Prism vs LocalStack

Free and open source

From $35 per user/month (indicative, Pro)

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

Community edition is genuinely useful; Pro adds services such as RDS, ECS and advanced IAM enforcement.

Everything, self-hosted

Community edition covers the most-used AWS services and is free.

Established

Stoplight (SmartBear) · since 2017

Category standard

LocalStack · since 2017

• 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.

• Integration tests against AWS services run offline in seconds at no cloud cost.
• Removes the shared-sandbox-account contention that plagues cloud teams.
• Works with Terraform and CDK, so infrastructure code is testable.

• 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.

• Emulation is not identical to AWS; some behaviours and IAM semantics differ.
• Many services are Pro-only.
• Keeping up with AWS feature changes means occasional gaps.

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

AWS-native teams whose tests currently depend on a shared cloud account.