12 Best API Testing Tools for Developers in 2026

I spend an unreasonable amount of time hitting APIs. Building them, testing them, debugging them when they break at 2 AM because someone pushed a schema change without telling anyone. Over the years I've used just about every API testing tool that exists, and most of them are fine. Fine isn't good enough when you're staring at a 500 error and your deploy is blocked.

The API testing tool landscape has changed a lot in the last two years. Postman got more expensive and more bloated. A wave of open-source alternatives showed up with genuinely good ideas. Some tools that were niche picks in 2024 have become mainstream. Others that were popular faded because they stopped innovating.

This list is opinionated. I'm not giving you a neutral comparison chart. I'm telling you what I'd actually use, what I'd recommend to different types of developers, and which tools aren't worth your time despite the marketing. If you disagree with my rankings, good. That means you've actually used these tools too.

1. Postman

What it does: The Swiss Army knife of API testing. REST, GraphQL, WebSocket, gRPC, SOAP. If there's a protocol, Postman probably supports it.

Why it's still number one: I know some developers are going to roll their eyes at this pick. Postman has gotten bloated. The free tier keeps shrinking. The UI has more features crammed into it than a Tesla dashboard. But here's the thing: Postman is still the tool that most teams standardize on, and for good reason. The collection sharing, environment management, and test scripting are mature in a way that newer tools haven't matched yet. When you join a new team and they hand you a Postman collection with 200 endpoints already configured, you understand the value. The new AI features for auto-generating tests from your API specs are genuinely useful too. Not gimmicky, actually useful.

Best for: Teams that need collaboration features, developers working with complex API ecosystems, anyone who values a massive community and tons of learning resources.

Pricing: Free tier available. Basic starts at $14/month per user. Professional is $29/month. Enterprise runs $49/month.

Link: postman.com

Pro tip: Use Postman's Pre-request Scripts to chain API calls together. Set a variable in one request's test script, reference it in the next request's URL or body. It turns a flat collection into an automated workflow. Most developers never touch this feature and they're missing out.

2. Bruno

What it does: An open-source API client that stores your collections as plain files in a Git-friendly format called Bru.

Why it made the list: Bruno is the tool I'd build if I started from scratch today. Every collection lives as files on your filesystem. That means you commit them to Git alongside your code. No cloud sync, no account required, no wondering who changed what in the shared workspace. When your teammate updates an API endpoint, the collection change shows up in the same pull request as the code change. That's how it should work. The Bru markup language is clean and human-readable, so you can actually diff collections in code review. Bruno has grown fast too. It went from a curiosity project to over 30,000 GitHub stars and serious adoption in under two years.

Best for: Developers who want their API collections version-controlled. Teams that are tired of Postman's pricing. Privacy-conscious developers who don't want collections synced to someone else's cloud.

Pricing: Free and open source. The Golden Edition with extra features is a one-time $19 payment. No subscription.

Link: usebruno.com

Pro tip: Import your existing Postman collections into Bruno with one click. It converts them to Bru format automatically. You can migrate an entire team's collection library in an afternoon.

3. Hoppscotch

What it does: A lightweight, blazing-fast API development platform that runs in your browser or as a desktop app.

Why it made the list: Speed. That's the short answer. Hoppscotch loads instantly, sends requests instantly, and gets out of your way. When I need to quickly test an endpoint and I don't want to wait for Postman to boot up and sync, I open Hoppscotch. It supports REST, GraphQL, WebSocket, SSE, Socket.IO, and MQTT out of the box. The interface is minimal in the best possible way. No feature bloat, no marketing banners, just a clean request builder. The self-hosted option is solid for teams that need to keep everything on their own infrastructure. The open-source community behind it is active and responsive.

Best for: Developers who want speed and simplicity. Quick ad-hoc testing. Teams that want a self-hosted solution. Anyone who finds Postman too heavy for everyday use.

Pricing: Free and open source. Self-hosted enterprise version available.

Link: hoppscotch.io

Pro tip: Use keyboard shortcuts religiously. Ctrl+Enter sends the request. Ctrl+S saves to a collection. Once you learn the shortcuts, you can fly through API testing without touching the mouse.

4. Thunder Client

What it does: A REST API client that lives inside VS Code as an extension.

Why it made the list: If you live in VS Code (and most of us do), context switching to a separate app for API testing is friction you don't need. Thunder Client puts a full API testing interface right in your editor sidebar. You're writing code, you need to test the endpoint you just built, you click the Thunder Client icon, fire off a request, see the response, and you're back to coding. No alt-tabbing, no waiting for another app to load. The interface is clean and Postman-like enough that there's almost no learning curve. It handles environments, collections, and even basic scripting. For solo developers or small teams, it might be all you ever need.

Best for: VS Code users who want API testing without leaving their editor. Solo developers. Quick endpoint validation during development.

Pricing: Free for individual use. Pro plan at $10/month for team features and advanced scripting.

Link: thunderclient.com

Pro tip: Enable the Git sync feature to save your collections as JSON files in your project. It works similarly to Bruno's file-based approach but stays inside VS Code.

5. Insomnia

What it does: A desktop API client with strong support for REST, GraphQL, gRPC, and WebSocket testing.

Why it made the list: Insomnia has had a rocky couple of years. Kong acquired it, made some unpopular decisions with cloud-only sync, the community got mad, and they had to walk it back. That drama aside, the core product is still excellent. The GraphQL support is the best of any tool on this list. Auto-completion of queries based on your schema, inline documentation, and proper variable support make working with GraphQL APIs a pleasure instead of a chore. The environment chaining and template tags for dynamic values are more intuitive than Postman's scripting approach. If your stack is heavy on GraphQL, Insomnia deserves a serious look.

Best for: GraphQL-heavy teams. Developers who want a cleaner UI than Postman. Anyone who values good keyboard-driven workflows.

Pricing: Free for individuals. Team plans start at $12/month per user.

Link: insomnia.rest

Pro tip: Use the Git Sync feature with a local repository. It gives you version control over your API collections without relying on Insomnia's cloud, and it survived all the ownership drama because your data stays local.

6. HTTPie

What it does: A command-line HTTP client with an optional desktop GUI, designed to make API interaction feel natural.

Why it made the list: There's a certain type of developer who does everything in the terminal. I respect that. cURL is the default, but cURL's syntax is hostile. Try remembering the difference between -d, --data-binary, and --data-urlencode at 11 PM. HTTPie fixes this with a syntax that reads like English. http POST api.example.com/users name=John age:=30. That's it. Strings get quotes, numbers get :=, and headers use :. The colorized output with automatic JSON formatting means you can actually read responses without piping through jq. The desktop app adds a visual interface if you need it, but the CLI is where HTTPie shines.

Best for: Terminal-first developers. Quick one-off requests. Scripting API calls in shell scripts. Anyone who's tired of cURL's syntax.

Pricing: CLI is free and open source. Desktop app has a free tier with paid plans for teams.

Link: httpie.io

Pro tip: Use HTTPie sessions to persist headers and auth across requests. http --session=myapi api.example.com/login saves your auth token, and every subsequent request with that session name includes it automatically.

7. REST-assured

What it does: A Java library for testing RESTful APIs with a fluent, readable syntax that integrates directly into your test suite.

Why it made the list: Every other tool on this list is a standalone app or extension. REST-assured is different. It's a library you add to your Java project, and it lets you write API tests as code. That means your API tests run in CI/CD alongside your unit tests. No separate tool to maintain, no manual clicking. The fluent syntax is genuinely elegant: given().auth().basic("user","pass").when().get("/api/users").then().statusCode(200). It reads like a sentence. For Java and Kotlin teams, REST-assured is often the right answer because it fits into existing test infrastructure without adding another tool to the stack.

Best for: Java and Kotlin developers. Teams that want API tests in their CI pipeline. Projects where API testing needs to be part of the automated test suite, not a separate manual process.

Pricing: Free and open source (Apache 2.0 license).

Link: rest-assured.io

Pro tip: Combine REST-assured with JsonPath assertions for deep validation of nested JSON responses. You can validate specific fields at any depth without parsing the entire response manually.

8. Karate DSL

What it does: An open-source framework that combines API testing, mocking, performance testing, and UI automation in a single tool using a BDD-style syntax.

Why it made the list: Karate is the Swiss Army knife for teams that need more than just "send a request, check the response." You write tests in a Gherkin-like syntax that non-developers can read, but it's powerful enough for complex test scenarios. The killer feature is built-in parallel execution and performance testing. You write a functional API test, then reuse it as a performance test with a single configuration change. No separate load testing tool required. Karate also generates HTML reports automatically, which makes it easy to share results with non-technical stakeholders. It runs on the JVM, so it fits naturally into Java ecosystems, but you don't need to write any Java code to use it.

Best for: Teams that need API testing and performance testing in one tool. QA engineers who want readable test syntax. Java-ecosystem projects that want comprehensive API test coverage.

Pricing: Free and open source (MIT license).

Link: github.com/karatelabs/karate

Pro tip: Use Karate's built-in mock server feature to create API mocks for testing. You can define mock responses inline in your test files, which means your tests don't depend on external services being available.

9. k6 by Grafana

What it does: A load testing and performance testing tool where you write test scripts in JavaScript.

Why it made the list: Most API testing tools on this list focus on functional testing. Does the endpoint return the right data? k6 answers a different question: does the endpoint still return the right data when 10,000 users hit it simultaneously? I'm including k6 because too many developers only think about API testing as "does it work" and never ask "does it work under load." k6 scripts are plain JavaScript, so there's no new language to learn. You define scenarios, set virtual user counts, and k6 generates real HTTP traffic against your endpoints. The output integrates with Grafana dashboards for beautiful real-time visualization. Developer experience is where k6 separates itself from older tools like JMeter. Writing a k6 script feels like writing code. Writing a JMeter test plan feels like configuring an enterprise application from 2003.

Best for: Performance and load testing. Teams that need to validate API behavior under stress. Developers who want performance tests in their CI pipeline.

Pricing: CLI is free and open source. Grafana Cloud k6 offers managed cloud execution starting at free tier.

Link: k6.io

Pro tip: Use k6's check() function to add assertions to your load tests. This way you're testing both performance AND correctness under load. A fast response that returns wrong data is worse than a slow correct one.

10. Swagger UI / Swagger Editor

What it does: An interactive API documentation and testing interface generated directly from your OpenAPI specification.

Why it made the list: Swagger UI isn't a traditional API testing tool. But if you're building APIs (and that's most backend developers), Swagger UI gives you something nothing else on this list does: testable documentation that stays in sync with your code. You annotate your API endpoints, Swagger generates an interactive page where anyone can try the endpoints with real data. No Postman collection to maintain separately. No documentation that drifts out of date. When someone changes an endpoint, the Swagger docs update automatically because they're generated from the same source. For internal APIs where your consumers are other developers on your team, Swagger UI might be the only "testing tool" you need.

Best for: API producers who want self-documenting, testable APIs. Teams where the API spec is the source of truth. Internal tool development where separate testing tools add unnecessary overhead.

Pricing: Free and open source. SwaggerHub (the hosted platform) has paid plans starting at $95/month per team.

Link: swagger.io/tools/swagger-ui

Pro tip: Add the x-codeSamples extension to your OpenAPI spec to include copy-paste-ready code examples in multiple languages right in your Swagger UI. Your API consumers will love you for it.

11. Katalon Studio

What it does: A comprehensive test automation platform that handles API, web, mobile, and desktop testing in one tool.

Why it made the list: Katalon is the tool you reach for when API testing is part of a bigger testing story. Maybe you need to test a web flow that calls APIs behind the scenes, or you need to validate that a mobile app correctly handles an API response. Katalon lets you mix API tests with UI tests in the same test suite. The built-in keyword-driven approach means less technical testers can build API tests using a visual interface, while experienced developers can drop into Groovy scripting for complex logic. It's not the leanest tool, and it's definitely enterprise-oriented. But if your organization needs a single platform for all types of testing, Katalon does it without duct-taping five tools together.

Best for: QA teams that test across web, mobile, and API layers. Enterprise organizations that want one testing platform. Teams with mixed technical skill levels.

Pricing: Free tier available. Premium plans start at $208/month.

Link: katalon.com

Pro tip: Use Katalon's built-in data-driven testing feature to run the same API test with hundreds of different input combinations from a CSV or database. It's one of the fastest ways to find edge cases in your API validation logic.

12. Stepci

What it does: An open-source API testing and monitoring tool built for CI/CD pipelines, using YAML-based test definitions.

Why it made the list: This is my "lesser-known pick that most lists won't include" entry. Stepci is small, focused, and does one thing really well: automated API testing in your CI pipeline with zero ceremony. You write a YAML file describing your API tests. Request, expected response, done. No GUI, no accounts, no cloud service. Just a CLI that reads a YAML file and tells you if your APIs work. It supports REST, GraphQL, gRPC, tRPC, and SOAP. The YAML syntax is dead simple. It installs via npm. It runs in GitHub Actions, GitLab CI, Jenkins, whatever you use. For developers who believe testing tools should be configuration, not applications, Stepci is exactly right. It has around 4,000 GitHub stars and a small but passionate community.

Best for: Developers who want API tests as code/config in their CI pipeline. Small teams that don't need a GUI. Projects where you want to add API contract testing without a heavy framework.

Pricing: Free and open source (MPL 2.0 license).

Link: stepci.com

Pro tip: Use Stepci's reusable components feature to define common auth flows once and reference them across all your test specs. It keeps your YAML files DRY and maintainable as your API surface grows.

How to Pick the Right Tool for Your Situation

Look, twelve tools is a lot. Let me make this simple.

If you're a solo developer doing quick API tests during development, start with Thunder Client (you're already in VS Code) or Hoppscotch (zero setup, runs in your browser). You don't need Postman's complexity for checking if your endpoint returns the right JSON.

If you're on a team that shares API collections and needs collaboration, Postman is still the safe choice. Everyone knows it, the ecosystem is massive, and it works. If the pricing bothers you or you want Git-based collaboration instead of cloud sync, move to Bruno. The migration path is smooth.

If you work with GraphQL, Insomnia has the best GraphQL experience. Period. The auto-completion and schema-aware features save real time.

If you need API tests in your CI/CD pipeline, the choice depends on your stack. Pairing testing tools with AI coding assistants can speed up test generation. Java teams should look at REST-assured or Karate DSL. Everyone else should consider Stepci for its simplicity or k6 if performance testing matters too.

If you're building APIs and want living documentation, Swagger UI is non-negotiable. It's not either/or with the tools above. Use Swagger for docs and one of the other tools for deeper testing.

Don't overthink this. Pick one tool, learn it well, and switch only when you hit a real limitation. The worst thing you can do is spend three weeks evaluating API testing tools instead of actually testing your APIs.

What I'd Actually Use (My Personal Stack)

Since people always ask: my daily API testing setup is Bruno for collection management (everything in Git), HTTPie for quick terminal requests, and k6 for performance testing before releases. I keep Postman installed for those times when someone sends me a Postman collection, which still happens a lot. When I'm deep in VS Code and don't want to switch contexts, Thunder Client gets the job done.

That's five tools, which sounds like a lot, but each one fills a distinct role. Bruno for organized testing. HTTPie for speed. k6 for performance. Postman for compatibility. Thunder Client for convenience. No overlap, no redundancy.

The API testing tool you use matters less than whether you're actually testing your APIs consistently. The best tool is the one you'll use every day, not the one with the most features on a comparison chart. Start somewhere. Get into the habit. Then optimize your tooling once testing is part of your workflow, not an afterthought. Good testing habits are one of the key skills employers look for and they'll come up in code reviews too.