diff --git a/.github/workflows/pydoctor_primer.yaml b/.github/workflows/pydoctor_primer.yaml
new file mode 100644
index 000000000..3fa8d416d
--- /dev/null
+++ b/.github/workflows/pydoctor_primer.yaml
@@ -0,0 +1,117 @@
+name: Run pydoctor_primer
+
+on:
+  # Only run on PR, since we diff against master
+  pull_request:
+    paths-ignore:
+    - 'pydoctor/test/**'
+    - 'docs/**'
+    - '*.rst'
+    - '*.txt'
+    - '*.in'
+    - '*.md'
+    - '.*'
+    - 'setup.py'
+
+
+jobs:
+  pydoctor_primer:
+    name: Run pydoctor_primer
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      pull-requests: write
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          path: pydoctor_to_test
+          fetch-depth: 0
+      - uses: actions/setup-python@v4
+        with:
+          python-version: "3.11"
+      - name: Install pydoctor_primer
+        run: |
+          python -m pip install -U pip
+          pip install git+https://github.com/twisted/pydoctor_primer.git
+      - name: Run pydoctor_primer
+        shell: bash
+        run: |
+          cd pydoctor_to_test
+          echo "new commit"
+          git rev-list --format=%s --max-count=1 $GITHUB_SHA
+
+          MERGE_BASE=$(git merge-base $GITHUB_SHA origin/$GITHUB_BASE_REF)
+          git checkout -b base_commit $MERGE_BASE
+          echo "base commit"
+          git rev-list --format=%s --max-count=1 base_commit
+
+          echo ''
+          cd ..
+          # fail action if exit code isn't zero or one
+          (
+            pydoctor_primer \
+            --repo pydoctor_to_test \
+            --new $GITHUB_SHA --old base_commit \
+            --debug \
+            --output concise \
+            -j 8 \
+            | tee diff.txt
+          ) || [ $? -eq 1 ]
+
+      - name: Post comment
+        id: post-comment
+        uses: actions/github-script@v6
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+          script: |
+            const MAX_CHARACTERS = 30000
+            const MAX_CHARACTERS_PER_PROJECT = MAX_CHARACTERS / 3
+
+            const fs = require('fs')
+            let data = fs.readFileSync('diff.txt', { encoding: 'utf8' })
+
+            function truncateIfNeeded(original, maxLength) {
+              if (original.length <= maxLength) {
+                return original
+              }
+              let truncated = original.substring(0, maxLength)
+              // further, remove last line that might be truncated
+              truncated = truncated.substring(0, truncated.lastIndexOf('\n'))
+              let lines_truncated = original.split('\n').length - truncated.split('\n').length
+              return `${truncated}\n\n... (truncated ${lines_truncated} lines) ...`
+            }
+
+            const projects = data.split('\n\n')
+            // don't let one project dominate
+            data = projects.map(project => truncateIfNeeded(project, MAX_CHARACTERS_PER_PROJECT)).join('\n\n')
+            // posting comment fails if too long, so truncate
+            data = truncateIfNeeded(data, MAX_CHARACTERS)
+
+            console.log("Diff from pydoctor_primer:")
+            console.log(data)
+
+            let body
+            if (data.trim()) {
+              body = 'Diff from [pydoctor_primer](https://github.com/tristanlatr/pydoctor_primer), showing the effect of this PR on open source code:\n```diff\n' + data + '```'
+            } else {
+              body = "According to [pydoctor_primer](https://github.com/tristanlatr/pydoctor_primer), this change doesn't affect pydoctor warnings on a corpus of open source code. ✅"
+            }
+            const ev = JSON.parse(
+              fs.readFileSync(process.env.GITHUB_EVENT_PATH, 'utf8')
+            )
+            const prNumber = ev.pull_request.number
+
+            await github.rest.issues.createComment({
+              issue_number: prNumber,
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              body
+            })
+            return prNumber
+
+      - name: Hide old comments
+        uses: kanga333/comment-hider@v0.4.0
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          leave_visible: 1
+          issue_number: ${{ steps.post-comment.outputs.result }}
\ No newline at end of file