Speed up GitHub Actions with dependency caching

Cache node_modules, pip wheels, and Go modules keyed on your lockfile hash, and warm the cache on main to cut minutes off every GitHub Actions run.

If every GitHub Actions run reinstalls dependencies from scratch, you are paying for the same download on every push. The actions/cache action stores a directory keyed on your lockfile and restores it next run — a one-line change that often halves wall-clock time.

Key the cache on your lockfile

The key decides when the cache is reused. Hash the lockfile so it invalidates the moment dependencies change, and add a restore-keys fallback so a near-miss still restores most of it.

- uses: actions/cache@v4
  with:
    path: ~/.npm
    key: npm-${{ runner.os }}-${{ hashFiles('package-lock.json') }}
    restore-keys: |
      npm-${{ runner.os }}-

The setup actions already do this

For common languages you do not even need the cache action — the setup-* actions have it built in.

- uses: actions/setup-node@v4
  with:
    node-version: 20
    cache: npm        # restores + saves ~/.npm automatically

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