Mock Service Worker (MSW)
A reusable API mocking library that intercepts network requests for testing and development across JavaScript environments
- Also known as
- mock-service-worker-msw
Available worldwide
What is Mock Service Worker (MSW)?
An open-source API mocking library that uses the Service Worker API to intercept network requests in browsers and Node.js, enabling developers to mock REST, GraphQL, and WebSocket APIs for testing and development without modifying application code.
Mock Service Worker (MSW) pricing
We don't have Mock Service Worker (MSW)'s full plan breakdown yet (its pricing page resisted automated reading). Here's what we could confirm. Always check live pricing for exact numbers.
Free and open source
What Mock Service Worker (MSW) does
The capabilities that matter for api mocking, normalised so it lines up with every alternative. “-” means we haven't confirmed it, not that it's missing.
- Mocking mode
- Dynamic templating
- Stateful scenarios
- ✓
- Fault chaos injection
- -
- Openapi import
- ✓
- Proxy passthrough
- -
- Admin API
- -
- Deployment
- Embedded library
- Legacy protocol virtualization
- -
- Collaboration sharing
- -
- Ci cd integration
- ✓
- Open source
- ✓
- Market segment
- Dev tool
- Pricing model
- Open source
Platform & deployment
Independently observed- CLI
- Web
Integrations (10)
Independently observed- Vitest
- Playwright
- Storybook
- React Native
- Express
- fetch
- axios
- react-query
- Hono•
- Fastify•
Security & compliance
Known vulnerabilities: 0 (0 in the last 12 months) sourcea count reflects scale & disclosure, not quality
Mock Service Worker (MSW) FAQ
Common questions about Mock Service Worker (MSW), answered from independent, dated evidence.
What is Mock Service Worker (MSW)?
An API mocking library that intercepts network requests at the browser and Node.js levels, allowing consistent mock responses across testing frameworks, tools, and applications without requiring client-specific stubs or configuration. It is indexed under API Mocking.
Source: https://mswjs.io
Is Mock Service Worker (MSW) free to use?
Mock Service Worker (MSW) is open source, so it can be self-hosted and used at no licence cost. It is released under the MIT licence. Pricing changes often, so verify at source before relying on it.
Source: https://mswjs.io
What platforms does Mock Service Worker (MSW) support?
Mock Service Worker (MSW) supports the web and a command-line interface. Platforms we have not confirmed are simply not listed here rather than ruled out.
Source: https://mswjs.io
What does Mock Service Worker (MSW) integrate with?
We have confirmed 8 integrations for Mock Service Worker (MSW), including Vitest, Playwright, Storybook, React Native, Express, fetch, axios and react-query. This is what we could verify from public sources, so the vendor may support others we have not indexed.
Source: https://mswjs.io
Is Mock Service Worker (MSW) open source?
Yes. Mock Service Worker (MSW) is published under the MIT licence, a permissive licence that generally allows commercial use and modification. Licence terms can change between releases, so verify against the repository for the version you intend to use.
Source: https://github.com/mswjs/msw
Mock Service Worker (MSW) alternatives
Other api mocking we track, ranked by the same independent score.
- BeeceptorCreate and manage mock API servers for testing and developmentmedium · 74%
- Mockoonmedium · 72%
- json-serverRapidly create a mock REST API from JSON data for development and testingmedium · 64%
- NockA Node.js library for mocking HTTP interactions in testsmedium · 67%
- WireMockAn open source tool for creating and testing mock APIslow · 17%
- Traffic ParrotEnables teams to mock external APIs and services locally during development and testingmedium · 72%
Compare Mock Service Worker (MSW)
Side by side against other api mocking, attribute by attribute, with a source on every value.
The vioscaleAI score: one lens on the evidence
Not user reviews and not a paid placement: a confidence-weighted blend of the independent signals below (adoption, activity, security posture, and more), which you can sort and re-weight yourself. Vendors can correct their listing but can never move their rank, and stars are weighted low as a vanity metric. It is one way to read the evidence for Mock Service Worker (MSW), not the verdict.
| Signal | Score | Weight | Contribution | Evidence |
|---|---|---|---|---|
| Release cadence | 99 | 0.07 | 6.6 | ✓ |
| Capabilities | 67 | 0.08 | 5.6 | ✓ |
| Dependent projects | 68 | 0.08 | 5.4 | ✓ |
| Development activity | 38 | 0.12 | 4.5 | ✓ |
| Security score | 62 | 0.05 | 3.3 | ✓ |
| Stars | 80 | 0.03 | 2.7 | ✓ |
| Integrations | 27 | 0.05 | 1.5 | ✓ |
| Security posture | 0 | 0.09 | 0.0 | - |
| Package downloads | 0 | 0.17 | 0.0 | - |
| Developer Q&A activity | 0 | 0.08 | 0.0 | - |
Computed . Re-weight it by intent, or see the full method.
All data & sourcesshow ↓
Every value we hold, with its source, retrieval date, and confidence. This is the evidence behind the score: don't trust it, verify it.
Activity
| Attribute | Value | Evidence |
|---|---|---|
| Commits last 30d | 15 | mediumsource · 2026-10-14 · 65% |
Adoption
Content
| Attribute | Value | Evidence |
|---|---|---|
| Faq | 5 items | mediumsource · 2026-09-10 · 67% |
Features
| Attribute | Value | Evidence |
|---|---|---|
| Capabilities | Deployment: embedded_library · Open source: Yes · Mocking mode: dynamic_templating · Pricing model: open_source · Market segment: dev-tool · Openapi import: Yes | mediumsource · 2026-10-14 · 60% |
Integrations
| Attribute | Value | Evidence |
|---|---|---|
| Count | 8 | mediumsource · 2026-08-17 · 60% |
Language
| Attribute | Value | Evidence |
|---|---|---|
| Primary | TypeScript | highsource · 2026-10-14 · 90% |
License
| Attribute | Value | Evidence |
|---|---|---|
| Spdx | MIT | highsource · 2026-10-14 · 95% |
Market
| Attribute | Value | Evidence |
|---|---|---|
| Availability | PrimaryMarkets: … · AvailabilityScope: global · AvailableCountries: … · NotAvailableCountries: … | highsource · 2026-10-14 · 75% |
Pricing
Release
Security
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