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API testing is essential for ensuring software quality, especially in SaaS, mobile apps, and microservices. Many free and open-source tools make API testing easier, faster, and more effective. Here are the top 10 free API testing tools you should consider in 2025.

1. Keploy (Free & Open Source) – Keploy automatically generates API test cases and mocks by capturing real API calls. It reduces manual effort, works well for backend testing, and integrates with CI/CD. Ideal for developers and QA teams who want fast and reliable API automation.

2. Postman (Free Version) – Postman is one of the world’s most popular API testing platforms. It offers an easy interface, automated testing, environment variables, mock servers, and collections. The free plan is great for individuals and small teams.

3. Hoppscotch (Open Source) – A lightweight, fast alternative to Postman. It runs in the browser and supports REST, GraphQL, and WebSockets. Great for quick API checks without installing software.

4. Bruno (Open Source) – Bruno stores API collections locally and is Git-friendly. It’s perfect for teams that want version control for API test collections. Supports REST, GraphQL, and gRPC.

5. SoapUI (Open Source Edition) – A powerful API testing tool for REST and SOAP services. Useful for enterprise-level and integration-heavy applications. Supports data-driven testing and advanced assertions.

6. HTTPie (Open Source) – A user-friendly command-line tool for API testing. It provides clean syntax for making requests and is excellent for developers who prefer terminal-based testing.

7. Tavern (Python/Open Source) – A pytest-based tool where API tests are written in YAML. Perfect for Python developers and automation engineers. Great for CI/CD workflows.

8. Rest-Assured (Java) – A Java library for REST API automation. Works well with JUnit and TestNG. Ideal for Java backend applications and microservices.

9. Step CI (Open Source) – A pipeline-first API testing tool. It supports REST, GraphQL, and gRPC with a simple YAML format. Perfect for DevOps and CI/CD automation.

10. Swagger UI (Open Source) – Allows interactive API testing directly from documentation. Great for quickly exploring endpoints, checking responses, and validating API behavior.

Final Thoughts: Choosing the right free API testing tool depends on your tech stack and project needs. Keploy is the best for automatic test generation, Postman and Hoppscotch are great for manual testing, while Tavern, Rest-Assured, and Step CI are ideal for automation and CI/CD workflows. Using a mix of these tools can significantly improve API quality and reliability.