Top 7 Free API Clients for 2025

API clients help developers interact with APIs, test endpoints, and debug issues without writing custom scripts from scratch. As APIs grow more complex, a reliable API client can save time and reduce errors by simplifying how developers work with APIs.

This article explores the seven best and free API clients in 2025. But before that, it’s important to understand the basics.

What is an API Client?

An API client is a tool that allows developers to send requests to an API and view the responses. API clients let developers interact with APIs using HTTP methods like GET, POST, PUT, and DELETE. They take care of the request and response process, making it easier to understand how an API behaves.

API clients can be browser-based, desktop applications, or command-line tools. They support different formats like JSON, XML, and text responses, and can be configured to work with various authentication methods. The main purpose of an API client is to give developers a simple way to test and debug APIs without relying on their main application.

How to Choose an API Client?

When choosing an API client, developers should consider several factors to make sure the tool meets their needs:

• Request builder: Ensure it supports all the HTTP methods you use and lets you set headers, parameters, and request bodies easily. This matters because a flexible request builder saves time and makes testing different scenarios simpler.
• Response parser: Look for a client that formats and displays API responses clearly, so you can debug and verify data without extra steps. This helps you catch errors quickly and understand what’s going on in each API call.
• Authentication support: Check if the client handles authentication methods like API keys, OAuth, and basic auth, which are often required in real-world APIs. Proper support avoids headaches and lets you test exactly how your app would work in production.
• Extensibility: Find out if you can extend the client’s functionality with plugins, scripting, or integrations with your workflow. This is important for advanced testing and for adapting the client to your team’s needs.
• Performance: Make sure it runs smoothly and doesn’t slow down your system, even with large collections or complex APIs. A lightweight tool ensures you can work efficiently without waiting for the client to catch up.

• Protocol support: Confirm that the client supports the API protocols you work with, such as REST, GraphQL, or gRPC. This is crucial because it ensures you can test and debug all the APIs your app depends on, not just the common ones.

List of 7 Best Free API Clients

These tools were chosen based on their ability to support core API testing features, handle different API protocols, and provide a reliable experience for developers and testers.

1. Requestly

Requestly is a versatile API client and debugging tool that runs in the browser or as a desktop app. It’s designed to help developers and testers modify, intercept, and debug HTTP requests with ease.

Unlike some other API clients that focus solely on sending requests and viewing responses, Requestly also allows you to manipulate how those requests work, which can be helpful in testing and troubleshooting APIs.

Key Features of Requestly

• Intercept and modify HTTP requests and responses in real time
• Mock APIs by creating custom rules for different endpoints
• Redirect, cancel, or replace requests
• Inspect network traffic for better debugging
• Browser extensions for quick access
• Desktop app for more advanced use cases

Key Benefits of Requestly

• Flexible Testing and Debugging: Modify requests and responses in real time to explore different scenarios and edge cases without changing your main application.
• Detailed Network Insights: Inspect every part of the request and response to catch issues and optimize your APIs.
• Fast Setup: Start testing instantly in the browser or the desktop app with no complicated installation or extra tools needed.
• Precise Control: Create custom rules for specific endpoints to see how your application handles different responses or errors.
• Consistent Workflow: Use the same tool for request modification and API testing to avoid context switching and save time.

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2. Postman

Postman is an API client that focuses on helping developers organize and run HTTP requests in a structured way. It lets users group their requests into collections and test different scenarios using environment variables and automated scripts.

Key Features of Postman

• Supports REST API, GraphQL, and WebSocket APIs
• Collection-based organization
• Environment variables for switching between setups
• Automated tests with JavaScript-based scripting
• Visual interface for building and managing requests

Limitations

• Can use significant memory and CPU resources for larger setups
• Interface can feel cluttered for new users
• Occasional issues with syncing data across devices

3. Hoppscotch

Hoppscotch is a web-based API client built for quick and straightforward API testing. Its browser-first approach helps developers send and view API requests without installing software, making it ideal for quick tests or lightweight development work.

Key Features of Hoppscotch

• Supports REST, GraphQL, and WebSocket APIs
• Lightweight and fast interface
• Environment and dynamic variable support
• Code snippets for common languages
• Open-source project with active updates

Limitations

• Limited advanced testing or scripting tools
• No desktop app version
• Fewer integrations with other development tools

4. Insomnia

Insomnia is a desktop application designed for testing APIs with a focus on keeping requests, environments, and projects neatly organized. It’s suitable for developers who need to manage multiple APIs or different stages of development.

Key Features of Insomnia

• Supports REST, GraphQL, and gRPC APIs
• Environment-specific request handling
• JSON and XML response formatting
• Plugin system for extensions
• Workspace organization for larger projects

Limitations

• Collaboration features are only in paid plans
• Only works as a desktop app
• Some stability issues reported on certain platforms

5. Thunder Client

Thunder Client runs inside Visual Studio Code as an extension, giving developers a way to send and manage REST API requests directly from their editor. It’s designed for developers who want a lightweight tool without leaving their coding environment.

Key Features of Thunder Client

• REST API testing inside Visual Studio Code
• Environment variables for different setups
• Basic automated testing and response visualization
• Import and export of collections

Limitations

• Limited to REST APIs
• Works only inside Visual Studio Code
• Lacks advanced automation and scripting features

6. Bruno

Bruno is an open-source, local-first API client for developers who want to test APIs without relying on cloud storage or remote servers. It’s designed to keep data entirely on the developer’s machine.

Key Features of Bruno

• Local-first storage for privacy
• Environment support for different setups
• Workspace and collection organization
• Minimalistic, fast interface
• Open-source and actively maintained

Limitations

• Only available as a desktop app
• Fewer integrations with developer tools
• Limited advanced testing features in early development

7. HTTPie

HTTPie is a command-line tool that aims to make HTTP requests simpler and more readable for developers. It’s built for those who prefer working in the terminal and want clear, color-coded output for quick API debugging.

Key Features of HTTPie

• Command-line interface for making HTTP requests
• Syntax highlighting for clear JSON and text output
• Support for REST and GraphQL APIs
• Useful in scripts and automation tasks
• Open-source and community-supported

Limitations

• No graphical interface, terminal-only
• Basic testing tools without automation
• No built-in collaboration features

Conclusion

API clients help developers and testers work with REST APIs by providing a simple way to send requests, view responses, and catch issues early. They make it easier to test endpoints in different environments and ensure applications work as expected.

Requestly stands out as an API client and debugging tool as it combines a request builder, response parser, and request modification features in one platform. Developers can intercept and modify requests in real time and test different scenarios without changing their applications.

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