Yaak

HTTPie

HTTPie is an API testing client built around simplicity, offering an open-source command-line tool alongside a Desktop application currently in public beta. The CLI is installable through common package managers including apt, brew, pip, snap, and choco, and has built up a large open-source community with nearly 48,000 GitHub stars.

Insomnia

Insomnia is a developer‑focused tool that lets you design, debug, and document APIs from a single, intuitive interface. It runs on Web, Windows, macOS, and Linux, providing a consistent experience wherever you work. With a freemium model, Insomnia offers robust features for individual developers and entire API teams, including collaboration, environment management, and seamless integration with popular API gateways and services.

Thunder Client

Thunder Client is a REST API testing extension that runs inside VS Code and JetBrains IDEs, letting developers send requests and inspect responses without leaving their editor or switching to a separate app like Postman. Collections and environments are stored locally, and can be synced to a team's own Git repository for version-controlled collaboration. Beyond manual request testing, Thunder Client supports scripted assertions, WebSocket, SSE, and gRPC testing, and a CLI for running collections inside CI/CD pipelines. It has been downloaded more than six million times since launching in 2021, positioning itself as a lighter, IDE-native alternative to standalone API clients.