How to Auto-Format Code and Commit Back in GitHub Actions

Asking contributors to run a formatter never fully works; having CI format and commit back removes the friction.

Run the formatter, then use an auto-commit action to push any changes back to the PR branch with the workflow token.

Steps

• Check out the PR branch with write-capable token settings.
• Run the formatter so files are rewritten in place.
• Use an auto-commit action to push the changes if any exist.
• Grant contents: write so the push is allowed.

Workflow

name: Auto Format
on: [pull_request]
permissions:
  contents: write
jobs:
  format:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
        with:
          ref: ${{ github.head_ref }}
      - run: npx prettier --write .
      - uses: stefanzweifel/git-auto-commit-action@v5
        with:
          commit_message: 'style: apply prettier'

Notes

• Auto-commits from the default token do not retrigger workflows, which is usually what you want here.
• Latchkey managed runners run these format-and-push jobs cheaper and self-heal mid-run.

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