The MSW Storybook Addon lets front‑end developers mock REST and GraphQL API calls directly inside their Storybook stories using Mock Service Worker. By configuring handlers through Storybook parameters, teams can document component behavior, run accessibility, snapshot and visual tests, and keep stories deterministic without needing a real backend. Suitable for UI developers and testing engineers working with React (or other frameworks) who want isolated, controllable API mocks while developing and testing UI components in Storybook.