GitHub Actions

What is GitHub Actions?

Automation that runs in the cloud, triggered by events in your repository.

• Runs on GitHub's servers

  No local setup needed. Every contributor gets the same environment.

• Triggered by events

  Push a commit, open a pull request, merge to main — Actions reacts automatically.

• The server-side safety net

  Pre-commit hooks can be skipped locally. GitHub Actions can't be bypassed.

• Reusable building blocks

  Use community-built Actions from the GitHub Marketplace — no reinventing the wheel.

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How does it work?

The flow

1. You push code to GitHub
2. GitHub reads your workflow files
3. A runner (a fresh virtual machine) spins up
4. Your steps execute in order
5. All pass → green tick on your PR
6. Any fail → red cross, merge is blocked

The workflow file

One YAML file defines everything:

.github/workflows/tests.yml

name: Run tests

on: [push, pull_request]

jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: astral-sh/setup-uv@v5
      - run: uv run pytest tests/

• Stored in .github/workflows/
• on: controls when it triggers
• steps: are the commands to run

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Pre-commit hooks vs GitHub Actions

• Pre-commit hooks

  Fast, local, immediate feedback. Runs before you can even push.

• GitHub Actions

  Server-side, can't be skipped, runs in a clean environment every time.

Use both

Hooks give you speed. Actions give you the guarantee. Together they cover every angle.