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@mswjs

Mock Service Worker

Industry standard API mocking for JavaScript.

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Mock Service Worker is an API mocking library for browser and Node.js that uses a Service Worker to intercept requests that actually happened. This means no request client stubs and unmatched resilience when it comes to request integrity, as your app now performs requests the same way it does in production.

Ecosystem

We favor composition in both how we write our code and how we distribute it. That's why instead of building a single monolithic package that's responsible for too many things, we distribute the core module with the essentials that everybody could use, and provide a set of standalone extensions that enable specific workflows and push the developer experience even further.

Native extensions

Package Description
@mswjs/data Model and query your mock data (fixtures).
@mswjs/source Generate request handlers from various sources (HAR files, OpenAPI documents).
@mswjs/http-middleware Spawn an HTTP server from your request handlers.

Third-party extensions

Package Description
@msw/playwright Official Playwright integration.
msw-storybook-addon Official Storybook add-on.

Support us!

This project is the result of hundreds of hours of work that our contributors spend so that you could enjoy the best API mocking experience there is to offer. If you'd like us to bring new features and mitigate issues more effectively, consider supporting us.

👉 Support Mock Service Worker via GitHub Sponsors

By becoming a baker you help us ensure a bright future for the project. We value and treasure every contribution, big or small. Thank you.

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  1. msw msw Public

    Industry standard API mocking for JavaScript.

    TypeScript 16.9k 553

  2. examples examples Public

    Examples of Mock Service Worker usage with various frameworks and libraries.

    703 211

  3. data data Public

    Data modeling and relation library for testing JavaScript applications.

    TypeScript 886 57

  4. interceptors interceptors Public

    Low-level network interception library.

    TypeScript 611 141

  5. msw-storybook-addon msw-storybook-addon Public

    Mock API requests in Storybook with Mock Service Worker.

    TypeScript 459 42

  6. http-middleware http-middleware Public

    Spawn an HTTP server from your request handlers or apply them to an existing server using a middleware.

    TypeScript 120 14

Repositories

Showing 10 of 23 repositories
  • msw Public

    Industry standard API mocking for JavaScript.

    mswjs/msw’s past year of commit activity
    TypeScript 16,853 MIT 553 47 (6 issues need help) 13 Updated Jun 20, 2025
  • mswjs.io Public

    Official website and documentation for the Mock Service Worker library.

    mswjs/mswjs.io’s past year of commit activity
    TypeScript 168 195 9 (1 issue needs help) 14 Updated Jun 14, 2025
  • playwright Public

    Mock Service Worker binding for Playwright.

    mswjs/playwright’s past year of commit activity
    TypeScript 138 MIT 2 1 0 Updated Jun 14, 2025
  • socket.io-binding Public

    Binding to mock Socket.IO connections with Mock Service Worker.

    mswjs/socket.io-binding’s past year of commit activity
    TypeScript 9 3 2 0 Updated Jun 13, 2025
  • interceptors Public

    Low-level network interception library.

    mswjs/interceptors’s past year of commit activity
    TypeScript 611 MIT 141 24 (1 issue needs help) 16 Updated Jun 11, 2025
  • source Public

    Generate MSW request handlers from various sources (HAR files, OpenAPI documents, etc).

    mswjs/source’s past year of commit activity
    TypeScript 170 MIT 8 10 1 Updated Jun 11, 2025
  • http-middleware Public

    Spawn an HTTP server from your request handlers or apply them to an existing server using a middleware.

    mswjs/http-middleware’s past year of commit activity
    TypeScript 120 14 4 (1 issue needs help) 1 Updated Jun 11, 2025
  • msw-storybook-addon Public

    Mock API requests in Storybook with Mock Service Worker.

    mswjs/msw-storybook-addon’s past year of commit activity
    TypeScript 459 MIT 42 15 (1 issue needs help) 2 Updated Jun 5, 2025
  • .github Public

    Mock Service Worker organization GitHub files.

    mswjs/.github’s past year of commit activity
    0 0 0 0 Updated Jun 5, 2025
  • data Public

    Data modeling and relation library for testing JavaScript applications.

    mswjs/data’s past year of commit activity
    TypeScript 886 MIT 57 49 (5 issues need help) 12 Updated May 29, 2025

Sponsors

  • @sentdm
  • @k-paxian
  • @stackblitz
  • @getsentry
  • @syntaxfm
  • @ryanmagoon
  • @niccholaspage
  • @laststance
  • @KhaledMohamedP
  • @andris-silis
  • @vital-software
  • @chromaui
  • @erikras

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