cmd/git-explorer@latest
 ```
 
 ## Usage
@@ -101,6 +118,13 @@ Configure in your MCP client (e.g., Claude Desktop):
         "ALERTMANAGER_URL": "http://alertmanager.example.com:9093",
         "LOKI_URL": "http://loki.example.com:3100"
       }
+    },
+    "git-explorer": {
+      "command": "git-explorer",
+      "args": ["serve"],
+      "env": {
+        "GIT_REPO_PATH": "/path/to/your/repo"
+      }
     }
   }
 }
@@ -140,6 +164,13 @@ Alternatively, if you have Nix installed, you can use the flake directly without
         "ALERTMANAGER_URL": "http://alertmanager.example.com:9093",
         "LOKI_URL": "http://loki.example.com:3100"
       }
+    },
+    "git-explorer": {
+      "command": "nix",
+      "args": ["run", "git+https://git.t-juice.club/torjus/labmcp#git-explorer", "--", "serve"],
+      "env": {
+        "GIT_REPO_PATH": "/path/to/your/repo"
+      }
     }
   }
 }
@@ -155,6 +186,7 @@ nixpkgs-search options serve --transport http
 nixpkgs-search packages serve --transport http
 hm-options serve --transport http
 lab-monitoring serve --transport http
+git-explorer serve --transport http
 
 # Custom address and CORS configuration
 nixpkgs-search options serve --transport http \
@@ -271,6 +303,35 @@ lab-monitoring labels
 lab-monitoring labels --values job
 ```
 
+**Git Explorer CLI:**
+
+```bash
+# Resolve a ref to commit hash
+git-explorer --repo /path/to/repo resolve main
+git-explorer --repo /path/to/repo resolve v1.0.0
+
+# View commit log
+git-explorer --repo /path/to/repo log --limit 10
+git-explorer --repo /path/to/repo log --author "John" --path src/
+
+# Show commit details
+git-explorer --repo /path/to/repo show HEAD
+git-explorer --repo /path/to/repo show abc1234
+
+# Compare commits
+git-explorer --repo /path/to/repo diff HEAD~5 HEAD
+
+# Show file at specific commit
+git-explorer --repo /path/to/repo cat HEAD README.md
+
+# List branches
+git-explorer --repo /path/to/repo branches
+git-explorer --repo /path/to/repo branches --remote
+
+# Search commit messages
+git-explorer --repo /path/to/repo search "fix bug"
+```
+
 **Delete an indexed revision:**
 
 ```bash
@@ -354,6 +415,20 @@ hm-options -d "sqlite://my.db" index hm-unstable
 | `list_labels` | List available label names from Loki (requires `LOKI_URL`) |
 | `list_label_values` | List values for a specific label from Loki (requires `LOKI_URL`) |
 
+### Git Explorer Server (git-explorer)
+
+| Tool | Description |
+|------|-------------|
+| `resolve_ref` | Resolve a git ref (branch, tag, commit) to its full commit hash |
+| `get_log` | Get commit log with optional filters (author, path, limit) |
+| `get_commit_info` | Get full details for a specific commit |
+| `get_diff_files` | Get list of files changed between two commits |
+| `get_file_at_commit` | Get file contents at a specific commit |
+| `is_ancestor` | Check if one commit is an ancestor of another |
+| `commits_between` | Get all commits between two refs |
+| `list_branches` | List all branches in the repository |
+| `search_commits` | Search commit messages for a pattern |
+
 ## NixOS Modules
 
 NixOS modules are provided for running the MCP servers as systemd services.
@@ -445,6 +520,29 @@ The `nixpkgs-search` module runs two separate MCP servers (options and packages)
 }
 ```
 
+### git-explorer
+
+```nix
+{
+  inputs.labmcp.url = "git+https://git.t-juice.club/torjus/labmcp";
+
+  outputs = { self, nixpkgs, labmcp }: {
+    nixosConfigurations.myhost = nixpkgs.lib.nixosSystem {
+      system = "x86_64-linux";
+      modules = [
+        labmcp.nixosModules.git-explorer-mcp
+        {
+          services.git-explorer = {
+            enable = true;
+            repoPath = "/path/to/your/git/repo";
+          };
+        }
+      ];
+    };
+  };
+}
+```
+
 ### nixos-options (Legacy)
 
 ```nix
@@ -519,6 +617,25 @@ Both `options.http` and `packages.http` also support:
 
 The lab-monitoring module uses `DynamicUser=true`, so no separate user/group configuration is needed.
 
+#### git-explorer
+
+| Option | Type | Default | Description |
+|--------|------|---------|-------------|
+| `enable` | bool | `false` | Enable the service |
+| `package` | package | from flake | Package to use |
+| `repoPath` | string | *(required)* | Path to the git repository to serve |
+| `defaultRemote` | string | `"origin"` | Default remote name for ref resolution |
+| `http.address` | string | `"127.0.0.1:8085"` | HTTP listen address |
+| `http.endpoint` | string | `"/mcp"` | HTTP endpoint path |
+| `http.allowedOrigins` | list of string | `[]` | Allowed CORS origins |
+| `http.sessionTTL` | string | `"30m"` | Session timeout |
+| `http.tls.enable` | bool | `false` | Enable TLS |
+| `http.tls.certFile` | path | `null` | TLS certificate file |
+| `http.tls.keyFile` | path | `null` | TLS private key file |
+| `openFirewall` | bool | `false` | Open firewall for HTTP port |
+
+The git-explorer module uses `DynamicUser=true` and grants read-only access to the repository path.
+
 #### hm-options-mcp / nixos-options-mcp (Legacy)
 
 | Option | Type | Default | Description |
@@ -579,6 +696,7 @@ go test -bench=. ./internal/database/...
 go build ./cmd/nixpkgs-search
 go build ./cmd/hm-options
 go build ./cmd/lab-monitoring
+go build ./cmd/git-explorer
 ```
 
 ## License

cmd/git-explorer/main.go

@@ -0,0 +1,459 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"log"
+	"os"
+	"os/signal"
+	"syscall"
+	"time"
+
+	"github.com/urfave/cli/v2"
+
+	"git.t-juice.club/torjus/labmcp/internal/gitexplorer"
+	"git.t-juice.club/torjus/labmcp/internal/mcp"
+)
+
+const version = "0.1.0"
+
+func main() {
+	app := &cli.App{
+		Name:    "git-explorer",
+		Usage:   "Read-only MCP server for git repository exploration",
+		Version: version,
+		Flags: []cli.Flag{
+			&cli.StringFlag{
+				Name:    "repo",
+				Aliases: []string{"r"},
+				Usage:   "Path to git repository",
+				EnvVars: []string{"GIT_REPO_PATH"},
+				Value:   ".",
+			},
+			&cli.StringFlag{
+				Name:    "default-remote",
+				Usage:   "Default remote name",
+				EnvVars: []string{"GIT_DEFAULT_REMOTE"},
+				Value:   "origin",
+			},
+		},
+		Commands: []*cli.Command{
+			serveCommand(),
+			resolveCommand(),
+			logCommand(),
+			showCommand(),
+			diffCommand(),
+			catCommand(),
+			branchesCommand(),
+			searchCommand(),
+		},
+	}
+
+	if err := app.Run(os.Args); err != nil {
+		log.Fatal(err)
+	}
+}
+
+func serveCommand() *cli.Command {
+	return &cli.Command{
+		Name:  "serve",
+		Usage: "Run MCP server for git exploration",
+		Flags: []cli.Flag{
+			&cli.StringFlag{
+				Name:    "transport",
+				Aliases: []string{"t"},
+				Usage:   "Transport type: 'stdio' or 'http'",
+				Value:   "stdio",
+			},
+			&cli.StringFlag{
+				Name:  "http-address",
+				Usage: "HTTP listen address",
+				Value: "127.0.0.1:8085",
+			},
+			&cli.StringFlag{
+				Name:  "http-endpoint",
+				Usage: "HTTP endpoint path",
+				Value: "/mcp",
+			},
+			&cli.StringSliceFlag{
+				Name:  "allowed-origins",
+				Usage: "Allowed Origin headers for CORS",
+			},
+			&cli.StringFlag{
+				Name:  "tls-cert",
+				Usage: "TLS certificate file",
+			},
+			&cli.StringFlag{
+				Name:  "tls-key",
+				Usage: "TLS key file",
+			},
+			&cli.DurationFlag{
+				Name:  "session-ttl",
+				Usage: "Session TTL for HTTP transport",
+				Value: 30 * time.Minute,
+			},
+		},
+		Action: func(c *cli.Context) error {
+			return runServe(c)
+		},
+	}
+}
+
+func resolveCommand() *cli.Command {
+	return &cli.Command{
+		Name:      "resolve",
+		Usage:     "Resolve a ref to a commit hash",
+		ArgsUsage: "<ref>",
+		Action: func(c *cli.Context) error {
+			if c.NArg() < 1 {
+				return fmt.Errorf("ref argument required")
+			}
+			return runResolve(c, c.Args().First())
+		},
+	}
+}
+
+func logCommand() *cli.Command {
+	return &cli.Command{
+		Name:  "log",
+		Usage: "Show commit log",
+		Flags: []cli.Flag{
+			&cli.StringFlag{
+				Name:  "ref",
+				Usage: "Starting ref (default: HEAD)",
+				Value: "HEAD",
+			},
+			&cli.IntFlag{
+				Name:    "limit",
+				Aliases: []string{"n"},
+				Usage:   "Maximum number of commits",
+				Value:   10,
+			},
+			&cli.StringFlag{
+				Name:  "author",
+				Usage: "Filter by author",
+			},
+			&cli.StringFlag{
+				Name:  "path",
+				Usage: "Filter by path",
+			},
+		},
+		Action: func(c *cli.Context) error {
+			return runLog(c)
+		},
+	}
+}
+
+func showCommand() *cli.Command {
+	return &cli.Command{
+		Name:      "show",
+		Usage:     "Show commit details",
+		ArgsUsage: "<ref>",
+		Flags: []cli.Flag{
+			&cli.BoolFlag{
+				Name:  "stats",
+				Usage: "Include file statistics",
+				Value: true,
+			},
+		},
+		Action: func(c *cli.Context) error {
+			ref := "HEAD"
+			if c.NArg() > 0 {
+				ref = c.Args().First()
+			}
+			return runShow(c, ref)
+		},
+	}
+}
+
+func diffCommand() *cli.Command {
+	return &cli.Command{
+		Name:      "diff",
+		Usage:     "Show files changed between two commits",
+		ArgsUsage: "<from-ref> <to-ref>",
+		Action: func(c *cli.Context) error {
+			if c.NArg() < 2 {
+				return fmt.Errorf("both from-ref and to-ref arguments required")
+			}
+			return runDiff(c, c.Args().Get(0), c.Args().Get(1))
+		},
+	}
+}
+
+func catCommand() *cli.Command {
+	return &cli.Command{
+		Name:      "cat",
+		Usage:     "Show file contents at a commit",
+		ArgsUsage: "<ref> <path>",
+		Action: func(c *cli.Context) error {
+			if c.NArg() < 2 {
+				return fmt.Errorf("both ref and path arguments required")
+			}
+			return runCat(c, c.Args().Get(0), c.Args().Get(1))
+		},
+	}
+}
+
+func branchesCommand() *cli.Command {
+	return &cli.Command{
+		Name:  "branches",
+		Usage: "List branches",
+		Flags: []cli.Flag{
+			&cli.BoolFlag{
+				Name:    "remote",
+				Aliases: []string{"r"},
+				Usage:   "Include remote branches",
+			},
+		},
+		Action: func(c *cli.Context) error {
+			return runBranches(c)
+		},
+	}
+}
+
+func searchCommand() *cli.Command {
+	return &cli.Command{
+		Name:      "search",
+		Usage:     "Search commit messages",
+		ArgsUsage: "<query>",
+		Flags: []cli.Flag{
+			&cli.StringFlag{
+				Name:  "ref",
+				Usage: "Starting ref (default: HEAD)",
+				Value: "HEAD",
+			},
+			&cli.IntFlag{
+				Name:    "limit",
+				Aliases: []string{"n"},
+				Usage:   "Maximum number of results",
+				Value:   20,
+			},
+		},
+		Action: func(c *cli.Context) error {
+			if c.NArg() < 1 {
+				return fmt.Errorf("query argument required")
+			}
+			return runSearch(c, c.Args().First())
+		},
+	}
+}
+
+func runServe(c *cli.Context) error {
+	ctx, cancel := signal.NotifyContext(context.Background(), syscall.SIGINT, syscall.SIGTERM)
+	defer cancel()
+
+	repoPath := c.String("repo")
+	client, err := gitexplorer.NewGitClient(repoPath, c.String("default-remote"))
+	if err != nil {
+		return fmt.Errorf("failed to open repository: %w", err)
+	}
+
+	logger := log.New(os.Stderr, "[mcp] ", log.LstdFlags)
+	config := mcp.DefaultGitExplorerConfig()
+
+	server := mcp.NewGenericServer(logger, config)
+	gitexplorer.RegisterHandlers(server, client)
+
+	transport := c.String("transport")
+	switch transport {
+	case "stdio":
+		logger.Printf("Starting git-explorer MCP server on stdio (repo: %s)...", repoPath)
+		return server.Run(ctx, os.Stdin, os.Stdout)
+
+	case "http":
+		httpConfig := mcp.HTTPConfig{
+			Address:        c.String("http-address"),
+			Endpoint:       c.String("http-endpoint"),
+			AllowedOrigins: c.StringSlice("allowed-origins"),
+			SessionTTL:     c.Duration("session-ttl"),
+			TLSCertFile:    c.String("tls-cert"),
+			TLSKeyFile:     c.String("tls-key"),
+		}
+		httpTransport := mcp.NewHTTPTransport(server, httpConfig)
+		return httpTransport.Run(ctx)
+
+	default:
+		return fmt.Errorf("unknown transport: %s (use 'stdio' or 'http')", transport)
+	}
+}
+
+func getClient(c *cli.Context) (*gitexplorer.GitClient, error) {
+	return gitexplorer.NewGitClient(c.String("repo"), c.String("default-remote"))
+}
+
+func runResolve(c *cli.Context, ref string) error {
+	client, err := getClient(c)
+	if err != nil {
+		return err
+	}
+
+	result, err := client.ResolveRef(ref)
+	if err != nil {
+		return err
+	}
+
+	fmt.Printf("%s (%s) -> %s\n", result.Ref, result.Type, result.Commit)
+	return nil
+}
+
+func runLog(c *cli.Context) error {
+	client, err := getClient(c)
+	if err != nil {
+		return err
+	}
+
+	entries, err := client.GetLog(
+		c.String("ref"),
+		c.Int("limit"),
+		c.String("author"),
+		"",
+		c.String("path"),
+	)
+	if err != nil {
+		return err
+	}
+
+	if len(entries) == 0 {
+		fmt.Println("No commits found.")
+		return nil
+	}
+
+	for _, e := range entries {
+		fmt.Printf("%s %s\n", e.ShortHash, e.Subject)
+		fmt.Printf("  Author: %s <%s>\n", e.Author, e.Email)
+		fmt.Printf("  Date:   %s\n\n", e.Date.Format("2006-01-02 15:04:05"))
+	}
+
+	return nil
+}
+
+func runShow(c *cli.Context, ref string) error {
+	client, err := getClient(c)
+	if err != nil {
+		return err
+	}
+
+	info, err := client.GetCommitInfo(ref, c.Bool("stats"))
+	if err != nil {
+		return err
+	}
+
+	fmt.Printf("commit %s\n", info.Hash)
+	fmt.Printf("Author: %s <%s>\n", info.Author, info.Email)
+	fmt.Printf("Date:   %s\n", info.Date.Format("2006-01-02 15:04:05"))
+
+	if len(info.Parents) > 0 {
+		fmt.Printf("Parents: %v\n", info.Parents)
+	}
+
+	if info.Stats != nil {
+		fmt.Printf("\n%d file(s) changed, %d insertions(+), %d deletions(-)\n",
+			info.Stats.FilesChanged, info.Stats.Additions, info.Stats.Deletions)
+	}
+
+	fmt.Printf("\n%s", info.Message)
+
+	return nil
+}
+
+func runDiff(c *cli.Context, fromRef, toRef string) error {
+	client, err := getClient(c)
+	if err != nil {
+		return err
+	}
+
+	result, err := client.GetDiffFiles(fromRef, toRef)
+	if err != nil {
+		return err
+	}
+
+	if len(result.Files) == 0 {
+		fmt.Println("No files changed.")
+		return nil
+	}
+
+	fmt.Printf("Comparing %s..%s\n\n", result.FromCommit[:7], result.ToCommit[:7])
+
+	for _, f := range result.Files {
+		status := f.Status[0:1] // First letter: A, M, D, R
+		path := f.Path
+		if f.OldPath != "" {
+			path = fmt.Sprintf("%s -> %s", f.OldPath, f.Path)
+		}
+		fmt.Printf("%s  %s  (+%d -%d)\n", status, path, f.Additions, f.Deletions)
+	}
+
+	return nil
+}
+
+func runCat(c *cli.Context, ref, path string) error {
+	client, err := getClient(c)
+	if err != nil {
+		return err
+	}
+
+	content, err := client.GetFileAtCommit(ref, path)
+	if err != nil {
+		return err
+	}
+
+	fmt.Print(content.Content)
+	return nil
+}
+
+func runBranches(c *cli.Context) error {
+	client, err := getClient(c)
+	if err != nil {
+		return err
+	}
+
+	result, err := client.ListBranches(c.Bool("remote"))
+	if err != nil {
+		return err
+	}
+
+	if result.Total == 0 {
+		fmt.Println("No branches found.")
+		return nil
+	}
+
+	for _, b := range result.Branches {
+		marker := " "
+		if b.IsHead {
+			marker = "*"
+		}
+		remoteMarker := ""
+		if b.IsRemote {
+			remoteMarker = " (remote)"
+		}
+		fmt.Printf("%s %s -> %s%s\n", marker, b.Name, b.Commit[:7], remoteMarker)
+	}
+
+	return nil
+}
+
+func runSearch(c *cli.Context, query string) error {
+	client, err := getClient(c)
+	if err != nil {
+		return err
+	}
+
+	result, err := client.SearchCommits(c.String("ref"), query, c.Int("limit"))
+	if err != nil {
+		return err
+	}
+
+	if result.Count == 0 {
+		fmt.Printf("No commits matching '%s'.\n", query)
+		return nil
+	}
+
+	fmt.Printf("Found %d commit(s) matching '%s':\n\n", result.Count, query)
+	for _, e := range result.Commits {
+		fmt.Printf("%s %s\n", e.ShortHash, e.Subject)
+		fmt.Printf("  Author: %s <%s>\n", e.Author, e.Email)
+		fmt.Printf("  Date:   %s\n\n", e.Date.Format("2006-01-02 15:04:05"))
+	}
+
+	return nil
+}

flake.nix

@@ -40,6 +40,13 @@
             mainProgram = "lab-monitoring";
             description = "MCP server for Prometheus and Alertmanager monitoring";
           };
+          git-explorer = pkgs.callPackage ./nix/package.nix {
+            src = ./.;
+            pname = "git-explorer";
+            subPackage = "cmd/git-explorer";
+            mainProgram = "git-explorer";
+            description = "Read-only MCP server for git repository exploration";
+          };
           default = self.packages.${system}.nixpkgs-search;
         });
 
@@ -84,6 +91,10 @@
           imports = [ ./nix/lab-monitoring-module.nix ];
           services.lab-monitoring.package = lib.mkDefault self.packages.${pkgs.system}.lab-monitoring;
         };
+        git-explorer-mcp = { pkgs, ... }: {
+          imports = [ ./nix/git-explorer-module.nix ];
+          services.git-explorer.package = lib.mkDefault self.packages.${pkgs.system}.git-explorer;
+        };
         default = self.nixosModules.nixpkgs-search-mcp;
       };
     };

go.mod

@@ -9,16 +9,35 @@ require (
 )
 
 require (
+	dario.cat/mergo v1.0.0 // indirect
+	github.com/Microsoft/go-winio v0.6.2 // indirect
+	github.com/ProtonMail/go-crypto v1.1.6 // indirect
+	github.com/cloudflare/circl v1.6.1 // indirect
 	github.com/cpuguy83/go-md2man/v2 v2.0.5 // indirect
+	github.com/cyphar/filepath-securejoin v0.4.1 // indirect
 	github.com/dustin/go-humanize v1.0.1 // indirect
+	github.com/emirpasic/gods v1.18.1 // indirect
+	github.com/go-git/gcfg v1.5.1-0.20230307220236-3a3c6141e376 // indirect
+	github.com/go-git/go-billy/v5 v5.6.2 // indirect
+	github.com/go-git/go-git/v5 v5.16.4 // indirect
+	github.com/golang/groupcache v0.0.0-20241129210726-2c02b8208cf8 // indirect
 	github.com/google/uuid v1.6.0 // indirect
 	github.com/hashicorp/golang-lru/v2 v2.0.7 // indirect
+	github.com/jbenet/go-context v0.0.0-20150711004518-d14ea06fba99 // indirect
+	github.com/kevinburke/ssh_config v1.2.0 // indirect
 	github.com/mattn/go-isatty v0.0.20 // indirect
 	github.com/ncruces/go-strftime v0.1.9 // indirect
+	github.com/pjbgf/sha1cd v0.3.2 // indirect
 	github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec // indirect
 	github.com/russross/blackfriday/v2 v2.1.0 // indirect
+	github.com/sergi/go-diff v1.3.2-0.20230802210424-5b0b94c5c0d3 // indirect
+	github.com/skeema/knownhosts v1.3.1 // indirect
+	github.com/xanzy/ssh-agent v0.3.3 // indirect
 	github.com/xrash/smetrics v0.0.0-20240521201337-686a1a2994c1 // indirect
-	golang.org/x/sys v0.22.0 // indirect
+	golang.org/x/crypto v0.37.0 // indirect
+	golang.org/x/net v0.39.0 // indirect
+	golang.org/x/sys v0.32.0 // indirect
+	gopkg.in/warnings.v0 v0.1.2 // indirect
 	modernc.org/gc/v3 v3.0.0-20240107210532-573471604cb6 // indirect
 	modernc.org/libc v1.55.3 // indirect
 	modernc.org/mathutil v1.6.0 // indirect

go.sum

@@ -1,36 +1,103 @@
+dario.cat/mergo v1.0.0 h1:AGCNq9Evsj31mOgNPcLyXc+4PNABt905YmuqPYYpBWk=
+dario.cat/mergo v1.0.0/go.mod h1:uNxQE+84aUszobStD9th8a29P2fMDhsBdgRYvZOxGmk=
+github.com/Microsoft/go-winio v0.5.2/go.mod h1:WpS1mjBmmwHBEWmogvA2mj8546UReBk4v8QkMxJ6pZY=
+github.com/Microsoft/go-winio v0.6.2 h1:F2VQgta7ecxGYO8k3ZZz3RS8fVIXVxONVUPlNERoyfY=
+github.com/Microsoft/go-winio v0.6.2/go.mod h1:yd8OoFMLzJbo9gZq8j5qaps8bJ9aShtEA8Ipt1oGCvU=
+github.com/ProtonMail/go-crypto v1.1.6 h1:ZcV+Ropw6Qn0AX9brlQLAUXfqLBc7Bl+f/DmNxpLfdw=
+github.com/ProtonMail/go-crypto v1.1.6/go.mod h1:rA3QumHc/FZ8pAHreoekgiAbzpNsfQAosU5td4SnOrE=
+github.com/cloudflare/circl v1.6.1 h1:zqIqSPIndyBh1bjLVVDHMPpVKqp8Su/V+6MeDzzQBQ0=
+github.com/cloudflare/circl v1.6.1/go.mod h1:uddAzsPgqdMAYatqJ0lsjX1oECcQLIlRpzZh3pJrofs=
 github.com/cpuguy83/go-md2man/v2 v2.0.5 h1:ZtcqGrnekaHpVLArFSe4HK5DoKx1T0rq2DwVB0alcyc=
 github.com/cpuguy83/go-md2man/v2 v2.0.5/go.mod h1:tgQtvFlXSQOSOSIRvRPT7W67SCa46tRHOmNcaadrF8o=
+github.com/cyphar/filepath-securejoin v0.4.1 h1:JyxxyPEaktOD+GAnqIqTf9A8tHyAG22rowi7HkoSU1s=
+github.com/cyphar/filepath-securejoin v0.4.1/go.mod h1:Sdj7gXlvMcPZsbhwhQ33GguGLDGQL7h7bg04C/+u9jI=
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/dustin/go-humanize v1.0.1 h1:GzkhY7T5VNhEkwH0PVJgjz+fX1rhBrR7pRT3mDkpeCY=
 github.com/dustin/go-humanize v1.0.1/go.mod h1:Mu1zIs6XwVuF/gI1OepvI0qD18qycQx+mFykh5fBlto=
+github.com/emirpasic/gods v1.18.1 h1:FXtiHYKDGKCW2KzwZKx0iC0PQmdlorYgdFG9jPXJ1Bc=
+github.com/emirpasic/gods v1.18.1/go.mod h1:8tpGGwCnJ5H4r6BWwaV6OrWmMoPhUl5jm/FMNAnJvWQ=
+github.com/go-git/gcfg v1.5.1-0.20230307220236-3a3c6141e376 h1:+zs/tPmkDkHx3U66DAb0lQFJrpS6731Oaa12ikc+DiI=
+github.com/go-git/gcfg v1.5.1-0.20230307220236-3a3c6141e376/go.mod h1:an3vInlBmSxCcxctByoQdvwPiA7DTK7jaaFDBTtu0ic=
+github.com/go-git/go-billy/v5 v5.6.2 h1:6Q86EsPXMa7c3YZ3aLAQsMA0VlWmy43r6FHqa/UNbRM=
+github.com/go-git/go-billy/v5 v5.6.2/go.mod h1:rcFC2rAsp/erv7CMz9GczHcuD0D32fWzH+MJAU+jaUU=
+github.com/go-git/go-git/v5 v5.16.4 h1:7ajIEZHZJULcyJebDLo99bGgS0jRrOxzZG4uCk2Yb2Y=
+github.com/go-git/go-git/v5 v5.16.4/go.mod h1:4Ge4alE/5gPs30F2H1esi2gPd69R0C39lolkucHBOp8=
+github.com/golang/groupcache v0.0.0-20241129210726-2c02b8208cf8 h1:f+oWsMOmNPc8JmEHVZIycC7hBoQxHH9pNKQORJNozsQ=
+github.com/golang/groupcache v0.0.0-20241129210726-2c02b8208cf8/go.mod h1:wcDNUvekVysuuOpQKo3191zZyTpiI6se1N1ULghS0sw=
 github.com/google/pprof v0.0.0-20240409012703-83162a5b38cd h1:gbpYu9NMq8jhDVbvlGkMFWCjLFlqqEZjEmObmhUy6Vo=
 github.com/google/pprof v0.0.0-20240409012703-83162a5b38cd/go.mod h1:kf6iHlnVGwgKolg33glAes7Yg/8iWP8ukqeldJSO7jw=
 github.com/google/uuid v1.6.0 h1:NIvaJDMOsjHA8n1jAhLSgzrAzy1Hgr+hNrb57e+94F0=
 github.com/google/uuid v1.6.0/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
 github.com/hashicorp/golang-lru/v2 v2.0.7 h1:a+bsQ5rvGLjzHuww6tVxozPZFVghXaHOwFs4luLUK2k=
 github.com/hashicorp/golang-lru/v2 v2.0.7/go.mod h1:QeFd9opnmA6QUJc5vARoKUSoFhyfM2/ZepoAG6RGpeM=
+github.com/jbenet/go-context v0.0.0-20150711004518-d14ea06fba99 h1:BQSFePA1RWJOlocH6Fxy8MmwDt+yVQYULKfN0RoTN8A=
+github.com/jbenet/go-context v0.0.0-20150711004518-d14ea06fba99/go.mod h1:1lJo3i6rXxKeerYnT8Nvf0QmHCRC1n8sfWVwXF2Frvo=
+github.com/kevinburke/ssh_config v1.2.0 h1:x584FjTGwHzMwvHx18PXxbBVzfnxogHaAReU4gf13a4=
+github.com/kevinburke/ssh_config v1.2.0/go.mod h1:CT57kijsi8u/K/BOFA39wgDQJ9CxiF4nAY/ojJ6r6mM=
+github.com/kr/pretty v0.1.0/go.mod h1:dAy3ld7l9f0ibDNOQOHHMYYIIbhfbHSm3C4ZsoJORNo=
+github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
+github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
 github.com/lib/pq v1.10.9 h1:YXG7RB+JIjhP29X+OtkiDnYaXQwpS4JEWq7dtCCRUEw=
 github.com/lib/pq v1.10.9/go.mod h1:AlVN5x4E4T544tWzH6hKfbfQvm3HdbOxrmggDNAPY9o=
 github.com/mattn/go-isatty v0.0.20 h1:xfD0iDuEKnDkl03q4limB+vH+GxLEtL/jb4xVJSWWEY=
 github.com/mattn/go-isatty v0.0.20/go.mod h1:W+V8PltTTMOvKvAeJH7IuucS94S2C6jfK/D7dTCTo3Y=
 github.com/ncruces/go-strftime v0.1.9 h1:bY0MQC28UADQmHmaF5dgpLmImcShSi2kHU9XLdhx/f4=
 github.com/ncruces/go-strftime v0.1.9/go.mod h1:Fwc5htZGVVkseilnfgOVb9mKy6w1naJmn9CehxcKcls=
+github.com/pjbgf/sha1cd v0.3.2 h1:a9wb0bp1oC2TGwStyn0Umc/IGKQnEgF0vVaZ8QF8eo4=
+github.com/pjbgf/sha1cd v0.3.2/go.mod h1:zQWigSxVmsHEZow5qaLtPYxpcKMMQpa09ixqBxuCS6A=
+github.com/pkg/errors v0.9.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec h1:W09IVJc94icq4NjY3clb7Lk8O1qJ8BdBEF8z0ibU0rE=
 github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec/go.mod h1:qqbHyh8v60DhA7CoWK5oRCqLrMHRGoxYCSS9EjAz6Eo=
 github.com/russross/blackfriday/v2 v2.1.0 h1:JIOH55/0cWyOuilr9/qlrm0BSXldqnqwMsf35Ld67mk=
 github.com/russross/blackfriday/v2 v2.1.0/go.mod h1:+Rmxgy9KzJVeS9/2gXHxylqXiyQDYRxCVz55jmeOWTM=
+github.com/sergi/go-diff v1.3.2-0.20230802210424-5b0b94c5c0d3 h1:n661drycOFuPLCN3Uc8sB6B/s6Z4t2xvBgU1htSHuq8=
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+github.com/sirupsen/logrus v1.7.0/go.mod h1:yWOB1SBYBC5VeMP7gHvWumXLIWorT60ONWic61uBYv0=
+github.com/skeema/knownhosts v1.3.1 h1:X2osQ+RAjK76shCbvhHHHVl3ZlgDm8apHEHFqRjnBY8=
+github.com/skeema/knownhosts v1.3.1/go.mod h1:r7KTdC8l4uxWRyK2TpQZ/1o5HaSzh06ePQNxPwTcfiY=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
+github.com/stretchr/testify v1.4.0/go.mod h1:j7eGeouHqKxXV5pUuKE4zz7dFj8WfuZ+81PSLYec5m4=
 github.com/urfave/cli/v2 v2.27.5 h1:WoHEJLdsXr6dDWoJgMq/CboDmyY/8HMMH1fTECbih+w=
 github.com/urfave/cli/v2 v2.27.5/go.mod h1:3Sevf16NykTbInEnD0yKkjDAeZDS0A6bzhBH5hrMvTQ=
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 github.com/xrash/smetrics v0.0.0-20240521201337-686a1a2994c1 h1:gEOO8jv9F4OT7lGCjxCBTO/36wtF6j2nSip77qHd4x4=
 github.com/xrash/smetrics v0.0.0-20240521201337-686a1a2994c1/go.mod h1:Ohn+xnUBiLI6FVj/9LpzZWtj1/D6lUovWYBkxHVV3aM=
+golang.org/x/crypto v0.0.0-20220622213112-05595931fe9d/go.mod h1:IxCIyHEi3zRg3s0A5j5BB6A9Jmi73HwBIUl50j+osU4=
+golang.org/x/crypto v0.37.0 h1:kJNSjF/Xp7kU0iB2Z+9viTPMW4EqqsrywMXLJOOsXSE=
+golang.org/x/crypto v0.37.0/go.mod h1:vg+k43peMZ0pUMhYmVAWysMK35e6ioLh3wB8ZCAfbVc=
 golang.org/x/mod v0.16.0 h1:QX4fJ0Rr5cPQCF7O9lh9Se4pmwfwskqZfq5moyldzic=
 golang.org/x/mod v0.16.0/go.mod h1:hTbmBsO62+eylJbnUtE2MGJUyE7QWk4xUqPFrRgJ+7c=
+golang.org/x/net v0.0.0-20211112202133-69e39bad7dc2/go.mod h1:9nx3DQGgdP8bBQD5qxJ1jj9UTztislL4KSBs9R2vV5Y=
+golang.org/x/net v0.39.0 h1:ZCu7HMWDxpXpaiKdhzIfaltL9Lp31x/3fCP11bc6/fY=
+golang.org/x/net v0.39.0/go.mod h1:X7NRbYVEA+ewNkCNyJ513WmMdQ3BineSwVtN2zD/d+E=
+golang.org/x/sys v0.0.0-20191026070338-33540a1f6037/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20201119102817-f84b799fce68/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20210124154548-22da62e12c0c/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20210423082822-04245dca01da/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20210615035016-665e8c7367d1/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.0.0-20220715151400-c0bba94af5f8/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.6.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.22.0 h1:RI27ohtqKCnwULzJLqkv897zojh5/DwS/ENaMzUOaWI=
 golang.org/x/sys v0.22.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
+golang.org/x/sys v0.32.0 h1:s77OFDvIQeibCmezSnk/q6iAfkdiQaJi4VzroCFrN20=
+golang.org/x/sys v0.32.0/go.mod h1:BJP2sWEmIv4KK5OTEluFJCKSidICx8ciO85XgH3Ak8k=
+golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
+golang.org/x/text v0.3.6/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
+golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
 golang.org/x/tools v0.19.0 h1:tfGCXNR1OsFG+sVdLAitlpjAvD/I6dHDKnYrpEZUHkw=
 golang.org/x/tools v0.19.0/go.mod h1:qoJWxmGSIBmAeriMx19ogtrEPrGtDbPK634QFIcLAhc=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/check.v1 v1.0.0-20190902080502-41f04d3bba15/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/warnings.v0 v0.1.2 h1:wFXVbFY8DY5/xOe1ECiWdKCzZlxgshcYVNkBHstARME=
+gopkg.in/warnings.v0 v0.1.2/go.mod h1:jksf8JmL6Qr/oQM2OXTHunEvvTAsrWBLb6OOjuVWRNI=
+gopkg.in/yaml.v2 v2.2.2/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
+gopkg.in/yaml.v2 v2.4.0/go.mod h1:RDklbk79AGWmwhnvt/jBztapEOGDOx6ZbXqjP6csGnQ=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
 modernc.org/cc/v4 v4.21.4 h1:3Be/Rdo1fpr8GrQ7IVw9OHtplU4gWbb+wNgeoBMmGLQ=
 modernc.org/cc/v4 v4.21.4/go.mod h1:HM7VJTZbUCR3rV8EYBi9wxnJ0ZBRiGE5OeGXNA0IsLQ=
 modernc.org/ccgo/v4 v4.19.2 h1:lwQZgvboKD0jBwdaeVCTouxhxAyN6iawF3STraAal8Y=

internal/gitexplorer/client.go

@@ -0,0 +1,570 @@
+package gitexplorer
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"strings"
+
+	"github.com/go-git/go-git/v5"
+	"github.com/go-git/go-git/v5/plumbing"
+	"github.com/go-git/go-git/v5/plumbing/object"
+)
+
+var (
+	// ErrNotFound is returned when a ref, commit, or file is not found.
+	ErrNotFound = errors.New("not found")
+	// ErrFileTooLarge is returned when a file exceeds the size limit.
+	ErrFileTooLarge = errors.New("file too large")
+)
+
+// GitClient provides read-only access to a git repository.
+type GitClient struct {
+	repo          *git.Repository
+	defaultRemote string
+}
+
+// NewGitClient opens a git repository at the given path.
+func NewGitClient(repoPath string, defaultRemote string) (*GitClient, error) {
+	repo, err := git.PlainOpen(repoPath)
+	if err != nil {
+		return nil, fmt.Errorf("failed to open repository: %w", err)
+	}
+
+	if defaultRemote == "" {
+		defaultRemote = "origin"
+	}
+
+	return &GitClient{
+		repo:          repo,
+		defaultRemote: defaultRemote,
+	}, nil
+}
+
+// ResolveRef resolves a ref (branch, tag, or commit hash) to a commit hash.
+func (c *GitClient) ResolveRef(ref string) (*ResolveResult, error) {
+	result := &ResolveResult{Ref: ref}
+
+	// Try to resolve as a revision
+	hash, err := c.repo.ResolveRevision(plumbing.Revision(ref))
+	if err != nil {
+		return nil, fmt.Errorf("%w: ref '%s'", ErrNotFound, ref)
+	}
+
+	result.Commit = hash.String()
+
+	// Determine the type of ref
+	// Check if it's a branch
+	if _, err := c.repo.Reference(plumbing.NewBranchReferenceName(ref), true); err == nil {
+		result.Type = "branch"
+		return result, nil
+	}
+
+	// Check if it's a remote branch
+	if _, err := c.repo.Reference(plumbing.NewRemoteReferenceName(c.defaultRemote, ref), true); err == nil {
+		result.Type = "branch"
+		return result, nil
+	}
+
+	// Check if it's a tag
+	if _, err := c.repo.Reference(plumbing.NewTagReferenceName(ref), true); err == nil {
+		result.Type = "tag"
+		return result, nil
+	}
+
+	// Default to commit
+	result.Type = "commit"
+	return result, nil
+}
+
+// GetLog returns the commit log starting from the given ref.
+func (c *GitClient) GetLog(ref string, limit int, author string, since string, path string) ([]LogEntry, error) {
+	if limit <= 0 || limit > Limits.MaxLogEntries {
+		limit = Limits.MaxLogEntries
+	}
+
+	// Resolve the ref to a commit hash
+	hash, err := c.repo.ResolveRevision(plumbing.Revision(ref))
+	if err != nil {
+		return nil, fmt.Errorf("%w: ref '%s'", ErrNotFound, ref)
+	}
+
+	logOpts := &git.LogOptions{
+		From: *hash,
+	}
+
+	// Add path filter if specified
+	if path != "" {
+		if err := ValidatePath(path); err != nil {
+			return nil, err
+		}
+		logOpts.PathFilter = func(p string) bool {
+			return strings.HasPrefix(p, path) || p == path
+		}
+	}
+
+	iter, err := c.repo.Log(logOpts)
+	if err != nil {
+		return nil, fmt.Errorf("failed to get log: %w", err)
+	}
+	defer iter.Close()
+
+	var entries []LogEntry
+	err = iter.ForEach(func(commit *object.Commit) error {
+		// Apply author filter
+		if author != "" {
+			authorLower := strings.ToLower(author)
+			if !strings.Contains(strings.ToLower(commit.Author.Name), authorLower) &&
+				!strings.Contains(strings.ToLower(commit.Author.Email), authorLower) {
+				return nil
+			}
+		}
+
+		// Apply since filter
+		if since != "" {
+			// Parse since as a ref and check if this commit is reachable
+			sinceHash, err := c.repo.ResolveRevision(plumbing.Revision(since))
+			if err == nil {
+				// Stop if we've reached the since commit
+				if commit.Hash == *sinceHash {
+					return io.EOF
+				}
+			}
+		}
+
+		// Get first line of commit message as subject
+		subject := commit.Message
+		if idx := strings.Index(subject, "\n"); idx != -1 {
+			subject = subject[:idx]
+		}
+		subject = strings.TrimSpace(subject)
+
+		entries = append(entries, LogEntry{
+			Hash:      commit.Hash.String(),
+			ShortHash: commit.Hash.String()[:7],
+			Author:    commit.Author.Name,
+			Email:     commit.Author.Email,
+			Date:      commit.Author.When,
+			Subject:   subject,
+		})
+
+		if len(entries) >= limit {
+			return io.EOF
+		}
+		return nil
+	})
+
+	// io.EOF is expected when we hit the limit
+	if err != nil && err != io.EOF {
+		return nil, fmt.Errorf("failed to iterate log: %w", err)
+	}
+
+	return entries, nil
+}
+
+// GetCommitInfo returns full details about a commit.
+func (c *GitClient) GetCommitInfo(ref string, includeStats bool) (*CommitInfo, error) {
+	hash, err := c.repo.ResolveRevision(plumbing.Revision(ref))
+	if err != nil {
+		return nil, fmt.Errorf("%w: ref '%s'", ErrNotFound, ref)
+	}
+
+	commit, err := c.repo.CommitObject(*hash)
+	if err != nil {
+		return nil, fmt.Errorf("failed to get commit: %w", err)
+	}
+
+	info := &CommitInfo{
+		Hash:       commit.Hash.String(),
+		Author:     commit.Author.Name,
+		Email:      commit.Author.Email,
+		Date:       commit.Author.When,
+		Committer:  commit.Committer.Name,
+		CommitDate: commit.Committer.When,
+		Message:    commit.Message,
+	}
+
+	for _, parent := range commit.ParentHashes {
+		info.Parents = append(info.Parents, parent.String())
+	}
+
+	if includeStats {
+		stats, err := c.getCommitStats(commit)
+		if err == nil {
+			info.Stats = stats
+		}
+	}
+
+	return info, nil
+}
+
+// getCommitStats computes file change statistics for a commit.
+func (c *GitClient) getCommitStats(commit *object.Commit) (*FileStats, error) {
+	stats, err := commit.Stats()
+	if err != nil {
+		return nil, err
+	}
+
+	result := &FileStats{
+		FilesChanged: len(stats),
+	}
+
+	for _, s := range stats {
+		result.Additions += s.Addition
+		result.Deletions += s.Deletion
+	}
+
+	return result, nil
+}
+
+// GetDiffFiles returns the files changed between two commits.
+func (c *GitClient) GetDiffFiles(fromRef, toRef string) (*DiffResult, error) {
+	fromHash, err := c.repo.ResolveRevision(plumbing.Revision(fromRef))
+	if err != nil {
+		return nil, fmt.Errorf("%w: ref '%s'", ErrNotFound, fromRef)
+	}
+
+	toHash, err := c.repo.ResolveRevision(plumbing.Revision(toRef))
+	if err != nil {
+		return nil, fmt.Errorf("%w: ref '%s'", ErrNotFound, toRef)
+	}
+
+	fromCommit, err := c.repo.CommitObject(*fromHash)
+	if err != nil {
+		return nil, fmt.Errorf("failed to get from commit: %w", err)
+	}
+
+	toCommit, err := c.repo.CommitObject(*toHash)
+	if err != nil {
+		return nil, fmt.Errorf("failed to get to commit: %w", err)
+	}
+
+	patch, err := fromCommit.Patch(toCommit)
+	if err != nil {
+		return nil, fmt.Errorf("failed to get patch: %w", err)
+	}
+
+	result := &DiffResult{
+		FromCommit: fromHash.String(),
+		ToCommit:   toHash.String(),
+	}
+
+	for i, filePatch := range patch.FilePatches() {
+		if i >= Limits.MaxDiffFiles {
+			break
+		}
+
+		from, to := filePatch.Files()
+
+		df := DiffFile{}
+
+		// Determine status and paths
+		switch {
+		case from == nil && to != nil:
+			df.Status = "added"
+			df.Path = to.Path()
+		case from != nil && to == nil:
+			df.Status = "deleted"
+			df.Path = from.Path()
+		case from != nil && to != nil && from.Path() != to.Path():
+			df.Status = "renamed"
+			df.Path = to.Path()
+			df.OldPath = from.Path()
+		default:
+			df.Status = "modified"
+			if to != nil {
+				df.Path = to.Path()
+			} else if from != nil {
+				df.Path = from.Path()
+			}
+		}
+
+		// Count additions and deletions
+		for _, chunk := range filePatch.Chunks() {
+			content := chunk.Content()
+			lines := strings.Split(content, "\n")
+			switch chunk.Type() {
+			case 1: // Add
+				df.Additions += len(lines)
+			case 2: // Delete
+				df.Deletions += len(lines)
+			}
+		}
+
+		result.Files = append(result.Files, df)
+	}
+
+	return result, nil
+}
+
+// GetFileAtCommit returns the content of a file at a specific commit.
+func (c *GitClient) GetFileAtCommit(ref, path string) (*FileContent, error) {
+	if err := ValidatePath(path); err != nil {
+		return nil, err
+	}
+
+	hash, err := c.repo.ResolveRevision(plumbing.Revision(ref))
+	if err != nil {
+		return nil, fmt.Errorf("%w: ref '%s'", ErrNotFound, ref)
+	}
+
+	commit, err := c.repo.CommitObject(*hash)
+	if err != nil {
+		return nil, fmt.Errorf("failed to get commit: %w", err)
+	}
+
+	file, err := commit.File(path)
+	if err != nil {
+		return nil, fmt.Errorf("%w: file '%s'", ErrNotFound, path)
+	}
+
+	// Check file size
+	if file.Size > Limits.MaxFileContent {
+		return nil, fmt.Errorf("%w: %d bytes (max %d)", ErrFileTooLarge, file.Size, Limits.MaxFileContent)
+	}
+
+	content, err := file.Contents()
+	if err != nil {
+		return nil, fmt.Errorf("failed to read file: %w", err)
+	}
+
+	return &FileContent{
+		Path:    path,
+		Commit:  hash.String(),
+		Size:    file.Size,
+		Content: content,
+	}, nil
+}
+
+// IsAncestor checks if ancestor is an ancestor of descendant.
+func (c *GitClient) IsAncestor(ancestorRef, descendantRef string) (*AncestryResult, error) {
+	ancestorHash, err := c.repo.ResolveRevision(plumbing.Revision(ancestorRef))
+	if err != nil {
+		return nil, fmt.Errorf("%w: ref '%s'", ErrNotFound, ancestorRef)
+	}
+
+	descendantHash, err := c.repo.ResolveRevision(plumbing.Revision(descendantRef))
+	if err != nil {
+		return nil, fmt.Errorf("%w: ref '%s'", ErrNotFound, descendantRef)
+	}
+
+	ancestorCommit, err := c.repo.CommitObject(*ancestorHash)
+	if err != nil {
+		return nil, fmt.Errorf("failed to get ancestor commit: %w", err)
+	}
+
+	descendantCommit, err := c.repo.CommitObject(*descendantHash)
+	if err != nil {
+		return nil, fmt.Errorf("failed to get descendant commit: %w", err)
+	}
+
+	isAncestor, err := ancestorCommit.IsAncestor(descendantCommit)
+	if err != nil {
+		return nil, fmt.Errorf("failed to check ancestry: %w", err)
+	}
+
+	return &AncestryResult{
+		Ancestor:   ancestorHash.String(),
+		Descendant: descendantHash.String(),
+		IsAncestor: isAncestor,
+	}, nil
+}
+
+// CommitsBetween returns commits between two refs (exclusive of from, inclusive of to).
+func (c *GitClient) CommitsBetween(fromRef, toRef string, limit int) (*CommitRange, error) {
+	if limit <= 0 || limit > Limits.MaxLogEntries {
+		limit = Limits.MaxLogEntries
+	}
+
+	fromHash, err := c.repo.ResolveRevision(plumbing.Revision(fromRef))
+	if err != nil {
+		return nil, fmt.Errorf("%w: ref '%s'", ErrNotFound, fromRef)
+	}
+
+	toHash, err := c.repo.ResolveRevision(plumbing.Revision(toRef))
+	if err != nil {
+		return nil, fmt.Errorf("%w: ref '%s'", ErrNotFound, toRef)
+	}
+
+	iter, err := c.repo.Log(&git.LogOptions{
+		From: *toHash,
+	})
+	if err != nil {
+		return nil, fmt.Errorf("failed to get log: %w", err)
+	}
+	defer iter.Close()
+
+	result := &CommitRange{
+		FromCommit: fromHash.String(),
+		ToCommit:   toHash.String(),
+	}
+
+	err = iter.ForEach(func(commit *object.Commit) error {
+		// Stop when we reach the from commit (exclusive)
+		if commit.Hash == *fromHash {
+			return io.EOF
+		}
+
+		subject := commit.Message
+		if idx := strings.Index(subject, "\n"); idx != -1 {
+			subject = subject[:idx]
+		}
+		subject = strings.TrimSpace(subject)
+
+		result.Commits = append(result.Commits, LogEntry{
+			Hash:      commit.Hash.String(),
+			ShortHash: commit.Hash.String()[:7],
+			Author:    commit.Author.Name,
+			Email:     commit.Author.Email,
+			Date:      commit.Author.When,
+			Subject:   subject,
+		})
+
+		if len(result.Commits) >= limit {
+			return io.EOF
+		}
+		return nil
+	})
+
+	if err != nil && err != io.EOF {
+		return nil, fmt.Errorf("failed to iterate log: %w", err)
+	}
+
+	result.Count = len(result.Commits)
+	return result, nil
+}
+
+// ListBranches returns all branches in the repository.
+func (c *GitClient) ListBranches(includeRemote bool) (*BranchList, error) {
+	result := &BranchList{}
+
+	// Get HEAD to determine current branch
+	head, err := c.repo.Head()
+	if err == nil && head.Name().IsBranch() {
+		result.Current = head.Name().Short()
+	}
+
+	// List local branches
+	branchIter, err := c.repo.Branches()
+	if err != nil {
+		return nil, fmt.Errorf("failed to list branches: %w", err)
+	}
+
+	err = branchIter.ForEach(func(ref *plumbing.Reference) error {
+		if len(result.Branches) >= Limits.MaxBranches {
+			return io.EOF
+		}
+
+		branch := Branch{
+			Name:     ref.Name().Short(),
+			Commit:   ref.Hash().String(),
+			IsRemote: false,
+			IsHead:   ref.Name().Short() == result.Current,
+		}
+
+		result.Branches = append(result.Branches, branch)
+		return nil
+	})
+	if err != nil && err != io.EOF {
+		return nil, fmt.Errorf("failed to iterate branches: %w", err)
+	}
+
+	// List remote branches if requested
+	if includeRemote {
+		refs, err := c.repo.References()
+		if err != nil {
+			return nil, fmt.Errorf("failed to list references: %w", err)
+		}
+
+		err = refs.ForEach(func(ref *plumbing.Reference) error {
+			if len(result.Branches) >= Limits.MaxBranches {
+				return io.EOF
+			}
+
+			if ref.Name().IsRemote() {
+				branch := Branch{
+					Name:     ref.Name().Short(),
+					Commit:   ref.Hash().String(),
+					IsRemote: true,
+					IsHead:   false,
+				}
+				result.Branches = append(result.Branches, branch)
+			}
+			return nil
+		})
+		if err != nil && err != io.EOF {
+			return nil, fmt.Errorf("failed to iterate references: %w", err)
+		}
+	}
+
+	result.Total = len(result.Branches)
+	return result, nil
+}
+
+// SearchCommits searches commit messages for a pattern.
+func (c *GitClient) SearchCommits(ref, query string, limit int) (*SearchResult, error) {
+	if limit <= 0 || limit > Limits.MaxSearchResult {
+		limit = Limits.MaxSearchResult
+	}
+
+	hash, err := c.repo.ResolveRevision(plumbing.Revision(ref))
+	if err != nil {
+		return nil, fmt.Errorf("%w: ref '%s'", ErrNotFound, ref)
+	}
+
+	iter, err := c.repo.Log(&git.LogOptions{
+		From: *hash,
+	})
+	if err != nil {
+		return nil, fmt.Errorf("failed to get log: %w", err)
+	}
+	defer iter.Close()
+
+	result := &SearchResult{
+		Query: query,
+	}
+	queryLower := strings.ToLower(query)
+
+	// We need to scan more commits to find matches
+	scanned := 0
+	maxScan := limit * 100 // Scan up to 100x the limit
+
+	err = iter.ForEach(func(commit *object.Commit) error {
+		scanned++
+		if scanned > maxScan {
+			return io.EOF
+		}
+
+		// Search in message (case-insensitive)
+		if !strings.Contains(strings.ToLower(commit.Message), queryLower) {
+			return nil
+		}
+
+		subject := commit.Message
+		if idx := strings.Index(subject, "\n"); idx != -1 {
+			subject = subject[:idx]
+		}
+		subject = strings.TrimSpace(subject)
+
+		result.Commits = append(result.Commits, LogEntry{
+			Hash:      commit.Hash.String(),
+			ShortHash: commit.Hash.String()[:7],
+			Author:    commit.Author.Name,
+			Email:     commit.Author.Email,
+			Date:      commit.Author.When,
+			Subject:   subject,
+		})
+
+		if len(result.Commits) >= limit {
+			return io.EOF
+		}
+		return nil
+	})
+
+	if err != nil && err != io.EOF {
+		return nil, fmt.Errorf("failed to search commits: %w", err)
+	}
+
+	result.Count = len(result.Commits)
+	return result, nil
+}

internal/gitexplorer/client_test.go

@@ -0,0 +1,446 @@
+package gitexplorer
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+
+	"github.com/go-git/go-git/v5"
+	"github.com/go-git/go-git/v5/plumbing/object"
+)
+
+// createTestRepo creates a temporary git repository with some commits for testing.
+func createTestRepo(t *testing.T) (string, func()) {
+	t.Helper()
+
+	dir, err := os.MkdirTemp("", "gitexplorer-test-*")
+	if err != nil {
+		t.Fatalf("failed to create temp dir: %v", err)
+	}
+
+	cleanup := func() {
+		_ = os.RemoveAll(dir)
+	}
+
+	repo, err := git.PlainInit(dir, false)
+	if err != nil {
+		cleanup()
+		t.Fatalf("failed to init repo: %v", err)
+	}
+
+	wt, err := repo.Worktree()
+	if err != nil {
+		cleanup()
+		t.Fatalf("failed to get worktree: %v", err)
+	}
+
+	// Create initial file and commit
+	readme := filepath.Join(dir, "README.md")
+	if err := os.WriteFile(readme, []byte("# Test Repo\n"), 0644); err != nil {
+		cleanup()
+		t.Fatalf("failed to write README: %v", err)
+	}
+
+	if _, err := wt.Add("README.md"); err != nil {
+		cleanup()
+		t.Fatalf("failed to add README: %v", err)
+	}
+
+	sig := &object.Signature{
+		Name:  "Test User",
+		Email: "test@example.com",
+		When:  time.Now().Add(-2 * time.Hour),
+	}
+
+	_, err = wt.Commit("Initial commit", &git.CommitOptions{Author: sig})
+	if err != nil {
+		cleanup()
+		t.Fatalf("failed to create initial commit: %v", err)
+	}
+
+	// Create a second file and commit
+	subdir := filepath.Join(dir, "src")
+	if err := os.MkdirAll(subdir, 0755); err != nil {
+		cleanup()
+		t.Fatalf("failed to create subdir: %v", err)
+	}
+
+	mainFile := filepath.Join(subdir, "main.go")
+	if err := os.WriteFile(mainFile, []byte("package main\n\nfunc main() {}\n"), 0644); err != nil {
+		cleanup()
+		t.Fatalf("failed to write main.go: %v", err)
+	}
+
+	if _, err := wt.Add("src/main.go"); err != nil {
+		cleanup()
+		t.Fatalf("failed to add main.go: %v", err)
+	}
+
+	sig.When = time.Now().Add(-1 * time.Hour)
+	_, err = wt.Commit("Add main.go", &git.CommitOptions{Author: sig})
+	if err != nil {
+		cleanup()
+		t.Fatalf("failed to create second commit: %v", err)
+	}
+
+	// Update README and commit
+	if err := os.WriteFile(readme, []byte("# Test Repo\n\nThis is a test repository.\n"), 0644); err != nil {
+		cleanup()
+		t.Fatalf("failed to update README: %v", err)
+	}
+
+	if _, err := wt.Add("README.md"); err != nil {
+		cleanup()
+		t.Fatalf("failed to add updated README: %v", err)
+	}
+
+	sig.When = time.Now()
+	_, err = wt.Commit("Update README", &git.CommitOptions{Author: sig})
+	if err != nil {
+		cleanup()
+		t.Fatalf("failed to create third commit: %v", err)
+	}
+
+	return dir, cleanup
+}
+
+func TestNewGitClient(t *testing.T) {
+	repoPath, cleanup := createTestRepo(t)
+	defer cleanup()
+
+	client, err := NewGitClient(repoPath, "")
+	if err != nil {
+		t.Fatalf("NewGitClient failed: %v", err)
+	}
+	if client == nil {
+		t.Fatal("client is nil")
+	}
+	if client.defaultRemote != "origin" {
+		t.Errorf("defaultRemote = %q, want %q", client.defaultRemote, "origin")
+	}
+
+	// Test with invalid path
+	_, err = NewGitClient("/nonexistent/path", "")
+	if err == nil {
+		t.Error("expected error for nonexistent path")
+	}
+}
+
+func TestResolveRef(t *testing.T) {
+	repoPath, cleanup := createTestRepo(t)
+	defer cleanup()
+
+	client, err := NewGitClient(repoPath, "")
+	if err != nil {
+		t.Fatalf("NewGitClient failed: %v", err)
+	}
+
+	// Test resolving HEAD
+	result, err := client.ResolveRef("HEAD")
+	if err != nil {
+		t.Fatalf("ResolveRef(HEAD) failed: %v", err)
+	}
+	if result.Commit == "" {
+		t.Error("commit hash is empty")
+	}
+
+	// Test resolving master branch
+	result, err = client.ResolveRef("master")
+	if err != nil {
+		t.Fatalf("ResolveRef(master) failed: %v", err)
+	}
+	if result.Type != "branch" {
+		t.Errorf("type = %q, want %q", result.Type, "branch")
+	}
+
+	// Test resolving invalid ref
+	_, err = client.ResolveRef("nonexistent")
+	if err == nil {
+		t.Error("expected error for nonexistent ref")
+	}
+}
+
+func TestGetLog(t *testing.T) {
+	repoPath, cleanup := createTestRepo(t)
+	defer cleanup()
+
+	client, err := NewGitClient(repoPath, "")
+	if err != nil {
+		t.Fatalf("NewGitClient failed: %v", err)
+	}
+
+	// Get full log
+	entries, err := client.GetLog("HEAD", 10, "", "", "")
+	if err != nil {
+		t.Fatalf("GetLog failed: %v", err)
+	}
+	if len(entries) != 3 {
+		t.Errorf("got %d entries, want 3", len(entries))
+	}
+
+	// Check order (newest first)
+	if entries[0].Subject != "Update README" {
+		t.Errorf("first entry subject = %q, want %q", entries[0].Subject, "Update README")
+	}
+
+	// Test with limit
+	entries, err = client.GetLog("HEAD", 1, "", "", "")
+	if err != nil {
+		t.Fatalf("GetLog with limit failed: %v", err)
+	}
+	if len(entries) != 1 {
+		t.Errorf("got %d entries, want 1", len(entries))
+	}
+
+	// Test with author filter
+	entries, err = client.GetLog("HEAD", 10, "Test User", "", "")
+	if err != nil {
+		t.Fatalf("GetLog with author failed: %v", err)
+	}
+	if len(entries) != 3 {
+		t.Errorf("got %d entries, want 3", len(entries))
+	}
+
+	entries, err = client.GetLog("HEAD", 10, "nonexistent", "", "")
+	if err != nil {
+		t.Fatalf("GetLog with nonexistent author failed: %v", err)
+	}
+	if len(entries) != 0 {
+		t.Errorf("got %d entries, want 0", len(entries))
+	}
+
+	// Test with path filter
+	entries, err = client.GetLog("HEAD", 10, "", "", "src")
+	if err != nil {
+		t.Fatalf("GetLog with path failed: %v", err)
+	}
+	if len(entries) != 1 {
+		t.Errorf("got %d entries, want 1 (only src/main.go commit)", len(entries))
+	}
+}
+
+func TestGetCommitInfo(t *testing.T) {
+	repoPath, cleanup := createTestRepo(t)
+	defer cleanup()
+
+	client, err := NewGitClient(repoPath, "")
+	if err != nil {
+		t.Fatalf("NewGitClient failed: %v", err)
+	}
+
+	info, err := client.GetCommitInfo("HEAD", true)
+	if err != nil {
+		t.Fatalf("GetCommitInfo failed: %v", err)
+	}
+
+	if info.Author != "Test User" {
+		t.Errorf("author = %q, want %q", info.Author, "Test User")
+	}
+	if info.Email != "test@example.com" {
+		t.Errorf("email = %q, want %q", info.Email, "test@example.com")
+	}
+	if len(info.Parents) != 1 {
+		t.Errorf("parents = %d, want 1", len(info.Parents))
+	}
+	if info.Stats == nil {
+		t.Error("stats is nil")
+	}
+
+	// Test without stats
+	info, err = client.GetCommitInfo("HEAD", false)
+	if err != nil {
+		t.Fatalf("GetCommitInfo without stats failed: %v", err)
+	}
+	if info.Stats != nil {
+		t.Error("stats should be nil")
+	}
+}
+
+func TestGetDiffFiles(t *testing.T) {
+	repoPath, cleanup := createTestRepo(t)
+	defer cleanup()
+
+	client, err := NewGitClient(repoPath, "")
+	if err != nil {
+		t.Fatalf("NewGitClient failed: %v", err)
+	}
+
+	result, err := client.GetDiffFiles("HEAD~2", "HEAD")
+	if err != nil {
+		t.Fatalf("GetDiffFiles failed: %v", err)
+	}
+
+	if len(result.Files) < 1 {
+		t.Error("expected at least one changed file")
+	}
+
+	// Check that we have the expected files
+	foundReadme := false
+	foundMain := false
+	for _, f := range result.Files {
+		if f.Path == "README.md" {
+			foundReadme = true
+		}
+		if f.Path == "src/main.go" {
+			foundMain = true
+		}
+	}
+	if !foundReadme {
+		t.Error("expected README.md in diff")
+	}
+	if !foundMain {
+		t.Error("expected src/main.go in diff")
+	}
+}
+
+func TestGetFileAtCommit(t *testing.T) {
+	repoPath, cleanup := createTestRepo(t)
+	defer cleanup()
+
+	client, err := NewGitClient(repoPath, "")
+	if err != nil {
+		t.Fatalf("NewGitClient failed: %v", err)
+	}
+
+	content, err := client.GetFileAtCommit("HEAD", "README.md")
+	if err != nil {
+		t.Fatalf("GetFileAtCommit failed: %v", err)
+	}
+
+	if content.Path != "README.md" {
+		t.Errorf("path = %q, want %q", content.Path, "README.md")
+	}
+	if content.Content == "" {
+		t.Error("content is empty")
+	}
+
+	// Test nested file
+	content, err = client.GetFileAtCommit("HEAD", "src/main.go")
+	if err != nil {
+		t.Fatalf("GetFileAtCommit for nested file failed: %v", err)
+	}
+	if content.Path != "src/main.go" {
+		t.Errorf("path = %q, want %q", content.Path, "src/main.go")
+	}
+
+	// Test nonexistent file
+	_, err = client.GetFileAtCommit("HEAD", "nonexistent.txt")
+	if err == nil {
+		t.Error("expected error for nonexistent file")
+	}
+
+	// Test path traversal
+	_, err = client.GetFileAtCommit("HEAD", "../../../etc/passwd")
+	if err == nil {
+		t.Error("expected error for path traversal")
+	}
+}
+
+func TestIsAncestor(t *testing.T) {
+	repoPath, cleanup := createTestRepo(t)
+	defer cleanup()
+
+	client, err := NewGitClient(repoPath, "")
+	if err != nil {
+		t.Fatalf("NewGitClient failed: %v", err)
+	}
+
+	// First commit is ancestor of HEAD
+	result, err := client.IsAncestor("HEAD~2", "HEAD")
+	if err != nil {
+		t.Fatalf("IsAncestor failed: %v", err)
+	}
+	if !result.IsAncestor {
+		t.Error("HEAD~2 should be ancestor of HEAD")
+	}
+
+	// HEAD is not ancestor of first commit
+	result, err = client.IsAncestor("HEAD", "HEAD~2")
+	if err != nil {
+		t.Fatalf("IsAncestor failed: %v", err)
+	}
+	if result.IsAncestor {
+		t.Error("HEAD should not be ancestor of HEAD~2")
+	}
+}
+
+func TestCommitsBetween(t *testing.T) {
+	repoPath, cleanup := createTestRepo(t)
+	defer cleanup()
+
+	client, err := NewGitClient(repoPath, "")
+	if err != nil {
+		t.Fatalf("NewGitClient failed: %v", err)
+	}
+
+	result, err := client.CommitsBetween("HEAD~2", "HEAD", 10)
+	if err != nil {
+		t.Fatalf("CommitsBetween failed: %v", err)
+	}
+
+	// Should have 2 commits (HEAD~1 and HEAD, exclusive of HEAD~2)
+	if result.Count != 2 {
+		t.Errorf("count = %d, want 2", result.Count)
+	}
+}
+
+func TestListBranches(t *testing.T) {
+	repoPath, cleanup := createTestRepo(t)
+	defer cleanup()
+
+	client, err := NewGitClient(repoPath, "")
+	if err != nil {
+		t.Fatalf("NewGitClient failed: %v", err)
+	}
+
+	result, err := client.ListBranches(false)
+	if err != nil {
+		t.Fatalf("ListBranches failed: %v", err)
+	}
+
+	if result.Total < 1 {
+		t.Error("expected at least one branch")
+	}
+
+	foundMaster := false
+	for _, b := range result.Branches {
+		if b.Name == "master" {
+			foundMaster = true
+			if !b.IsHead {
+				t.Error("master should be HEAD")
+			}
+		}
+	}
+	if !foundMaster {
+		t.Error("expected master branch")
+	}
+}
+
+func TestSearchCommits(t *testing.T) {
+	repoPath, cleanup := createTestRepo(t)
+	defer cleanup()
+
+	client, err := NewGitClient(repoPath, "")
+	if err != nil {
+		t.Fatalf("NewGitClient failed: %v", err)
+	}
+
+	result, err := client.SearchCommits("HEAD", "README", 10)
+	if err != nil {
+		t.Fatalf("SearchCommits failed: %v", err)
+	}
+
+	if result.Count < 1 {
+		t.Error("expected at least one match for 'README'")
+	}
+
+	// Search with no matches
+	result, err = client.SearchCommits("HEAD", "nonexistent-query-xyz", 10)
+	if err != nil {
+		t.Fatalf("SearchCommits for no match failed: %v", err)
+	}
+	if result.Count != 0 {
+		t.Errorf("count = %d, want 0", result.Count)
+	}
+}

internal/gitexplorer/format.go

@@ -0,0 +1,195 @@
+package gitexplorer
+
+import (
+	"fmt"
+	"strings"
+)
+
+// FormatResolveResult formats a ResolveResult as markdown.
+func FormatResolveResult(r *ResolveResult) string {
+	var sb strings.Builder
+	sb.WriteString(fmt.Sprintf("**Ref:** %s\n", r.Ref))
+	sb.WriteString(fmt.Sprintf("**Type:** %s\n", r.Type))
+	sb.WriteString(fmt.Sprintf("**Commit:** %s\n", r.Commit))
+	return sb.String()
+}
+
+// FormatLogEntries formats a slice of LogEntry as markdown.
+func FormatLogEntries(entries []LogEntry) string {
+	if len(entries) == 0 {
+		return "No commits found."
+	}
+
+	var sb strings.Builder
+	sb.WriteString(fmt.Sprintf("## Commit Log (%d commits)\n\n", len(entries)))
+
+	for _, e := range entries {
+		sb.WriteString(fmt.Sprintf("### %s %s\n", e.ShortHash, e.Subject))
+		sb.WriteString(fmt.Sprintf("**Author:** %s <%s>\n", e.Author, e.Email))
+		sb.WriteString(fmt.Sprintf("**Date:** %s\n\n", e.Date.Format("2006-01-02 15:04:05")))
+	}
+
+	return sb.String()
+}
+
+// FormatCommitInfo formats a CommitInfo as markdown.
+func FormatCommitInfo(info *CommitInfo) string {
+	var sb strings.Builder
+	sb.WriteString("## Commit Details\n\n")
+	sb.WriteString(fmt.Sprintf("**Hash:** %s\n", info.Hash))
+	sb.WriteString(fmt.Sprintf("**Author:** %s <%s>\n", info.Author, info.Email))
+	sb.WriteString(fmt.Sprintf("**Date:** %s\n", info.Date.Format("2006-01-02 15:04:05")))
+	sb.WriteString(fmt.Sprintf("**Committer:** %s\n", info.Committer))
+	sb.WriteString(fmt.Sprintf("**Commit Date:** %s\n", info.CommitDate.Format("2006-01-02 15:04:05")))
+
+	if len(info.Parents) > 0 {
+		sb.WriteString(fmt.Sprintf("**Parents:** %s\n", strings.Join(info.Parents, ", ")))
+	}
+
+	if info.Stats != nil {
+		sb.WriteString(fmt.Sprintf("**Changes:** %d file(s), +%d -%d\n",
+			info.Stats.FilesChanged, info.Stats.Additions, info.Stats.Deletions))
+	}
+
+	sb.WriteString("\n### Message\n\n")
+	sb.WriteString("```\n")
+	sb.WriteString(info.Message)
+	if !strings.HasSuffix(info.Message, "\n") {
+		sb.WriteString("\n")
+	}
+	sb.WriteString("```\n")
+
+	return sb.String()
+}
+
+// FormatDiffResult formats a DiffResult as markdown.
+func FormatDiffResult(r *DiffResult) string {
+	if len(r.Files) == 0 {
+		return "No files changed."
+	}
+
+	var sb strings.Builder
+	sb.WriteString(fmt.Sprintf("## Files Changed (%d files)\n\n", len(r.Files)))
+	sb.WriteString(fmt.Sprintf("**From:** %s\n", r.FromCommit[:7]))
+	sb.WriteString(fmt.Sprintf("**To:** %s\n\n", r.ToCommit[:7]))
+
+	sb.WriteString("| Status | Path | Changes |\n")
+	sb.WriteString("|--------|------|--------|\n")
+
+	for _, f := range r.Files {
+		path := f.Path
+		if f.OldPath != "" {
+			path = fmt.Sprintf("%s → %s", f.OldPath, f.Path)
+		}
+		changes := fmt.Sprintf("+%d -%d", f.Additions, f.Deletions)
+		sb.WriteString(fmt.Sprintf("| %s | %s | %s |\n", f.Status, path, changes))
+	}
+
+	return sb.String()
+}
+
+// FormatFileContent formats a FileContent as markdown.
+func FormatFileContent(c *FileContent) string {
+	var sb strings.Builder
+	sb.WriteString(fmt.Sprintf("## File: %s\n\n", c.Path))
+	sb.WriteString(fmt.Sprintf("**Commit:** %s\n", c.Commit[:7]))
+	sb.WriteString(fmt.Sprintf("**Size:** %d bytes\n\n", c.Size))
+
+	// Determine language hint from extension
+	ext := ""
+	if idx := strings.LastIndex(c.Path, "."); idx != -1 {
+		ext = c.Path[idx+1:]
+	}
+
+	sb.WriteString(fmt.Sprintf("```%s\n", ext))
+	sb.WriteString(c.Content)
+	if !strings.HasSuffix(c.Content, "\n") {
+		sb.WriteString("\n")
+	}
+	sb.WriteString("```\n")
+
+	return sb.String()
+}
+
+// FormatAncestryResult formats an AncestryResult as markdown.
+func FormatAncestryResult(r *AncestryResult) string {
+	var sb strings.Builder
+	sb.WriteString("## Ancestry Check\n\n")
+	sb.WriteString(fmt.Sprintf("**Ancestor:** %s\n", r.Ancestor[:7]))
+	sb.WriteString(fmt.Sprintf("**Descendant:** %s\n", r.Descendant[:7]))
+
+	if r.IsAncestor {
+		sb.WriteString("\n✓ **Yes**, the first commit is an ancestor of the second.\n")
+	} else {
+		sb.WriteString("\n✗ **No**, the first commit is not an ancestor of the second.\n")
+	}
+
+	return sb.String()
+}
+
+// FormatCommitRange formats a CommitRange as markdown.
+func FormatCommitRange(r *CommitRange) string {
+	if r.Count == 0 {
+		return "No commits in range."
+	}
+
+	var sb strings.Builder
+	sb.WriteString(fmt.Sprintf("## Commits Between (%d commits)\n\n", r.Count))
+	sb.WriteString(fmt.Sprintf("**From:** %s (exclusive)\n", r.FromCommit[:7]))
+	sb.WriteString(fmt.Sprintf("**To:** %s (inclusive)\n\n", r.ToCommit[:7]))
+
+	for _, e := range r.Commits {
+		sb.WriteString(fmt.Sprintf("- **%s** %s (%s)\n", e.ShortHash, e.Subject, e.Author))
+	}
+
+	return sb.String()
+}
+
+// FormatBranchList formats a BranchList as markdown.
+func FormatBranchList(r *BranchList) string {
+	if r.Total == 0 {
+		return "No branches found."
+	}
+
+	var sb strings.Builder
+	sb.WriteString(fmt.Sprintf("## Branches (%d total)\n\n", r.Total))
+
+	if r.Current != "" {
+		sb.WriteString(fmt.Sprintf("**Current branch:** %s\n\n", r.Current))
+	}
+
+	sb.WriteString("| Branch | Commit | Type |\n")
+	sb.WriteString("|--------|--------|------|\n")
+
+	for _, b := range r.Branches {
+		branchType := "local"
+		if b.IsRemote {
+			branchType = "remote"
+		}
+		marker := ""
+		if b.IsHead {
+			marker = " ✓"
+		}
+		sb.WriteString(fmt.Sprintf("| %s%s | %s | %s |\n", b.Name, marker, b.Commit[:7], branchType))
+	}
+
+	return sb.String()
+}
+
+// FormatSearchResult formats a SearchResult as markdown.
+func FormatSearchResult(r *SearchResult) string {
+	if r.Count == 0 {
+		return fmt.Sprintf("No commits found matching '%s'.", r.Query)
+	}
+
+	var sb strings.Builder
+	sb.WriteString(fmt.Sprintf("## Search Results for '%s' (%d matches)\n\n", r.Query, r.Count))
+
+	for _, e := range r.Commits {
+		sb.WriteString(fmt.Sprintf("### %s %s\n", e.ShortHash, e.Subject))
+		sb.WriteString(fmt.Sprintf("**Author:** %s <%s>\n", e.Author, e.Email))
+		sb.WriteString(fmt.Sprintf("**Date:** %s\n\n", e.Date.Format("2006-01-02 15:04:05")))
+	}
+
+	return sb.String()
+}

internal/gitexplorer/handlers.go

@@ -0,0 +1,440 @@
+package gitexplorer
+
+import (
+	"context"
+	"fmt"
+
+	"git.t-juice.club/torjus/labmcp/internal/mcp"
+)
+
+// RegisterHandlers registers all git-explorer tool handlers on the MCP server.
+func RegisterHandlers(server *mcp.Server, client *GitClient) {
+	server.RegisterTool(resolveRefTool(), makeResolveRefHandler(client))
+	server.RegisterTool(getLogTool(), makeGetLogHandler(client))
+	server.RegisterTool(getCommitInfoTool(), makeGetCommitInfoHandler(client))
+	server.RegisterTool(getDiffFilesTool(), makeGetDiffFilesHandler(client))
+	server.RegisterTool(getFileAtCommitTool(), makeGetFileAtCommitHandler(client))
+	server.RegisterTool(isAncestorTool(), makeIsAncestorHandler(client))
+	server.RegisterTool(commitsBetweenTool(), makeCommitsBetweenHandler(client))
+	server.RegisterTool(listBranchesTool(), makeListBranchesHandler(client))
+	server.RegisterTool(searchCommitsTool(), makeSearchCommitsHandler(client))
+}
+
+// Tool definitions
+
+func resolveRefTool() mcp.Tool {
+	return mcp.Tool{
+		Name:        "resolve_ref",
+		Description: "Resolve a git ref (branch, tag, or commit hash) to its full commit hash",
+		InputSchema: mcp.InputSchema{
+			Type: "object",
+			Properties: map[string]mcp.Property{
+				"ref": {
+					Type:        "string",
+					Description: "Git ref to resolve (e.g., 'main', 'v1.0.0', 'HEAD', commit hash)",
+				},
+			},
+			Required: []string{"ref"},
+		},
+	}
+}
+
+func getLogTool() mcp.Tool {
+	return mcp.Tool{
+		Name:        "get_log",
+		Description: "Get commit log starting from a ref, with optional filters",
+		InputSchema: mcp.InputSchema{
+			Type: "object",
+			Properties: map[string]mcp.Property{
+				"ref": {
+					Type:        "string",
+					Description: "Starting ref for the log (default: HEAD)",
+				},
+				"limit": {
+					Type:        "integer",
+					Description: fmt.Sprintf("Maximum number of commits to return (default: 20, max: %d)", Limits.MaxLogEntries),
+					Default:     20,
+				},
+				"author": {
+					Type:        "string",
+					Description: "Filter by author name or email (substring match)",
+				},
+				"since": {
+					Type:        "string",
+					Description: "Stop log at this ref (exclusive)",
+				},
+				"path": {
+					Type:        "string",
+					Description: "Filter commits that affect this path",
+				},
+			},
+		},
+	}
+}
+
+func getCommitInfoTool() mcp.Tool {
+	return mcp.Tool{
+		Name:        "get_commit_info",
+		Description: "Get full details for a specific commit including message, author, and optionally file statistics",
+		InputSchema: mcp.InputSchema{
+			Type: "object",
+			Properties: map[string]mcp.Property{
+				"ref": {
+					Type:        "string",
+					Description: "Commit ref (hash, branch, tag, or HEAD)",
+				},
+				"include_stats": {
+					Type:        "boolean",
+					Description: "Include file change statistics (default: true)",
+					Default:     true,
+				},
+			},
+			Required: []string{"ref"},
+		},
+	}
+}
+
+func getDiffFilesTool() mcp.Tool {
+	return mcp.Tool{
+		Name:        "get_diff_files",
+		Description: "Get list of files changed between two commits with change type and line counts",
+		InputSchema: mcp.InputSchema{
+			Type: "object",
+			Properties: map[string]mcp.Property{
+				"from_ref": {
+					Type:        "string",
+					Description: "Starting commit ref (the older commit)",
+				},
+				"to_ref": {
+					Type:        "string",
+					Description: "Ending commit ref (the newer commit)",
+				},
+			},
+			Required: []string{"from_ref", "to_ref"},
+		},
+	}
+}
+
+func getFileAtCommitTool() mcp.Tool {
+	return mcp.Tool{
+		Name:        "get_file_at_commit",
+		Description: fmt.Sprintf("Get the contents of a file at a specific commit (max %dKB)", Limits.MaxFileContent/1024),
+		InputSchema: mcp.InputSchema{
+			Type: "object",
+			Properties: map[string]mcp.Property{
+				"ref": {
+					Type:        "string",
+					Description: "Commit ref (hash, branch, tag, or HEAD)",
+				},
+				"path": {
+					Type:        "string",
+					Description: "Path to the file relative to repository root",
+				},
+			},
+			Required: []string{"ref", "path"},
+		},
+	}
+}
+
+func isAncestorTool() mcp.Tool {
+	return mcp.Tool{
+		Name:        "is_ancestor",
+		Description: "Check if one commit is an ancestor of another",
+		InputSchema: mcp.InputSchema{
+			Type: "object",
+			Properties: map[string]mcp.Property{
+				"ancestor": {
+					Type:        "string",
+					Description: "Potential ancestor commit ref",
+				},
+				"descendant": {
+					Type:        "string",
+					Description: "Potential descendant commit ref",
+				},
+			},
+			Required: []string{"ancestor", "descendant"},
+		},
+	}
+}
+
+func commitsBetweenTool() mcp.Tool {
+	return mcp.Tool{
+		Name:        "commits_between",
+		Description: "Get all commits between two refs (from is exclusive, to is inclusive)",
+		InputSchema: mcp.InputSchema{
+			Type: "object",
+			Properties: map[string]mcp.Property{
+				"from_ref": {
+					Type:        "string",
+					Description: "Starting commit ref (exclusive - commits after this)",
+				},
+				"to_ref": {
+					Type:        "string",
+					Description: "Ending commit ref (inclusive - up to and including this)",
+				},
+				"limit": {
+					Type:        "integer",
+					Description: fmt.Sprintf("Maximum number of commits (default: %d)", Limits.MaxLogEntries),
+					Default:     Limits.MaxLogEntries,
+				},
+			},
+			Required: []string{"from_ref", "to_ref"},
+		},
+	}
+}
+
+func listBranchesTool() mcp.Tool {
+	return mcp.Tool{
+		Name:        "list_branches",
+		Description: "List all branches in the repository",
+		InputSchema: mcp.InputSchema{
+			Type: "object",
+			Properties: map[string]mcp.Property{
+				"include_remote": {
+					Type:        "boolean",
+					Description: "Include remote-tracking branches (default: false)",
+					Default:     false,
+				},
+			},
+		},
+	}
+}
+
+func searchCommitsTool() mcp.Tool {
+	return mcp.Tool{
+		Name:        "search_commits",
+		Description: "Search commit messages for a pattern (case-insensitive)",
+		InputSchema: mcp.InputSchema{
+			Type: "object",
+			Properties: map[string]mcp.Property{
+				"query": {
+					Type:        "string",
+					Description: "Search pattern to match in commit messages",
+				},
+				"ref": {
+					Type:        "string",
+					Description: "Starting ref for the search (default: HEAD)",
+				},
+				"limit": {
+					Type:        "integer",
+					Description: fmt.Sprintf("Maximum number of results (default: 20, max: %d)", Limits.MaxSearchResult),
+					Default:     20,
+				},
+			},
+			Required: []string{"query"},
+		},
+	}
+}
+
+// Handler constructors
+
+func makeResolveRefHandler(client *GitClient) mcp.ToolHandler {
+	return func(ctx context.Context, args map[string]interface{}) (mcp.CallToolResult, error) {
+		ref, _ := args["ref"].(string)
+		if ref == "" {
+			return mcp.ErrorContent(fmt.Errorf("ref is required")), nil
+		}
+
+		result, err := client.ResolveRef(ref)
+		if err != nil {
+			return mcp.ErrorContent(err), nil
+		}
+
+		return mcp.CallToolResult{
+			Content: []mcp.Content{mcp.TextContent(FormatResolveResult(result))},
+		}, nil
+	}
+}
+
+func makeGetLogHandler(client *GitClient) mcp.ToolHandler {
+	return func(ctx context.Context, args map[string]interface{}) (mcp.CallToolResult, error) {
+		ref := "HEAD"
+		if r, ok := args["ref"].(string); ok && r != "" {
+			ref = r
+		}
+
+		limit := 20
+		if l, ok := args["limit"].(float64); ok && l > 0 {
+			limit = int(l)
+		}
+
+		author, _ := args["author"].(string)
+		since, _ := args["since"].(string)
+		path, _ := args["path"].(string)
+
+		entries, err := client.GetLog(ref, limit, author, since, path)
+		if err != nil {
+			return mcp.ErrorContent(err), nil
+		}
+
+		return mcp.CallToolResult{
+			Content: []mcp.Content{mcp.TextContent(FormatLogEntries(entries))},
+		}, nil
+	}
+}
+
+func makeGetCommitInfoHandler(client *GitClient) mcp.ToolHandler {
+	return func(ctx context.Context, args map[string]interface{}) (mcp.CallToolResult, error) {
+		ref, _ := args["ref"].(string)
+		if ref == "" {
+			return mcp.ErrorContent(fmt.Errorf("ref is required")), nil
+		}
+
+		includeStats := true
+		if s, ok := args["include_stats"].(bool); ok {
+			includeStats = s
+		}
+
+		info, err := client.GetCommitInfo(ref, includeStats)
+		if err != nil {
+			return mcp.ErrorContent(err), nil
+		}
+
+		return mcp.CallToolResult{
+			Content: []mcp.Content{mcp.TextContent(FormatCommitInfo(info))},
+		}, nil
+	}
+}
+
+func makeGetDiffFilesHandler(client *GitClient) mcp.ToolHandler {
+	return func(ctx context.Context, args map[string]interface{}) (mcp.CallToolResult, error) {
+		fromRef, _ := args["from_ref"].(string)
+		if fromRef == "" {
+			return mcp.ErrorContent(fmt.Errorf("from_ref is required")), nil
+		}
+
+		toRef, _ := args["to_ref"].(string)
+		if toRef == "" {
+			return mcp.ErrorContent(fmt.Errorf("to_ref is required")), nil
+		}
+
+		result, err := client.GetDiffFiles(fromRef, toRef)
+		if err != nil {
+			return mcp.ErrorContent(err), nil
+		}
+
+		return mcp.CallToolResult{
+			Content: []mcp.Content{mcp.TextContent(FormatDiffResult(result))},
+		}, nil
+	}
+}
+
+func makeGetFileAtCommitHandler(client *GitClient) mcp.ToolHandler {
+	return func(ctx context.Context, args map[string]interface{}) (mcp.CallToolResult, error) {
+		ref, _ := args["ref"].(string)
+		if ref == "" {
+			return mcp.ErrorContent(fmt.Errorf("ref is required")), nil
+		}
+
+		path, _ := args["path"].(string)
+		if path == "" {
+			return mcp.ErrorContent(fmt.Errorf("path is required")), nil
+		}
+
+		content, err := client.GetFileAtCommit(ref, path)
+		if err != nil {
+			return mcp.ErrorContent(err), nil
+		}
+
+		return mcp.CallToolResult{
+			Content: []mcp.Content{mcp.TextContent(FormatFileContent(content))},
+		}, nil
+	}
+}
+
+func makeIsAncestorHandler(client *GitClient) mcp.ToolHandler {
+	return func(ctx context.Context, args map[string]interface{}) (mcp.CallToolResult, error) {
+		ancestor, _ := args["ancestor"].(string)
+		if ancestor == "" {
+			return mcp.ErrorContent(fmt.Errorf("ancestor is required")), nil
+		}
+
+		descendant, _ := args["descendant"].(string)
+		if descendant == "" {
+			return mcp.ErrorContent(fmt.Errorf("descendant is required")), nil
+		}
+
+		result, err := client.IsAncestor(ancestor, descendant)
+		if err != nil {
+			return mcp.ErrorContent(err), nil
+		}
+
+		return mcp.CallToolResult{
+			Content: []mcp.Content{mcp.TextContent(FormatAncestryResult(result))},
+		}, nil
+	}
+}
+
+func makeCommitsBetweenHandler(client *GitClient) mcp.ToolHandler {
+	return func(ctx context.Context, args map[string]interface{}) (mcp.CallToolResult, error) {
+		fromRef, _ := args["from_ref"].(string)
+		if fromRef == "" {
+			return mcp.ErrorContent(fmt.Errorf("from_ref is required")), nil
+		}
+
+		toRef, _ := args["to_ref"].(string)
+		if toRef == "" {
+			return mcp.ErrorContent(fmt.Errorf("to_ref is required")), nil
+		}
+
+		limit := Limits.MaxLogEntries
+		if l, ok := args["limit"].(float64); ok && l > 0 {
+			limit = int(l)
+		}
+
+		result, err := client.CommitsBetween(fromRef, toRef, limit)
+		if err != nil {
+			return mcp.ErrorContent(err), nil
+		}
+
+		return mcp.CallToolResult{
+			Content: []mcp.Content{mcp.TextContent(FormatCommitRange(result))},
+		}, nil
+	}
+}
+
+func makeListBranchesHandler(client *GitClient) mcp.ToolHandler {
+	return func(ctx context.Context, args map[string]interface{}) (mcp.CallToolResult, error) {
+		includeRemote := false
+		if r, ok := args["include_remote"].(bool); ok {
+			includeRemote = r
+		}
+
+		result, err := client.ListBranches(includeRemote)
+		if err != nil {
+			return mcp.ErrorContent(err), nil
+		}
+
+		return mcp.CallToolResult{
+			Content: []mcp.Content{mcp.TextContent(FormatBranchList(result))},
+		}, nil
+	}
+}
+
+func makeSearchCommitsHandler(client *GitClient) mcp.ToolHandler {
+	return func(ctx context.Context, args map[string]interface{}) (mcp.CallToolResult, error) {
+		query, _ := args["query"].(string)
+		if query == "" {
+			return mcp.ErrorContent(fmt.Errorf("query is required")), nil
+		}
+
+		ref := "HEAD"
+		if r, ok := args["ref"].(string); ok && r != "" {
+			ref = r
+		}
+
+		limit := 20
+		if l, ok := args["limit"].(float64); ok && l > 0 {
+			limit = int(l)
+		}
+
+		result, err := client.SearchCommits(ref, query, limit)
+		if err != nil {
+			return mcp.ErrorContent(err), nil
+		}
+
+		return mcp.CallToolResult{
+			Content: []mcp.Content{mcp.TextContent(FormatSearchResult(result))},
+		}, nil
+	}
+}

internal/gitexplorer/types.go

@@ -0,0 +1,121 @@
+package gitexplorer
+
+import (
+	"time"
+)
+
+// ResolveResult contains the result of resolving a ref to a commit.
+type ResolveResult struct {
+	Ref    string `json:"ref"`
+	Commit string `json:"commit"`
+	Type   string `json:"type"` // "branch", "tag", "commit"
+}
+
+// LogEntry represents a single commit in the log.
+type LogEntry struct {
+	Hash      string    `json:"hash"`
+	ShortHash string    `json:"short_hash"`
+	Author    string    `json:"author"`
+	Email     string    `json:"email"`
+	Date      time.Time `json:"date"`
+	Subject   string    `json:"subject"`
+}
+
+// CommitInfo contains full details about a commit.
+type CommitInfo struct {
+	Hash       string     `json:"hash"`
+	Author     string     `json:"author"`
+	Email      string     `json:"email"`
+	Date       time.Time  `json:"date"`
+	Committer  string     `json:"committer"`
+	CommitDate time.Time  `json:"commit_date"`
+	Message    string     `json:"message"`
+	Parents    []string   `json:"parents"`
+	Stats      *FileStats `json:"stats,omitempty"`
+}
+
+// FileStats contains statistics about file changes.
+type FileStats struct {
+	FilesChanged int `json:"files_changed"`
+	Additions    int `json:"additions"`
+	Deletions    int `json:"deletions"`
+}
+
+// DiffFile represents a file changed between two commits.
+type DiffFile struct {
+	Path      string `json:"path"`
+	OldPath   string `json:"old_path,omitempty"` // For renames
+	Status    string `json:"status"`             // "added", "modified", "deleted", "renamed"
+	Additions int    `json:"additions"`
+	Deletions int    `json:"deletions"`
+}
+
+// DiffResult contains the list of files changed between two commits.
+type DiffResult struct {
+	FromCommit string     `json:"from_commit"`
+	ToCommit   string     `json:"to_commit"`
+	Files      []DiffFile `json:"files"`
+}
+
+// FileContent represents the content of a file at a specific commit.
+type FileContent struct {
+	Path    string `json:"path"`
+	Commit  string `json:"commit"`
+	Size    int64  `json:"size"`
+	Content string `json:"content"`
+}
+
+// AncestryResult contains the result of an ancestry check.
+type AncestryResult struct {
+	Ancestor   string `json:"ancestor"`
+	Descendant string `json:"descendant"`
+	IsAncestor bool   `json:"is_ancestor"`
+}
+
+// CommitRange represents commits between two refs.
+type CommitRange struct {
+	FromCommit string     `json:"from_commit"`
+	ToCommit   string     `json:"to_commit"`
+	Commits    []LogEntry `json:"commits"`
+	Count      int        `json:"count"`
+}
+
+// Branch represents a git branch.
+type Branch struct {
+	Name     string `json:"name"`
+	Commit   string `json:"commit"`
+	IsRemote bool   `json:"is_remote"`
+	IsHead   bool   `json:"is_head"`
+	Upstream string `json:"upstream,omitempty"`
+	AheadBy  int    `json:"ahead_by,omitempty"`
+	BehindBy int    `json:"behind_by,omitempty"`
+}
+
+// BranchList contains the list of branches.
+type BranchList struct {
+	Branches []Branch `json:"branches"`
+	Current  string   `json:"current"`
+	Total    int      `json:"total"`
+}
+
+// SearchResult represents a commit matching a search query.
+type SearchResult struct {
+	Commits []LogEntry `json:"commits"`
+	Query   string     `json:"query"`
+	Count   int        `json:"count"`
+}
+
+// Limits defines the maximum values for various operations.
+var Limits = struct {
+	MaxFileContent  int64 // Maximum file size in bytes
+	MaxLogEntries   int   // Maximum commit log entries
+	MaxBranches     int   // Maximum branches to list
+	MaxDiffFiles    int   // Maximum files in diff
+	MaxSearchResult int   // Maximum search results
+}{
+	MaxFileContent:  100 * 1024, // 100KB
+	MaxLogEntries:   100,
+	MaxBranches:     500,
+	MaxDiffFiles:    1000,
+	MaxSearchResult: 100,
+}

internal/gitexplorer/validation.go

@@ -0,0 +1,57 @@
+package gitexplorer
+
+import (
+	"errors"
+	"path/filepath"
+	"slices"
+	"strings"
+)
+
+var (
+	// ErrPathTraversal is returned when a path attempts to traverse outside the repository.
+	ErrPathTraversal = errors.New("path traversal not allowed")
+	// ErrAbsolutePath is returned when an absolute path is provided.
+	ErrAbsolutePath = errors.New("absolute paths not allowed")
+	// ErrNullByte is returned when a path contains null bytes.
+	ErrNullByte = errors.New("null bytes not allowed in path")
+	// ErrEmptyPath is returned when a path is empty.
+	ErrEmptyPath = errors.New("path cannot be empty")
+)
+
+// ValidatePath validates a file path for security.
+// It rejects:
+// - Absolute paths
+// - Paths containing null bytes
+// - Paths that attempt directory traversal (contain "..")
+// - Empty paths
+func ValidatePath(path string) error {
+	if path == "" {
+		return ErrEmptyPath
+	}
+
+	// Check for null bytes
+	if strings.Contains(path, "\x00") {
+		return ErrNullByte
+	}
+
+	// Check for absolute paths
+	if filepath.IsAbs(path) {
+		return ErrAbsolutePath
+	}
+
+	// Clean the path and check for traversal
+	cleaned := filepath.Clean(path)
+
+	// Check if cleaned path starts with ".."
+	if strings.HasPrefix(cleaned, "..") {
+		return ErrPathTraversal
+	}
+
+	// Check for ".." components in the path
+	parts := strings.Split(cleaned, string(filepath.Separator))
+	if slices.Contains(parts, "..") {
+		return ErrPathTraversal
+	}
+
+	return nil
+}

internal/gitexplorer/validation_test.go

@@ -0,0 +1,91 @@
+package gitexplorer
+
+import (
+	"testing"
+)
+
+func TestValidatePath(t *testing.T) {
+	tests := []struct {
+		name    string
+		path    string
+		wantErr error
+	}{
+		// Valid paths
+		{
+			name:    "simple file",
+			path:    "README.md",
+			wantErr: nil,
+		},
+		{
+			name:    "nested file",
+			path:    "internal/gitexplorer/types.go",
+			wantErr: nil,
+		},
+		{
+			name:    "file with dots",
+			path:    "file.test.go",
+			wantErr: nil,
+		},
+		{
+			name:    "current dir prefix",
+			path:    "./README.md",
+			wantErr: nil,
+		},
+		{
+			name:    "deeply nested",
+			path:    "a/b/c/d/e/f/g.txt",
+			wantErr: nil,
+		},
+
+		// Invalid paths
+		{
+			name:    "empty path",
+			path:    "",
+			wantErr: ErrEmptyPath,
+		},
+		{
+			name:    "absolute path unix",
+			path:    "/etc/passwd",
+			wantErr: ErrAbsolutePath,
+		},
+		{
+			name:    "parent dir traversal simple",
+			path:    "../secret.txt",
+			wantErr: ErrPathTraversal,
+		},
+		{
+			name:    "parent dir traversal nested",
+			path:    "foo/../../../etc/passwd",
+			wantErr: ErrPathTraversal,
+		},
+		{
+			name:    "parent dir traversal in middle",
+			path:    "foo/bar/../../../secret",
+			wantErr: ErrPathTraversal,
+		},
+		{
+			name:    "null byte",
+			path:    "file\x00.txt",
+			wantErr: ErrNullByte,
+		},
+		{
+			name:    "null byte in middle",
+			path:    "foo/bar\x00baz/file.txt",
+			wantErr: ErrNullByte,
+		},
+		{
+			name:    "double dot only",
+			path:    "..",
+			wantErr: ErrPathTraversal,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			err := ValidatePath(tt.path)
+			if err != tt.wantErr {
+				t.Errorf("ValidatePath(%q) = %v, want %v", tt.path, err, tt.wantErr)
+			}
+		})
+	}
+}

internal/mcp/server.go

@@ -118,6 +118,27 @@ This ensures option documentation matches the home-manager version the project a
 	}
 }
 
+// DefaultGitExplorerConfig returns the default configuration for the git-explorer server.
+func DefaultGitExplorerConfig() ServerConfig {
+	return ServerConfig{
+		Name:    "git-explorer",
+		Version: "0.1.0",
+		Mode:    ModeCustom,
+		Instructions: `Git Explorer MCP Server - Read-only access to git repository information.
+
+Tools for exploring git repositories:
+- Resolve refs (branches, tags, commits) to commit hashes
+- View commit logs with filtering by author, path, or range
+- Get full commit details including file change statistics
+- Compare commits to see which files changed
+- Read file contents at any commit
+- Check ancestry relationships between commits
+- Search commit messages
+
+All operations are read-only and will never modify the repository.`,
+	}
+}
+
 // Server is an MCP server that handles JSON-RPC requests.
 type Server struct {
 	store       database.Store

nix/git-explorer-module.nix

@@ -0,0 +1,141 @@
+{ config, lib, pkgs, ... }:
+
+let
+  cfg = config.services.git-explorer;
+
+  mkHttpFlags = httpCfg: lib.concatStringsSep " " ([
+    "--transport http"
+    "--http-address '${httpCfg.address}'"
+    "--http-endpoint '${httpCfg.endpoint}'"
+    "--session-ttl '${httpCfg.sessionTTL}'"
+  ] ++ lib.optionals (httpCfg.allowedOrigins != []) (
+    map (origin: "--allowed-origins '${origin}'") httpCfg.allowedOrigins
+  ) ++ lib.optionals httpCfg.tls.enable [
+    "--tls-cert '${httpCfg.tls.certFile}'"
+    "--tls-key '${httpCfg.tls.keyFile}'"
+  ]);
+in
+{
+  options.services.git-explorer = {
+    enable = lib.mkEnableOption "Git Explorer MCP server";
+
+    package = lib.mkPackageOption pkgs "git-explorer" { };
+
+    repoPath = lib.mkOption {
+      type = lib.types.str;
+      description = "Path to the git repository to serve.";
+    };
+
+    defaultRemote = lib.mkOption {
+      type = lib.types.str;
+      default = "origin";
+      description = "Default remote name for ref resolution.";
+    };
+
+    http = {
+      address = lib.mkOption {
+        type = lib.types.str;
+        default = "127.0.0.1:8085";
+        description = "HTTP listen address for the MCP server.";
+      };
+
+      endpoint = lib.mkOption {
+        type = lib.types.str;
+        default = "/mcp";
+        description = "HTTP endpoint path for MCP requests.";
+      };
+
+      allowedOrigins = lib.mkOption {
+        type = lib.types.listOf lib.types.str;
+        default = [ ];
+        description = "Allowed Origin headers for CORS.";
+      };
+
+      sessionTTL = lib.mkOption {
+        type = lib.types.str;
+        default = "30m";
+        description = "Session TTL for HTTP transport.";
+      };
+
+      tls = {
+        enable = lib.mkEnableOption "TLS for HTTP transport";
+
+        certFile = lib.mkOption {
+          type = lib.types.nullOr lib.types.path;
+          default = null;
+          description = "Path to TLS certificate file.";
+        };
+
+        keyFile = lib.mkOption {
+          type = lib.types.nullOr lib.types.path;
+          default = null;
+          description = "Path to TLS private key file.";
+        };
+      };
+    };
+
+    openFirewall = lib.mkOption {
+      type = lib.types.bool;
+      default = false;
+      description = "Whether to open the firewall for the MCP HTTP server.";
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    assertions = [
+      {
+        assertion = !cfg.http.tls.enable || (cfg.http.tls.certFile != null && cfg.http.tls.keyFile != null);
+        message = "services.git-explorer.http.tls: both certFile and keyFile must be set when TLS is enabled";
+      }
+    ];
+
+    systemd.services.git-explorer = {
+      description = "Git Explorer MCP Server";
+      wantedBy = [ "multi-user.target" ];
+      after = [ "network.target" ];
+
+      environment = {
+        GIT_REPO_PATH = cfg.repoPath;
+        GIT_DEFAULT_REMOTE = cfg.defaultRemote;
+      };
+
+      script = let
+        httpFlags = mkHttpFlags cfg.http;
+      in ''
+        exec ${cfg.package}/bin/git-explorer serve ${httpFlags}
+      '';
+
+      serviceConfig = {
+        Type = "simple";
+        DynamicUser = true;
+        Restart = "on-failure";
+        RestartSec = "5s";
+
+        # Hardening
+        NoNewPrivileges = true;
+        ProtectSystem = "strict";
+        ProtectHome = "read-only";
+        PrivateTmp = true;
+        PrivateDevices = true;
+        ProtectKernelTunables = true;
+        ProtectKernelModules = true;
+        ProtectControlGroups = true;
+        RestrictNamespaces = true;
+        RestrictRealtime = true;
+        RestrictSUIDSGID = true;
+        MemoryDenyWriteExecute = true;
+        LockPersonality = true;
+
+        # Read-only access to repo path
+        ReadOnlyPaths = [ cfg.repoPath ];
+      };
+    };
+
+    networking.firewall = lib.mkIf cfg.openFirewall (let
+      addressParts = lib.splitString ":" cfg.http.address;
+      port = lib.toInt (lib.last addressParts);
+    in {
+      allowedTCPPorts = [ port ];
+    });
+  };
+}

nix/package.nix

@@ -9,7 +9,7 @@ buildGoModule {
   inherit pname src;
   version = "0.3.0";
 
-  vendorHash = "sha256-D0KIxQC9ctIAaHBFTvkhBE06uOZwDUcIw8471Ug2doY=";
+  vendorHash = "sha256-XrTtiaQT5br+0ZXz8//rc04GZn/HlQk7l8Nx/+Uil/I=";
 
   subPackages = [ subPackage ];