Open-source ReadyAPI alternatives

Karate is an open-source tool that unifies API testing, mocks, performance testing and UI automation in one framework with a single readable syntax. Tests are written as feature files, so people who are not Java developers can read and write them, and the project is written in Java.

Its documentation highlights the match keyword for validating complete responses, headers and arrays, parallel execution of features, scenarios and example rows, reusable flows by calling one feature from another, and test doubles that stand up HTTP, gRPC and message-queue mocks from a feature file. Karate v2 adds virtual threads, a single-binary CLI, JavaScript debugging and soft assertions. There are extensions for VS Code and IntelliJ, plus Karate Agent and Karate Xplorer products.

Tests can be run through JUnit, the command line or CI/CD pipelines. Karate is licensed under MIT, and topics mention BDD, Cucumber, contract testing, load testing and WebDriver. It suits QA engineers and developers who want one tool for API-level and UI-level checks.

Mockoon is an open-source tool for designing and running mock APIs. It combines a desktop application for building mock servers locally with a command-line tool for running those mocks in headless environments, and it requires no remote deployment or account.

API mocking reduces dependence on external services and their limits such as rate limits, costs and availability. Mockoon lets you control routes in detail, including HTTP methods and statuses, regex paths, file serving and custom headers. It supports OpenAPI import, JSON templating, HTTPS, a proxy forwarding mode and logs of incoming and forwarded requests. Teams can simulate errors and latencies and onboard new members with a consistent test environment.

The desktop app is built with Electron and TypeScript under the MIT licence and installs through Homebrew, winget, Chocolatey, the Windows Store, Snap or AUR. The CLI is also available as a Docker image for self-hosting mock APIs, and a separate cloud offering supports team collaboration, data sync and deployment of mock APIs.

Zerocode, also called zerocode-tdd, is a community-developed open-source testing framework for REST and SOAP APIs, microservices, Kafka data streams, databases and ETL or data pipelines. Test scenarios are written in JSON or YAML, so testers can create and maintain automated checks with very little code.

The framework handles response validation, invoking target APIs, load and stress testing and security testing through straightforward steps. A command-line companion called Steply lets you run tests directly from a terminal, and Zerocode is also available as a Maven dependency for Java projects. Documentation is indexed and searchable, and a Slack channel and mailing list support users. The README gives an example of validating a REST GET request against an expected payload and status code.

Zerocode is written in Java and licensed under Apache-2.0, and runs in your own build or CI environment. It suits developers and QA engineers who want declarative API and Kafka tests that non-programmers can read and maintain.

Step CI is an API quality assurance framework aimed at developers who need to test several different API styles within the same test workflow, rather than using separate tools for REST, GraphQL and other protocols. It is language-agnostic, letting workflows be configured in YAML, JSON or JavaScript.

It supports testing REST, GraphQL, gRPC, tRPC and SOAP APIs, can run self-hosted on a local network, locally, or inside a CI/CD pipeline, and integrates with other tooling such as GitHub Actions. The README specifically calls out migration guidance for users coming from Postman and Insomnia, and an online playground is available to try workflows without installing anything.

The CLI can be installed via Node.js or Homebrew, and by default collects anonymous usage data, including a unique user ID, OS name, Node version and which commands are run, which can be disabled with an environment variable. Step CI is written in TypeScript and released under the Mozilla Public License 2.0, with a separate paid support plan offering SLA-backed support, onboarding and prioritized feature requests on top of the free core.