diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index e859e4613..bea5f6eb5 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -1,11 +1,19 @@
 name: Build schemas classes
 
+# A pull request gets the tests, the build and the toolbox tests, so that a
+# reviewer sees whether the generated output changes and whether the toolbox
+# still passes with it. Only a push to pipeline writes the build to main.
 on:
   push:
     branches:
       - pipeline
     paths-ignore:
       - 'README.md'
+  pull_request:
+    branches:
+      - pipeline
+    paths-ignore:
+      - 'README.md'
   workflow_dispatch:
 
 jobs:
@@ -139,7 +147,10 @@ jobs:
     name: Push updates to main
     runs-on: ubuntu-latest
     needs: [build, test-code]
-    if: needs.test-code.result == 'success' && needs.build.outputs.build_updated == 'true'
+    if: >-
+      github.event_name != 'pull_request' &&
+      needs.test-code.result == 'success' &&
+      needs.build.outputs.build_updated == 'true'
     steps:
       - name: Checkout main branch
         uses: actions/checkout@v6