diff --git a/.github/workflows/check.yml b/.github/workflows/check.yml
index 06bf69b47..99d238e3c 100644
--- a/.github/workflows/check.yml
+++ b/.github/workflows/check.yml
@@ -23,3 +23,8 @@ jobs:
     
     - name: bundle
       run: moon bundle
+
+    - name: format diff
+      run: |
+        moon fmt
+        git diff