Karate is an open-source, MIT-licensed Java framework that combines API testing, mocks, performance testing and UI automation into a single unified tool, aimed at teams that need to test APIs and services without stitching several separate tools together.

What it is

Karate lives in the Java and JVM ecosystem and is distributed through Maven Central under the io.karatelabs group, with karate-core as the central artifact. Its stated purpose is to fold four disciplines — API testing, mock servers, performance testing and UI automation — into one framework, so those concerns share a single syntax and a single project rather than four independent toolchains. Project documentation lives at docs.karatelabs.io, and the repository is maintained under the MIT licence.

The concrete problem it addresses is fragmentation. A typical API test effort otherwise needs an assertion library, a BDD or Cucumber-style scenario runner, a standalone mock server for dependencies that are not ready, a load-testing tool for the same endpoints, and a browser automation layer for the UI paths. Karate replaces those separate pieces with one framework, which means one dependency, one test style and one place to maintain assertions and contracts across API, mock, performance and UI layers.

Key capabilities

• API testing with built-in assertions, covering the api-testing and assertions topics.
• BDD and Cucumber-style scenario syntax, listed under the bdd and cucumber topics.
• A built-in mock server for standing in for services that are unavailable or under construction, per the mock-server topic.
• Load and performance testing, listed under load-testing and named in the README as part of the unified framework.
• UI automation, named in the README alongside the API and performance capabilities.
• Contract testing for microservices, covered by the contract-testing and microservices topics.
• Distribution as io.karatelabs:karate-core on Maven Central, with release artifacts published through GitHub Releases and versioned v2 notes kept in README_V2.md.

Who uses it and how

• Microservices teams that need API tests and contract tests across service boundaries in one suite, rather than separate API and contract tooling.
• Teams that stand up the built-in mock server so front-end or downstream work can proceed while a dependency is still being built.
• Performance engineers who reuse the same API scenarios for load testing instead of rewriting them in a second tool.
• Quality engineers covering both API and UI paths who want one framework and one syntax across the two.
• Java and Maven projects, where the dependency resolves from Maven Central; the repository's own pipeline runs through the GitHub Actions workflow referenced by the build badge.

Getting started

Add the io.karatelabs:karate-core dependency from Maven Central to a Java project, then follow the documentation at docs.karatelabs.io. The earlier monolithic README is preserved at the v1.5.2.RC2 tag, whose anchor links still resolve to specific sections.

How it compares

No list of paid products being replaced is provided in the facts, so no licence-and-cost contrast can be drawn. Among similar tools, the facts name Cucumber through the topic list; Karate is positioned by its own README as broader in scope than a BDD runner alone, since API testing, mocking, performance testing and UI automation all sit in the same framework.

When to use it — and when not to

Pick Karate when the team is already on the JVM and wants one framework for API, mock, performance and UI work rather than four tools. A self-hoster must supply a Java and Maven toolchain, since no Docker image or hosted option appears in the facts. Note two caveats: v2 is still in development according to README_V2.md, so version and migration choices need care, and the provided README excerpt is sparse, meaning readers should treat docs.karatelabs.io as the authoritative source.