Mock Service Worker vs Prism
Feature checklists rarely decide anything. What decides it is the pricing metric, who has to write the tests, and which limitation you can live with.
Entry price
Free and open source
Open sourceFree and open source
Open sourceWhat drives the bill
The metric that actually scales your invoice.
Free and open source. You pay in engineering time and CI minutes.
Free and open source. You pay in engineering time and CI minutes.
Free tier
Everything, self-hosted
Everything, self-hosted
Open source
MIT
Apache-2.0
Self-hostable
No-code authoring
Languages
Platforms
Fits teams
Adoption
Category standard
OSS community · since 2020
Established
Stoplight (SmartBear) · since 2017
Strengths
- One set of handlers reused across unit, component, E2E and local development.
- Application code is completely unaware it is being mocked — no test-only branches.
- Supports REST and GraphQL with the same model.
- The mock is generated from the spec, so it cannot silently diverge from the contract.
- Validation proxy mode checks that a real implementation matches its own spec.
- Zero configuration beyond having an OpenAPI file.
Limitations
- JavaScript ecosystem only.
- Service Worker registration adds a setup step and occasional caching confusion.
- Handlers can drift from the real API without contract verification.
- Useless without an accurate OpenAPI document.
- Limited stateful behaviour — it is spec-driven, not scenario-driven.
- Generated example data is uninteresting unless examples are in the spec.
Best for
Front-end teams that want one mocking approach across every kind of test.
Design-first API teams who want mocks that are provably in sync with the contract.
Pricing last reviewed August 2026 and is indicative only — confirm on each vendor’s own page.