Side by side
Mock Service Worker vs OpenAPI Server
Both stand on api mocking tools. Which one you can start free with, which one lets you read the code, and what each costs once you pay.
Free plan Self-hostedWeb
MSW offers reusable request mocking across browser and Node.js contexts, with support for several API protocols and clients. Its interception approach has browser and Node.js boundaries, so check those limits against the requests your application makes.
Visit Mock Service Worker Free plan APISelf-hosted
OpenAPI Server covers local mocking, specification validation, and optional backend proxying. Its runtime requirement and lack of TypeScript mock support are important considerations.
Visit OpenAPI ServerThe facts
| Mock Service Worker | OpenAPI Server | |
|---|---|---|
| Free plan | Yes | Yes |
| Open source | Not published | Not published |
| Runs on | Self-hosted, Web | API, Self-hosted |
| Lowest paid plan | Not published | Not published |
| Plans published | None | None |
| Maker | Not published | Not published |
| Website | mswjs.io | github.com |
| On api mocking tools | #18 of 26 | #22 of 26 |
Mock Service Worker: what it does well
- Free and open source.
- Mocks HTTP, GraphQL, SSE and WebSocket APIs.
- Mock handlers can be reused across environments.
- Works with native fetch, Axios, React Query and Apollo.
What to know first
- Browser use requires serving a Service Worker script.
- Firefox page XMLHttpRequest requests are not reported to the worker.
- Direct net.connect() and net.createConnection() requests cannot be intercepted.
- Official Egghead courses require a paid subscription.
OpenAPI Server: what it does well
- Validates OpenAPI 3 and Swagger/OpenAPI 2 specifications.
- Supports JSON, JavaScript, and Express middleware mocks.
- Can proxy requests and optionally validate responses.
- Includes HTTP, HTTPS, static files, and watch mode.
What to know first
- Requires Node.js 18 or later.
- TypeScript mock files are not supported.
- JavaScript mocks must run at runtime.
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