# Composite Actions — GitHub Actions

Source: https://www.skillbyai.com/en/github-actions/r-composite

> Bundle steps into one action.

## action.yml with runs.using: composite

A **composite action** packages several steps into one reusable step, defined in an `action.yml` with inputs, outputs and `runs: using: composite`. Use it for repeated step sequences (set up toolchain, restore cache, install), while reusable workflows suit whole jobs. Composite actions can live in the same repository (`uses: ./.github/actions/setup`) or their own repository. JavaScript and Docker actions are alternatives when you need more logic.

## A local composite action

Not linted or run here; check the GitHub Actions documentation for current syntax.

```yaml
# .github/actions/setup/action.yml
name: Setup project
inputs:
  node-version:
    default: "22"
runs:
  using: composite
  steps:
    - uses: actions/setup-node@v4
      with: { node-version: "${{ inputs.node-version }}", cache: npm }
    - run: npm ci
      shell: bash        # composite run steps must declare a shell

# usage in a workflow, after actions/checkout:
#   - uses: ./.github/actions/setup
```

## Declare shell in composite run steps

Composite run steps require an explicit shell, a frequent first-time error.

**Quiz:** When is a composite action a better fit than a reusable workflow?

- [ ] When reusing whole multi-job pipelines
- [x] When reusing a sequence of steps inside jobs
- [ ] When you need a cron schedule
- [ ] Never

*Answer:* When reusing a sequence of steps inside jobs. Steps versus jobs.