Top 10 API Testing Clients for Developers in 2025

APIs are the backbone of modern software development. From microservices to mobile apps, from SaaS platforms to IoT — APIs run the show. And whether you're building them or consuming them, you need reliable tools to design, test, debug, and document them efficiently.

In 2025, the market is full of feature-rich API testing clients. Some focus on ease of use, others on automation and collaboration. But which ones actually help you move fast, catch issues early, and ship with confidence?

In this article, we break down the top 10 API testing clients for developers in 2025, starting with one of the fastest-growing platforms: Apidog.

1. Apidog — The All-in-One API Design & Testing Platform

Apidog is quickly rising to become one of the most complete API development clients on the market. It merges the strengths of Postman, Swagger, and Mock tools into one streamlined interface.

Key Features:

• Design-first API development using OpenAPI standards
• Built-in mock server for front-end and back-end parallel development
• Powerful test scripting with pre/post request scripts
• Auto-generated API documentation

Team collaboration with role management and version control

Apidog’s interface is intuitive and fast. It works seamlessly for solo developers as well as large teams looking to unify their API workflow.

Why Apidog Stands Out in 2025:

• Combines multiple tools into one
• Great for both REST and GraphQL
• Ideal for startups and scaling dev teams

Continually evolving with AI-based enhancements

2. Postman — The Industry Standard (But Heavier)

Postman is still one of the most well-known API tools, and for good reason. It offers a mature platform with a huge community and enterprise-grade features.

Key Features:

• Create and send HTTP requests with ease
• Collection runners for automated testing
• Monitor APIs and set up CI/CD integrations
• Public and private workspaces for teams

While Postman is robust, some developers in 2025 are finding it bloated or slow, especially for quick tasks or local-only use.

Best for: Enterprises, teams already deep into the Postman ecosystem

3. Insomnia — Sleek and Developer-Focused

Insomnia is an open-source API client known for its beautiful interface and developer-friendly design. Now backed by Kong, it supports REST, GraphQL, and gRPC.

Key Features:

• Elegant request building and testing
• Environment variables and code generation
• Plugin support and CLI options
• Native Git sync for teams

Insomnia is lighter and more customizable than Postman, making it a favorite for developers who want full control.

Best for: Developers who want a polished, fast alternative to Postman

4. Hoppscotch — The Open Source, Blazing-Fast Option

Originally a browser-based Postman clone, Hoppscotch (formerly Postwoman) has evolved into a powerful, open-source API testing client.

Key Features:

• Lightweight, no-install browser interface
• REST, GraphQL, WebSocket support
• Team collections and history sync

- Offline mode and PWA capabilities

While it’s not as feature-heavy as Apidog or Postman, it’s excellent for quick tests and rapid workflows.

Best for: Developers who want a fast, free, browser-first API client

5. Thunder Client — Lightweight API Testing for VS Code

Thunder Client brings API testing directly into your favorite IDE: Visual Studio Code. It's ideal for developers who don’t want to leave their editor.

Key Features:

• VS Code extension with intuitive UI
• Environment variables and collections
• Lightweight and fast
• Suitable for REST and GraphQL

It’s not as comprehensive as Apidog or Postman, but it’s a great in-editor companion.

Best for: VS Code power users who want quick access to API tools

6. Paw — The API Client for macOS

Paw is a native macOS application that combines beautiful design with powerful features.

Key Features:

• Visual HTTP request composer
• Advanced cookie and auth handling
• Dynamic values and testing workflows
• Export to Swift, Python, and cURL

While it's macOS-only, Paw offers a premium experience for API developers who prefer desktop tools.

Best for: Mac devs looking for a native, full-featured client

7. Katalon Studio — API + UI Testing Automation

Katalon Studio is a test automation platform that supports not only APIs, but also web, mobile, and desktop apps.

Key Features:

• Supports REST, SOAP, and GraphQL
• Data-driven testing
• Built-in reporting and analytics
• Easy CI/CD integration

Its test recorder and codeless automation features make it accessible even for QA teams without deep coding experience.

Best for: QA engineers and teams needing end-to-end automation

8. SwaggerHub — API Design & Docs, Powered by OpenAPI

SwaggerHub is the official platform from SmartBear for building and documenting APIs using OpenAPI specifications.

Key Features:

• API design with real-time collaboration
• Hosted API docs
• Versioning and standard enforcement
• Integrates with tools like GitHub, Jenkins, and Apigee

SwaggerHub is not focused on testing, but it's a crucial piece for companies investing in design-first development.

Best for: Teams prioritizing OpenAPI-first design and governance

9. Rest Assured — Automated Testing for Java Devs

For developers working in Java, Rest Assured provides a powerful library to write automated API tests with fluent syntax.

Key Features:

• Works seamlessly with JUnit or TestNG
• Easy validation of REST responses
• Integration with CI/CD pipelines

It’s not a GUI client, but it’s a must-have for back-end teams focused on automated integration testing.

Best for: Java-based back-end teams and test engineers

10. JMeter — Load Testing + API Validation

While originally built for performance testing, Apache JMeter is widely used to test APIs under load and ensure scalability.

Key Features:

• Simulate thousands of virtual users
• API request building and assertion support
• Supports REST, SOAP, JDBC, and more
• Robust reporting and charts

If you're building high-traffic applications, JMeter helps ensure your APIs can handle the pressure.

Best for: Performance testing and large-scale load simulations

Final Thoughts

In 2025, API development is faster, smarter, and more collaborative than ever before. Whether you're a solo developer shipping MVPs or part of a QA team managing massive test suites, there's a client that fits your flow.

Apidog earns its top spot by providing an all-in-one experience that simplifies everything from design to deployment. But each tool in this list has its strengths — from Postman's dominance to Hoppscotch’s speed to Katalon's automation prowess.

TL;DR – Best API Testing Clients by Use Case:

Whatever your workflow looks like — from building quick prototypes to scaling enterprise APIs — the tools on this list are designed to help you test smarter, ship faster, and build with confidence.

And if you're just starting out or rethinking your stack, don’t overlook the power of an integrated platform that keeps everything in one place.