diff --git a/.gitea/workflows/diagnose.yaml b/.gitea/workflows/diagnose.yaml
new file mode 100644
index 0000000..994f1cb
--- /dev/null
+++ b/.gitea/workflows/diagnose.yaml
@@ -0,0 +1,26 @@
+
+name: Diagnose GitHub mirror
+
+on:
+  push:
+    branches:
+      - main
+  workflow_dispatch:
+
+jobs:
+  diagnose:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check source and credentials
+        env:
+          GH_TOKEN: ${{ secrets.GH_TOKEN }}
+        run: |
+          set -eu
+          echo "Triggered ref: $GITHUB_REF"
+          echo "Source commit: $GITHUB_SHA"
+          if [ -z "$GH_TOKEN" ]; then
+            echo "ERROR: GH_TOKEN is empty or unavailable"
+            exit 1
+          fi
+          echo "GitHub token is present"
+          git --version