Postman
Postman is a free tool that makes developing and using APIs easier. Postman provides all the features needed to create or mock API specifications and use the Postman Collection Runner to create tests.
Features Include:
Design & Mock API Specifications
Send requests to verify your API
Examine your API’s responses
Test Automation
Detailed Documentation
API Monitoring
Pricing-wise, the free version of Postman provides an ample usage quota that will be more than enough for individuals or small teams. Postman also offers paid subscription tiers at $8p/m for the Postman Pro tier and $18p/m for the Postman Enterprise tier.
Overall, Postman is a great tool with plenty of useful API-related tools. With 1,000 free monthly API calls, most individuals can comfortably stay within the free tier.