diff --git a/CLAUDE.md b/CLAUDE.md
index 18e8b54..40ed0c8 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -27,6 +27,11 @@ nix develop
 If config clearly only affects one host, bulding for just the relevant host is enough.
 Otherwise, build both.
 
+If moving things around, you can use `nix eval` before and after changes to check that things remain the same.
+```
+nix eval .#nixosConfigurations.magicman.config.nix.settings.substituters --json | jq
+```
+
 ### Common Operations
 ```bash
 # Check flake without building