It's a TypeScript Language Service plugin. Once installed, your IDE will start showing errors based on your new tsconfig settings.

You can suppress these errors using a special comment, @ts-migrating.

It also comes with a CLI. For example, `ts-migrating annotate`, which finds and annotates all current violations. This lets you enable the new tsconfig immediately while preventing new violations from being introduced.

From there, you can fix the suppressed errors over time at your own pace.