What should I use to test APIs with OpenAPI files?

If you want to test APIs from an OpenAPI file (.json or .yaml), good options are:

Best general-purpose tools

• Postman
  Import OpenAPI specs, generate collections, run requests, add tests, and use Newman for CI.

• Insomnia
  Great for interactive API testing, supports OpenAPI import, and is simpler than Postman for many people.

• Swagger UI / Swagger Editor
  Best for viewing and trying out endpoints directly from the spec, but less ideal for full test workflows.

For automated API testing

• Newman
  Command-line runner for Postman collections. Good for CI/CD once you’ve built tests in Postman.

• Dredd
  Specifically validates an API implementation against an OpenAPI/Swagger definition.

• Schemathesis
  Very useful for property-based / fuzz-style testing against OpenAPI specs; good for finding edge cases.

• Prism
  Mock server and validator based on OpenAPI; useful for contract testing and development.

For contract/API validation in CI

• Stoplight Prism
• Dredd
• Schemathesis

Quick recommendation

• Manual testing: Postman or Insomnia
• Spec-driven contract testing: Dredd or Prism
• Finding weird edge cases automatically: Schemathesis
• CI execution of Postman tests: Newman

If you tell me whether you want manual testing, automated tests, CI, or contract validation, I can recommend the best one for your setup.