Mock Service Worker (MSW)

Mock Service Worker (MSW) revolutionizes API mocking by leveraging service worker technology to intercept network requests seamlessly across browser and Node.js environments, enabling developers to create realistic API mocking that works identically in testing, development, and production debugging scenarios. This innovative platform transforms API mocking from complex server setup and configuration into client-side request interception that feels natural and requires minimal setup while providing comprehensive mocking capabilities.

Trusted by frontend developers, testing teams, and development organizations worldwide seeking realistic API mocking without complex backend setup, MSW excels at service worker-based interception, cross-environment compatibility, and realistic API simulation while maintaining the developer experience that makes comprehensive API mocking practical and maintainable. The platform’s strength lies in its unique approach that makes mocked APIs indistinguishable from real APIs to application code.

Whether you’re a frontend developer building applications with external APIs, a testing engineer creating comprehensive integration tests, a development team requiring offline development capabilities, or anyone needing realistic API mocking without backend complexity, MSW provides the API mocking foundation that transforms complex server mocking into seamless request interception. Its focus on realism, simplicity, and cross-environment compatibility makes it essential for modern development workflows requiring reliable API simulation.

Key Features

• Service worker-based interception - Browser-native request interception that works seamlessly without server setup • Universal API support - Mock REST APIs, GraphQL endpoints, and any HTTP-based service • Cross-environment consistency - Identical behavior in development, testing, and browser debugging environments • Dynamic response generation - Create realistic, stateful API behaviors with conditional logic • Comprehensive network simulation - Test delays, timeouts, errors, and various network conditions • Framework-agnostic design - Works with any JavaScript framework, library, or testing environment • Zero-configuration setup - Minimal setup with intuitive API that requires no complex configuration • TypeScript-first development - Full TypeScript support with excellent type inference and safety

Pros and Cons

Pros

• Service worker approach provides most realistic API mocking available • Works identically across development, testing, and debugging environments • No server setup or backend configuration required • Excellent developer experience with minimal learning curve • Strong TypeScript support and type safety • Active development with regular updates and community support

Cons

• Service worker limitations in some browser environments • Requires modern browser support for service worker technology • Less suitable for complex server-side testing scenarios • Learning curve for developers unfamiliar with service worker concepts • Limited to client-side request interception patterns

Get Started with Mock Service Worker

Ready to implement seamless API mocking with service workers? Visit MSW to create realistic API simulations that work across all development environments.

How It Compares

Mock Service Worker differentiates itself from competitors like WireMock and nock through its innovative service worker approach that provides the most realistic API mocking without requiring server infrastructure or complex setup procedures. While WireMock offers more server-side features and Mirage JS provides more comprehensive application mocking, MSW delivers the most seamless and realistic API interception that works identically across all JavaScript environments. Unlike traditional mocking libraries that require application code changes or server setup, MSW’s strength lies in its transparent request interception that makes mocked APIs indistinguishable from real ones. For developers seeking realistic, maintainable API mocking without infrastructure complexity, MSW provides the most innovative and practical solution available.

Get Started with MSW

Mock APIs seamlessly with service workers. Visit mswjs.io to implement realistic API mocking.