Prism 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.

Established

Stoplight (SmartBear) · since 2017

Emerging

Nucleus Cloud · since 2023

• 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.
• Far cheaper than the commercial data-privacy platforms.

• 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.

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

Design-first API teams who want mocks that are provably in sync with the contract.

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