API Testing

4 open source tools compared. Sorted by stars — scroll down for our analysis.

Tool	Stars	Velocity	Language	License	Score
Hoppscotch Open source API development ecosystem	78.7k	—	TypeScript	MIT License	82
Bruno Open source IDE for exploring and testing APIs	42.4k	—	JavaScript	MIT License	79
thunder-client-support	3.7k	+3/wk		—	61
insomnia-mockbin	2.0k	—	JavaScript	—	61

Our Analysis

Hoppscotch78.7k★

If you test APIs and want something that runs in your browser with zero installation — or self-host it for your whole team — Hoppscotch is a web-first API development platform. REST, GraphQL, WebSocket, SSE, MQTT, and Socket.IO all in one tab. Open it, start testing. No download, no account required for the free version. 78K stars. MIT licensed. The interface is fast and clean. Features include environment variables, pre-request scripts, test assertions, collections, and a team workspace. The browser-based approach means it works everywhere — Chromebook, locked-down corporate laptop, whatever. Self-hosted community edition is free (Docker). The cloud version and self-hosted enterprise add team features: shared workspaces, admin controls, SSO. Enterprise pricing isn't publicly listed — you need to contact them. The catch: the browser-based approach has a fundamental limitation — CORS. Some APIs can't be reached from a browser tab. Hoppscotch offers a browser extension and a proxy agent to work around this, but it's an extra step that desktop apps like Bruno or Insomnia don't need.

Bruno42.4k★

If you test APIs and hate that Postman went cloud-first, Bruno is the answer. It's an API client that stores everything in plain text files on your filesystem — no cloud sync, no account required, no collections locked in a proprietary format. Your API requests live in Git alongside your code. 42K stars. MIT licensed. Supports REST, GraphQL, and gRPC. Has scripting (pre-request and post-response), environment variables, assertions, and collection runners. The desktop app runs on Mac, Windows, and Linux. Bruno Golden Edition is $19 one-time (not a subscription) and adds visual Git diff for collections, secrets management, and a few quality-of-life features. That's it — one payment, forever. The filesystem-first approach is genuinely different. Your team commits .bru files to the repo, reviews API changes in PRs, and never worries about syncing collections across accounts. No lock-in. Export is just... copying files. The catch: the ecosystem is smaller than Postman's. Fewer integrations, fewer tutorials, smaller plugin library. If you rely on Postman's monitoring, mock servers, or team workspace features, Bruno doesn't replace all of that. And gRPC support is still maturing.

thunder-client-support3.7k★

If you test APIs and don't want to leave VS Code, Thunder Client is an HTTP client that lives in your editor's sidebar. Send requests, inspect responses, organize them into collections — like Postman but without opening another application. For developers who spend their day in VS Code, that integration matters more than you'd think. The free version covers the basics: send requests, save collections locally, environment variables, and basic scripting. It's fast, lightweight, and doesn't need an account to use. The paid tier at $10/mo (or $8.33/mo billed annually at $100/yr) adds Git sync for collections, team collaboration, CI/CD integration, and advanced scripting. There's also a per-seat Team plan. The catch: the free tier has gotten more restrictive over time. Features that were once free are now behind the paywall. Collection storage limits apply on free. And unlike Postman's massive ecosystem, Thunder Client's scripting and testing capabilities are more limited. If you outgrow it, you're migrating collections. Bruno is the best open source alternative — offline-first, stores collections as files in your repo, no account needed ever. Hoppscotch is another strong free option with a modern web UI. If you're deep in the Postman ecosystem already, the switching cost may not be worth it. But if you're starting fresh and live in VS Code, Thunder Client's integration is hard to beat.

insomnia-mockbin2.0k★

Mockbin lets you create fake API endpoints that return whatever response you define. If you're building an app that talks to an API that doesn't exist yet, or you need to test how your code handles different HTTP responses (errors, timeouts, weird headers), Mockbin gives you a URL that acts like that API. It's the testing utility behind Insomnia (Kong's API client). You define a response — status code, headers, body — and get a public URL that returns it. Also logs incoming requests so you can inspect what your app actually sent. This specific repo is the open source Mockbin service. You can self-host it or use the hosted version through Insomnia. The project itself is small (2k stars) and development is minimal — it's a utility, not a platform. The catch: Mockbin is a small piece of the Insomnia ecosystem. Insomnia itself is where the real API testing workflow lives, and Insomnia's pricing has gotten complicated since Kong acquired it. The free Insomnia tier works for basic use. If you just need mock endpoints, Mockbin standalone is fine. But if you want a full API development workflow, look at Bruno (free, open source) or Hoppscotch.