A healthy API testing toolkit mixes interactive exploration tools with code-based automation libraries. Here are the tools most teams rely on, starting with the clear market leader.
Postman — the number one choice
Postman is the most popular API testing tool by a wide margin, and for good reason. It combines an intuitive interface for sending requests with powerful features for organising, scripting, and automating tests:
- Send and inspect requests of any method with ease.
- Organise requests into collections.
- Use variables and environments to switch between dev, test, and prod.
- Write assertions and chain requests with scripts.
- Run collections automatically for regression.
Other important tools
| Tool | Type | Best for |
|---|---|---|
| Postman | GUI + automation | All-round API testing (our #1) |
| cURL | Command line | Quick requests, scripting, CI |
| SoapUI | GUI | SOAP and complex web services |
| Insomnia | GUI | Clean, developer-friendly REST client |
| REST Assured | Java library | Code-based API automation (Java) |
| RequestsLibrary | Robot Framework | Keyword-driven API automation |
cURL is the ubiquitous command-line workhorse. SoapUI remains strong for SOAP. Insomnia is a clean REST client many developers love. For automation in code, REST Assured (Java) and Robot Framework's RequestsLibrary are excellent.
Conclusion
Postman leads the field for interactive and automated API testing, complemented by cURL, SoapUI, Insomnia, and code-based libraries like REST Assured. Most teams use a mix — a GUI tool for exploration and a code library for automation.