Mock Service Worker 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.

Category standard

OSS community · since 2020

Category standard

LocalStack · since 2017

• 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.

• 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.

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

• 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.

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

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