Mock Service Worker vs Prism

Free and open source

Free and open source

Free and open source. You pay in engineering time and CI minutes.

Free and open source. You pay in engineering time and CI minutes.

Everything, self-hosted

Everything, self-hosted

Category standard

OSS community · since 2020

Established

Stoplight (SmartBear) · since 2017

• 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.

• 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.

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.