diff --git a/internal/mcp/server.go b/internal/mcp/server.go
index fbb8e0a..22874d6 100644
--- a/internal/mcp/server.go
+++ b/internal/mcp/server.go
@@ -149,6 +149,15 @@ func (s *Server) handleInitialize(req *Request) *Response {
 			Name:    "nixos-options",
 			Version: "0.1.0",
 		},
+		Instructions: `NixOS Options MCP Server - Search and query NixOS configuration options.
+
+If the current project contains a flake.lock file, you can index the exact nixpkgs revision used by the project:
+1. Read the flake.lock file to find the nixpkgs "rev" field
+2. Call index_revision with that git hash to index options for that specific version
+
+Example: If flake.lock contains "rev": "abc123...", call index_revision with revision "abc123...".
+
+This ensures option documentation matches the nixpkgs version the project actually uses.`,
 	}
 
 	return &Response{
diff --git a/internal/mcp/types.go b/internal/mcp/types.go
index 6cd9674..e80c398 100644
--- a/internal/mcp/types.go
+++ b/internal/mcp/types.go
@@ -51,6 +51,7 @@ type InitializeResult struct {
 	ProtocolVersion string         `json:"protocolVersion"`
 	Capabilities    Capabilities   `json:"capabilities"`
 	ServerInfo      Implementation `json:"serverInfo"`
+	Instructions    string         `json:"instructions,omitempty"`
 }
 
 // Capabilities describes client or server capabilities.