10 Best REST API Clients and Testing Tools for 2025

REST API clients are tools used to send HTTP requests to interact with RESTful APIs, allowing developers to test, debug, and integrate APIs. They help build and send requests (GET, POST, PUT, DELETE) while handling responses like status codes and body content. These REST clients also support authentication methods and can automate testing. REST API testing tools, like Postman and Insomnia, are essential for ensuring API functionality, performance, and security.

Let’s talk in detail about REST API clients and testing tools below.

What is a REST API?

A REST API (Representational State Transfer Application Programming Interface) is a way for applications to communicate with each other over the web using standard HTTP methods like GET, POST, PUT, and DELETE. It is used to expose data or functionality from one system so that other applications or services can interact with it easily. 

REST APIs are popular because they are lightweight, scalable, and language-independent, making integration between different systems simple. They help developers build flexible applications faster while ensuring seamless connectivity across platforms, devices, and services.

List of 10 Best REST API Clients and Testing Tools

Below is a comprehensive list of the 10 Best REST Clients that you can consider for API testing.

1. HTTPie

HTTPie is a modern, user-friendly command-line HTTP client written in Python. Unlike traditional cURL commands, it focuses on making API testing more intuitive with human-friendly syntax and colorized output, making it a popular choice for developers who prefer working from the terminal.

When testing REST APIs, HTTPie helps simplify sending requests and visualizing responses without complex commands. Its built-in JSON support and syntax highlighting ensure clarity when debugging APIs. For teams that frequently test endpoints, HTTPie reduces friction and boosts productivity.

Key Features:

• Simple, natural syntax for HTTP requests
• Built-in JSON formatting and support
• Syntax highlighting and colorized terminal output
• Support for custom headers, sessions, and file uploads

Pros:

• Very developer-friendly and lightweight
• Great for quick REST API testing directly from the terminal
• Open-source and actively maintained

Cons:

• Lacks advanced collaboration features
• GUI-based users may find the command-line interface intimidating

Read about other Python REST frameworks in 2025.

2. Postman

Postman is one of the most widely used REST API Clients and Testing Tools. It offers a powerful environment where developers can design, send, and test REST API requests through an easy-to-use graphical interface. Over the years, it has evolved from a simple Chrome extension into a complete API development ecosystem.

Postman REST Client helps teams debug APIs, automate test workflows, and monitor API performance in real time. It supports multiple protocols, integrates seamlessly with CI/CD pipelines, and provides collaboration features for sharing collections across teams. For developers and QA engineers, Postman reduces manual effort and improves the efficiency of API development cycles.

Key Features:

• Automated REST API testing and debugging
• Team collaboration with workspaces and shared collections
• Supports Swagger/OpenAPI and RAML specifications
• Built-in test runner and powerful visualization tools
• Cookie and certificate management for secure requests

Pros:

• Beginner-friendly UI with drag-and-drop options
• Advanced automation features for testing at scale
• Strong ecosystem with integrations for CI/CD and DevOps tools

Cons:

• Can be resource-heavy on large projects
• Some advanced features require a paid plan

3. cURL

cURL is a classic free, open-source command-line tool for transferring data with URLs. Originally released in the 1990s, it remains one of the most versatile clients. In simple terms, cURL lets you send HTTP(S) requests from the terminal. It supports almost every network protocol, including HTTP, HTTPS, FTP, FTPS, SFTP, IMAP, POP3, and many more.

Developers often use cURL in scripts or CI jobs to make REST calls, test endpoints, or automate interactions. It’s installed by default on many Unix-like systems, so it’s readily available. Using cURL requires memorizing several flags and syntax, but it gives precise control over every detail of the request.

Key Features:

• Support for multiple internet protocols (HTTP, HTTPS, FTP, SFTP, POP3, SMTP, etc.)
• Complete control over HTTP requests: headers, methods, data, cookies, auth, proxies
• Upload and download files, with resume capability
• SSL/TLS support with certificate options
• Writable to scripts for automation

Pros:

• Portable and pre-installed on many systems
• Free, well-documented, and highly versatile
• Extremely fast and lightweight

Cons:

• Complex syntax for beginners
• Lacks JSON formatting or readability features
• No built-in higher-level API testing functions

4. Swagger

Swagger provides an API design and documentation framework based on the OpenAPI specification. It uses a standard YAML or JSON specification to describe REST APIs, including endpoints, parameters, and schemas.

Swagger helps development teams by keeping API docs in sync with code. With Swagger UI, you can generate an interactive documentation portal where users can test endpoints directly. It also includes tools like Swagger Editor for spec writing and Swagger Codegen for generating client libraries or server stubs.

Key Features:

• OpenAPI-based API specification
• Swagger UI for interactive documentation
• Swagger Editor for writing and validating API definitions
• Code generation for SDKs and server stubs
• Mocking and contract testing support

Pros:

• Industry standard for documenting RESTful APIs
• Auto-generates SDKs and interactive documentation
• Encourages consistent API design practices

Cons:

• Steep learning curve for writing specs
• Does not serve as a full API testing tool on its own
• Large APIs can lead to lengthy specification files

5. Katalon Studio

Katalon Studio is an integrated automation tool for web, mobile, desktop, and API testing. It provides a user-friendly interface where testers can create test cases without extensive programming knowledge.

For REST API testing, Katalon supports REST and SOAP endpoints, test assertions, and data-driven testing. It can also import Swagger definitions or Postman collections. This makes it a powerful solution for QA teams who need an all-in-one tool for multiple testing needs.

Key Features:

• No-code and scripting modes
• Supports REST and SOAP APIs
• Import Swagger/OpenAPI and Postman collections
• Built-in reporting and CI/CD integration
• Cross-platform compatibility

Pros:

• Accessible for both testers and developers
• Free to use with powerful built-in features
• Consolidates API, web, and mobile testing in one tool

Cons:

• Not open source
• Heavy on resources for large projects
• Paid features required for advanced usage

6. SoapUI

SoapUI is an open-source tool designed specifically for API testing, supporting both REST and SOAP services. It has long been a staple in the API testing ecosystem.

SoapUI allows for drag-and-drop test creation, data-driven testing, and even security and load testing. It also supports mocking services, enabling development even when APIs aren’t fully ready.

Key Features:

• Supports REST, SOAP, GraphQL, JMS, JDBC, and more
• Built-in assertions for JSON/XML
• Data-driven testing with external sources
• Security and load testing features
• Mocking and service virtualization

Pros:

• Free and widely adopted with a strong community
• GUI-driven test design without coding
• Supports multiple protocols beyond REST

Cons:

• Interface feels dated and resource-heavy
• Limited features in the free version compared to ReadyAPI
• Steeper learning curve for advanced scenarios

7. REST-assured

REST-assured is a Java-based library for REST API testing. It provides a domain-specific language that makes tests more readable and easier to write for Java developers.

It integrates seamlessly with testing frameworks like JUnit or TestNG, allowing developers to write automated API tests directly in code. It supports JSON and XML, authentication, cookies, and logging, making it a comprehensive library for REST API testing in Java projects.

Key Features:

• Fluent DSL for API testing
• JSON and XML support
• Integration with JUnit and TestNG
• Authentication and parameter support
• Logging and filtering options

Pros:

• Open-source and widely used in Java environments
• Highly readable and expressive syntax
• Eliminates boilerplate for API testing

Cons:

• Limited to Java environments
• Requires coding knowledge
• Not suitable for non-developers

8. Karate DSL

Karate DSL is an open-source framework that combines API, performance, and even UI testing in one tool. It uses a Gherkin-style syntax, allowing testers to define API tests in plain text without writing code.

It includes JSON and XML handling, parallel execution, and built-in reporting. Karate also supports API mocking and can integrate simple UI automation, making it a versatile tool for QA teams.

Key Features:

• Gherkin-based syntax
• JSON/XML assertions built-in
• Parallel execution
• API mocking and simple UI tests
• Automatic HTML reports

Pros:

• Simple, code-free test writing
• Supports multiple test types in one framework
• Runs tests in parallel for efficiency

Cons:

• Requires learning a custom DSL
• UI testing features are limited
• Java-based setup required

9. Airborne

Airborne is a Ruby-based testing framework built on RSpec, designed for REST API testing. It is lightweight and text-based, offering no GUI.

It simplifies API assertions through built-in matchers for status codes, JSON bodies, and response structures. Airborne is ideal for teams already working with Ruby and RSpec.

Key Features:

• RSpec integration
• Simple syntax for HTTP methods and assertions
• Automatic JSON parsing
• Lightweight and Ruby-based
  

Pros:

• Easy for Ruby developers
• Open-source and flexible
• Concise tests using RSpec matchers

Cons:

• Limited to Ruby environments
• Small community and limited documentation
• No GUI or visualization features

10. Apigee

Apigee, by Google Cloud, is a full API management and testing platform designed for enterprises. It provides tools for designing, monitoring, securing, and scaling APIs.

Apigee supports REST, SOAP, GraphQL, and gRPC APIs. It also includes developer portals, analytics, and load testing features, making it more than just a testing tool – it’s a comprehensive solution for managing APIs as products.

Key Features:

• API proxy and traffic management
• Multi-protocol support
• Supports Node.js
• Developer portals for API documentation
• Built-in analytics and monitoring
• Load and performance testing tools

Pros:

• Enterprise-grade management and analytics
• Strong integration with Google Cloud
• Scalable and secure solution

Cons:

• Paid enterprise platform
• Overkill for small projects
• Requires setup and maintenance

Conclusion

API is a bigger umbrella, and REST API is a unique type of API prevalent among cloud applications. REST APIs are all about communication. You have your Web App or Web Page communicate with a Cloud-Based Server via a REST API. But new developers find REST API difficult because it fails to maintain the state within sessions. This article introduced you to REST APIs, their need, and their importance. The article later took you through the 10 Best REST Clients that you can consider for API Testing.

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