diff --git a/.github/workflows/calendar.yml b/.github/workflows/calendar.yml
index 046d8e9..6854fe9 100644
--- a/.github/workflows/calendar.yml
+++ b/.github/workflows/calendar.yml
@@ -4,6 +4,7 @@ on:
   schedule:
     - cron: '0 0 * * *'
   workflow_dispatch:
+  pull_request:
 
 jobs:
   update-tournaments:
@@ -30,8 +31,29 @@ jobs:
         run: |
           python _scripts/update_tournaments.py
 
+      - name: Add tournaments diff to summary (pull requests only)
+        if: github.event_name == 'pull_request'
+        run: |
+          diff_output=$(git diff -- _data/tournaments.tsv)
+          if [ -z "$diff_output" ]; then
+            {
+              echo "## Tournament list diff"
+              echo
+              echo "No changes in \\`_data/tournaments.tsv\\`."
+            } >> "$GITHUB_STEP_SUMMARY"
+          else
+            {
+              echo "## Tournament list diff"
+              echo
+              echo '```diff'
+              echo "$diff_output"
+              echo '```'
+            } >> "$GITHUB_STEP_SUMMARY"
+          fi
+
       # Commit all changed files back to the repository
       - uses: stefanzweifel/git-auto-commit-action@v7
+        if: github.event_name != 'pull_request'
         with:
           commit_message: Update tournaments
           file_pattern: '*.tsv'