diff --git a/.github/workflows/validate-plugins.yml b/.github/workflows/validate-plugins.yml
new file mode 100644
index 0000000..a08f1d1
--- /dev/null
+++ b/.github/workflows/validate-plugins.yml
@@ -0,0 +1,37 @@
+name: Validate Plugins
+
+on:
+  push:
+    branches: [main]
+    paths:
+      - "plugins/**"
+      - ".claude-plugin/**"
+  pull_request:
+    paths:
+      - "plugins/**"
+      - ".claude-plugin/**"
+
+jobs:
+  validate:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4.3.1
+
+      - name: Install Claude Code
+        run: npm install -g @anthropic-ai/claude-code@2.1.183
+
+      - name: Validate all plugins
+        run: |
+          failed=0
+          for plugin in plugins/*/; do
+            echo "::group::Validating $plugin"
+            if ! claude plugin validate "$plugin" --strict; then
+              echo "::error::Validation failed for $plugin"
+              failed=1
+            fi
+            echo "::endgroup::"
+          done
+          exit $failed
+
+      - name: Validate marketplace manifest
+        run: claude plugin validate . --strict
diff --git a/CLAUDE.md b/CLAUDE.md
index 326ffcd..5018738 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -71,3 +71,13 @@ Common `allowed-tools` patterns: `Bash(git *)`, `Bash(gh *)`, `Bash(npx ccusage*
 - Each plugin has independent semver in `plugin.json`
 - Root marketplace version bumps minor on every plugin release
 - Tags: `{plugin}/v{version}`
+
+### External Dependencies
+
+Always pin external dependencies to an exact, reproducible version — no floating references anywhere in the project.
+
+- **GitHub Actions**: pin `uses:` to a full commit SHA; add the exact patch version as a comment
+  - `actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4.3.1`
+  - To find SHA: `gh api repos/{owner}/{repo}/git/ref/tags/{tag} --jq '.object.sha'`
+- **npm**: use exact version (`@2.1.183`), never a range or bare package name
+- **Any other package manager or tool** (pip, cargo, brew, etc.): same rule — exact version only