Mock Service Worker vs Neosync
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.
The MIT-licensed code remains free to self-host. The paid cloud service no longer exists — neosync.dev is offline.
Free tier
Everything, self-hosted
Everything, self-hosted
Open source
MIT
MIT
Self-hostable
No-code authoring
Languages
Platforms
Fits teams
Adoption
Category standard
OSS community · since 2020
Emerging
Nucleus Cloud (acquired by Grow Therapy) · since 2023
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.
- Open source and self-hostable, so sensitive data never leaves your infrastructure.
- Preserves referential integrity across tables.
- The last release is feature-complete for common Postgres and MySQL anonymisation work.
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.
- Archived and unmaintained since August 2025 — no security patches, no new connectors, no support.
- The hosted cloud has been shut down, so self-hosting is the only option.
- Fewer database connectors than the incumbents.
Best for
Front-end teams that want one mocking approach across every kind of test.
Realistically, nobody starting fresh. Existing self-hosted users can keep running it, but plan a migration to Tonic or a maintained alternative.
Pricing last reviewed August 2026 and is indicative only — confirm on each vendor’s own page.