API Testing

Hoppscotch80.5k★

Hoppscotch does Postman's job in a browser tab. REST, GraphQL, WebSocket, Server-Sent Events, MQTT, and Socket.IO in one place, with environment variables, pre-request scripts, test assertions, and collections. Open the page and start testing. MIT licensed, no download, no account for the free tier. Running in a browser is the whole point. It works on a Chromebook, on a locked-down corporate laptop, on any machine where you cannot install software. For your own copy, the community edition is a Docker deployment that stays free, with your collections on your server instead of somebody else's. The paywall lands where it should. Shared workspaces and admin controls come with the hosted Organization plan at $6 per user a month billed annually. Self-hosted enterprise adds SAML and OIDC single sign-on plus audit logs, and that price is not published. Solo developers and small teams never reach either line. The catch is CORS. A browser tab cannot reach every API, and that is a limit of where the app runs rather than a missing feature. Hoppscotch ships a browser extension and a proxy agent to work around it, which do the job, but it is a step desktop clients like Bruno and Insomnia never ask you to take.

Bruno47.2k★

Bruno stores every API request as a plain text file in your repo. No cloud account, no proprietary collection format. The core app is MIT licensed, runs on Mac, Windows and Linux, and covers REST, GraphQL and gRPC with scripting, environments, assertions and a collection runner. Version 4 added workspaces that group collections, plus an AI assistant for generating docs and autocompleting scripts. The free tier now caps you at two workspaces open at a time. Create as many as you like, just do not expect to open a third. The pricing changed, and not in your favor. The $19 one-time Golden Edition is gone. Pro is $6 per user per month billed annually and adds private Git providers and unlimited workspaces. Ultimate is $11 and adds SSO, SCIM, audit logs and the AI assistant. Solo developers still get a complete client for free. Teams that need SSO now pay per seat, like everyone else. The catch is that not paying a subscription for an API client was Bruno's whole pitch, and that pitch is gone. Gating SSO and audit logs is fair. Capping the MIT-licensed app at two open workspaces is what stings. Compare against Hoppscotch (hoppscotch/hoppscotch) and Insomnia (Kong/insomnia) before committing.

Insomnia40.0k★

Insomnia is a desktop API client for designing, debugging, and testing REST, GraphQL, gRPC, and WebSocket APIs, organized into collections. It's a workbench for APIs: REST, GraphQL, gRPC, and WebSockets all in one interface. You build a request (set the URL, headers, body), hit send, and see the response with syntax highlighting and formatting. Environment variables let you switch between dev/staging/production with one click. Collections keep your API endpoints organized by project. Insomnia went through a rough patch. Kong (the company) added mandatory cloud sync and login requirements, then walked it back after community backlash. The current state: you can use Insomnia locally without an account (Scratch Pad mode), but collaboration features require Kong's cloud. Free tier includes basic request building and local storage. Paid tiers ($5-12/user/mo) add team sync, Git integration, and AI features. The catch: the trust damage from the forced cloud login hasn't fully healed. Bruno, an open source API client that stores collections as plain files in your git repo, emerged directly because of Insomnia's missteps. If you want an API client that will never require a login or cloud sync, Bruno is the answer. Insomnia is more polished and feature-rich, but the community's trust is conditional.

karate9.0k★

Karate is a single tool for API tests, mocks, performance tests, and UI automation. Tests read like English (Given/When/Then) so non-programmers can contribute without learning Java. MIT-licensed, the framework itself is completely free. Runs on the JVM, which means JDK 8+ and Maven or Gradle in your pipeline. No separate test runner, no step definition files like in vanilla Cucumber, no Selenium WebDriver contortions. A test is a .feature file that hits an endpoint, asserts the response, and moves on. Mocking HTTP services is built in, so you can spin up a fake dependency in three lines. QA teams with a mix of engineers and non-engineers get a language they can both write. Devs using Java/Kotlin/Groovy stacks get something that fits their build system. Karate Labs sells training and an enterprise UI layer, but the open source tool does the full job. The catch: the DSL looks like Gherkin but is not. You cannot share feature files with a standard Cucumber pipeline, and if your team is already deep in REST Assured or Playwright, switching frameworks to get slightly better readability rarely pays for itself.

mockoon8.4k★

Mockoon spins up a fake API on your machine in about thirty seconds. You define routes, status codes, headers, and response bodies in a desktop app, hit start, and your frontend has something to talk to while the real backend is still being written. No account, no signup wall, no deployment step. The desktop app and the CLI are both MIT. Running it yourself is the normal path, not the fallback. The CLI ships as an npm package and a Docker image, so the same mock you built on your laptop runs headless in CI. Definitions are JSON files you commit to git. Dynamic templating, proxy forwarding, request recording, HTTPS, and stateful CRUD endpoints are all in the open source build. Solo developers and small teams are fully covered by the free build. Mockoon Cloud is $100 per month billed annually for five seats, three deployed mocks, and 100,000 monthly calls, and what you are buying is the shared workspace: a web app, real-time collaboration, automatic sync, hosted mock URLs, and next business day support. Worth it when passing JSON files around stops scaling. Compare against Hoppscotch (hoppscotch/hoppscotch) and Bruno (usebruno/bruno) if you want one tool for both calling and mocking. The catch is that sharing is the paywall. Git syncs definitions fine, but there is no free hosted instance, so the moment QA or a client needs a URL they can hit, you are either paying or standing the CLI up on a box yourself.

thunder-client-support3.7k★

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. 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. 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.

insomnia-mockbin2.1k★

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 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.

api-gateway644★

Membrane is a lightweight Java-based API gateway for authentication, request transformation, and routing. It sits between your clients and your backend services, inspecting and modifying requests as they flow through. It can check authentication, throttle abusive clients, rewrite URLs, transform XML to JSON, and route traffic to different backends based on rules. The configuration is XML-based (this is a Java project, after all). Membrane has been around since 2011 and is open source under Apache 2.0. It's a niche tool with a small but committed community. No paid tier, no cloud service. The catch: this is old-school Java middleware. If you're in a modern cloud-native stack, Traefik or Kong are better choices with larger communities, better documentation, and Kubernetes integration. Membrane works but it feels like enterprise software from a different era. Unless you have a specific need for Membrane's SOAP/WSDL handling (it's strong there) or you're already in a Java shop, there are better options.