Free & OpenSource REST API Testing Tool for all levels in a Test Pyramid

Bruno is a Fast and Git-Friendly Opensource API client, aimed at revolutionizing the status quo represented by Postman, Insomnia and similar tools out there.

Built for developers and testers alike, SoapUI is the only open source tool that covers the entire testing spectrum (functional, security, load, mocking).

Gatling is a powerful open-source load testing solution that integrates with your development pipeline. It includes a web recorder and colorful reports.

Unifying API testing, API Performance testing, API Mocks and UI testing.

k6 Open Source is designed for load testing. Extensible to support other types of testing.