The **check‑yarn‑lock** tool is a tiny command‑line program intended to run as a Git pre‑commit hook in Yarn‑based JavaScript projects. It scans staged changes and aborts the commit with an error if any `package.json` dependency is modified without a corresponding update to `yarn.lock`, helping developers keep their lockfile in sync with dependency changes. Suitable for any team using Yarn who want to enforce this best‑practice automatically.