Mock Service Worker vs Neosync

Free and open source

From $20 per user/month (indicative, cloud)

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

Self-hosting is free; the cloud service is priced per user and record volume.

Everything, self-hosted

Open-source self-hosted edition is free.

Category standard

OSS community · since 2020

Emerging

Nucleus Cloud · since 2023

• 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.

• Open source and self-hostable, so sensitive data never leaves your infrastructure.
• Preserves referential integrity across tables.
• Far cheaper than the commercial data-privacy platforms.

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

• Young project with a small community.
• Fewer database connectors than the incumbents.
• Self-hosting is operational work.

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

Teams that need anonymised test data but cannot justify enterprise pricing.