Testing APIs manually with browser dev tools is tedious and error-prone. Dedicated API testing tools let you build, save, and share request collections, handle authentication flows, and automate test sequences. Here are the best free options available in 2025.
Postman (Free Tier)
Postman remains the most popular API testing tool. The free tier supports unlimited requests, collections, and environments. Request history, variable substitution, and pre/post-request scripts are all included. The major limitation of the free tier is limited collaboration – shared workspaces require a paid plan.
Thunder Client (VS Code)
A lightweight REST API client built into VS Code. No separate application to install. Supports collections, environments, variables, and basic scripting. Response times and sizes are displayed inline. For developers who prefer staying in their editor, Thunder Client eliminates context switching.
Insomnia
Open-source API client with an excellent interface for REST and GraphQL APIs. The design-first approach includes OpenAPI spec editing, request chaining, and environment management. Insomnia handles authentication flows (OAuth 2.0, API keys, Bearer tokens) cleanly with built-in helpers.
Bruno
A newer open-source API client that stores collections as plain text files in your Git repository. No cloud sync, no account required. Collections use a simple markup language called Bru. For teams that want API collections versioned alongside their code, Bruno is the best current option.
HTTPie
Command-line HTTP client designed for human readability. Syntax is simpler than curl: http POST api.example.com/users name=John. Supports JSON by default, colorized output, sessions, and plugins. The desktop app adds a GUI with request history. See also our form validation guide for testing form submissions.
curl
The universal HTTP tool. Available on every operating system. Not the friendliest interface, but the most portable and scriptable. Every API documentation includes curl examples. Learn the basics: -X for method, -H for headers, -d for data, -v for verbose output.