API Testing GitHub Repositories (2026) · Open Source Tools

Open-source platform for creating safe, isolated production sandboxes for API, integration, and E2E testing.

Opensource IDE For Exploring and Testing API's (lightweight alternative to Postman/Insomnia)

Catch API bugs before your users do

Open-Source API Development Ecosystem • https://hoppscotch.io • Offline, On-Prem & Cloud • Web, Desktop & CLI • Open-Source Alternative to Postman, Insomnia

Hurl, run and test HTTP requests with plain text.

Terminal API client for HTTP, GraphQL, gRPC, WebSocket and SSE. Plain .http files you can diff and version, with scripted tests, workflows, mocks, recorder, and a CLI runner for CI.

Fast, native API client for REST, gRPC, WebSocket and GraphQL. A local-first Postman alternative written in Go: no Electron, no account, no cloud.

The first open-source AI-driven tool for automatically generating system-level test cases (also known as fuzzing) for web/enterprise applications. Currently targeting whitebox and blackbox testing of Web APIs, like REST, GraphQL and RPC (e.g., gRPC and Thrift).

Simulate API failures, throttling, and chaos — all from your command line.

The open source, cloud native tool for API Mocking and Testing. Microcks is a Cloud Native Computing Foundation incubating project 🚀

Test Automation Made Simple

The Open Source Test Automation Platform.

A TypeScript-native acceptance testing framework that gives your Playwright Test, WebdriverIO, or Cucumber test suite the architecture it needs to scale.

Nimbus automatically analyzes your routes and validation rules to build interactive request schemas and a native interface for testing and exploring your APIs

Free, open-source API testing desktop app built with Rust. No account, no cloud, no telemetry.

.NET Assertions for HTTP APIs

A sandbox for the third-party APIs you depend on. Built from the provider's spec, it fails on purpose, and it replays the exact failure production hit.

Getman - Open Source Postman Lightweight Alternative written in Rust.

Open-source OpenAPI mock server with cloud hosting and local modes for development, testing, and CI. Generates realistic API responses from specs with latency simulation, error injection, proxy fallback, and request validation. Validated against 2,200+ real-world OpenAPI specs.