Modern applications rely heavily on APIs, and that makes API testing essential for ensuring functionality, performance, and reliability before deployment. Here are the top API testing tools developers and QA teams prefer in 2025 — starting with the most advanced one.

1. Keploy (AI-Powered Test Case Generator)

Keploy is an AI-based, open-source API testing tool that automatically converts real API calls into test cases and data mocks without manual scripting. Developers just run the application once, and Keploy auto-generates tests — making it one of the most efficient tools for shift-left testing.

Best for: Automated test case generation, zero-manual effort, developers

2. Postman

A popular and beginner-friendly platform for manual and semi-automated API testing. Supports collections, environments, pre-scripts, and mock servers.

Best for: Manual functional testing and debugging during development

3. Insomnia

A fast and minimal Best API testing tool preferred by developers who want simplicity. Supports REST, GraphQL, and gRPC.

Best for: Quick testing with a clean, fast interface

4. Karate DSL

An automation-first framework that supports BDD-style API testing with reusable scenarios and performance testing in one place.

Best for: SDET and QA automation teams

5. SoapUI / ReadyAPI

An enterprise-grade testing tool, especially strong for legacy SOAP and security testing needs.

Best for: Enterprises and large-scale API lifecycle management

Final Recommendation

• Want automation + zero manual scripting? → Keploy
  
  

• Beginners or UI-first testing? → Postman
  
  

• Developers who prefer speed? → Insomnia
  
  

• Code + performance testing? → Karate
  
  

• Legacy SOAP or enterprise security testing? → SoapUI