diff --git a/CLAUDE.md b/CLAUDE.md
index 6565e8f..1376a9e 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -157,6 +157,17 @@ Four types of skills. See [CONTRIBUTING.md](CONTRIBUTING.md) for the full taxono
 
 Before creating a PR, adding a skill, or preparing any contribution, you MUST read [CONTRIBUTING.md](CONTRIBUTING.md). It covers accepted change types, the four skill types and their guidelines, `SKILL.md` format rules, and the pre-submission checklist.
 
+## PR Hygiene
+
+Before creating a PR, run these checks:
+
+```bash
+git diff upstream/main --stat HEAD
+git log upstream/main..HEAD --oneline
+```
+
+Show the output and wait for approval. Installation-specific files (group files, .claude/settings.json, local configs) should not be included.
+
 ## Development
 
 Run commands directly — don't tell the user to run them.
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 7a7816a..413e542 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -123,7 +123,8 @@ Test your contribution on a fresh clone before submitting. For skills, run the s
 
 1. **Link related issues.** If your PR resolves an open issue, include `Closes #123` in the description so it's auto-closed on merge.
 2. **Test thoroughly.** Run the feature yourself. For skills, test on a fresh clone.
-3. **Check the right box** in the PR template. Labels are auto-applied based on your selection:
+3. **Check for installation-specific files.** Before creating a PR, verify no installation-specific files are in your diff (see PR Hygiene in CLAUDE.md).
+4. **Check the right box** in the PR template. Labels are auto-applied based on your selection:
 
 | Checkbox | Label |
 |----------|-------|