REST Assured

What it is

REST Assured is an open source Java library that makes testing and validating REST services in Java almost as concise as in dynamic languages. You describe the request with given(), send it with when(), and assert on the response with then(), including status codes, headers and JSON or XML body fields using path expressions. It is licensed under Apache 2.0.

What it is used for

• Functional API tests in Java projects, run by JUnit 5 or TestNG in the same build as other tests.
• Checking status codes, headers, response times and body values with readable matchers.
• Authentication flows, request and response logging, and reusable request and response specifications.
• JSON Schema validation through a companion module.

As of 2026-09, the official site lists version 6.0.1, released on 10 July 2026, with support for Spring 7 and Jackson 3.

Is it worth your time?

If you work, or want to work, in a Java team, yes: many API test suites in enterprises and service companies are written with REST Assured, often alongside Selenium. If you test APIs in JavaScript, learn to read it rather than write it; the concepts map directly to Playwright's request fixture or other code-based tools.

Prerequisites

Basic Java, a build tool such as Maven or Gradle, a test framework such as JUnit 5 or TestNG, and a solid understanding of HTTP, status codes and JSON.

Free or paid?

Free and open source.

What you can do after

Write maintainable API test suites in Java with shared specifications for base URLs and authentication, data-driven cases through your test framework, and schema checks, all runnable in CI with the rest of the build.

How to learn it

Start with the official usage guide on GitHub, then write tests against a practice API such as Restful-booker. Test Automation University also has a free course on automating API tests with REST Assured.

Common questions

REST Assured or Postman? Postman is excellent for exploring and quick checks; REST Assured suits large, code-reviewed suites in Java projects. Many teams use both.

Does it work with Kotlin? Yes, there are Kotlin extensions, but most examples you will find use Java.