Mock Service Worker vs Snaplet Seed

Free and open source

Free and open source

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

The Seed library is open source and free; note that Snaplet wound down its hosted product, so treat this as a library rather than a service.

Everything, self-hosted

Everything, self-hosted

Category standard

OSS community · since 2020

Emerging

Snaplet · since 2021

• 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.

• Schema-aware generation means the data actually inserts and the app actually works.
• Deterministic seeds make failing tests reproducible.
• Good TypeScript ergonomics with Prisma and Drizzle.

• JavaScript ecosystem only.
• Service Worker registration adds a setup step and occasional caching confusion.
• Handlers can drift from the real API without contract verification.

• The company wound down its hosted business — evaluate the library's maintenance status before depending on it.
• PostgreSQL-centric.
• TypeScript ecosystem only.

Front-end teams that want one mocking approach across every kind of test.

TypeScript teams that want each developer and CI run to start from a clean, coherent database.