Prism 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
Apache-2.0
MIT
Self-hostable
No-code authoring
Languages
Platforms
Fits teams
Adoption
Established
Stoplight (SmartBear) · since 2017
Emerging
Nucleus Cloud (acquired by Grow Therapy) · since 2023
Strengths
- 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.
- 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
- 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.
- 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
Design-first API teams who want mocks that are provably in sync with the contract.
Realistically, nobody starting fresh. Existing self-hosted users can keep running it, but plan a migration to Tonic or a maintained alternative.
All of these integrate with: GitHub Actions.
Pricing last reviewed August 2026 and is indicative only — confirm on each vendor’s own page.