Most of the applications you use these days follow the Client-Server Architecture. The Application itself is considered the Client or the Front-End part, and it needs to talk to a Server or the Back-End to load or pull the data. This communication is established with the help of HTTP protocol, yes, the same protocol that powers our Web. The Client can directly call the HTTP Services exposed on a Server by sending HTTP requests. This is where REST APIs come into the picture. REST is basically a convention for building these HTTP services. A REST Client can help you retrieve information from a system.

REST APIs define a set of constraints on how the architecture of a distributed system should behave. REST Clients facilitate communication between different online services. This article discusses the 10 Best REST API Clients and Testing Tools.

The 10 best REST API Clients and Testing Tools are listed below:

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What is REST API?

An Application Programming Interface (API) establishes a connection between computers or between computer programs (applications) by providing readily available codes and information pipelines. It is a type of software interface that acts as a mediator among other pieces of software to streamline the interaction with one another. Owing to diverse application architectures, different types of APIs (such as Program, Local, Web, or REST API) assist developers in building robust digital solutions.

Representational State Transfer, also known as REST, is basically a standardized Software Architecture Style, or in simple words, a specific type of API used by the industry to establish a connection between Client and Server. REST API is built to guide the development and design of the World Wide Web’s architecture.

REST APIs provide a flexible, lightweight way of integrating computer applications. REST APIs are a simple and standardized approach to communication, which means you don’t have to worry about how to format your data, it’s all standardized and industry use. REST APIs are scalable as well, which means as your service scales, you don’t have to worry about the growing complexity. You can easily make modifications to your data and keep track of that across Clients and Servers. They support caching which ensures high performance in large part.

Importance of REST API

REST Client: REST APIs | Hevo Data
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REST APIs provide a way of accessing web services in a flexible way without massive processing capabilities. Below are the features that highlight the importance of REST API:

  • Distinct Client and Server: The REST architecture totally separates the user interface from the Client and the Server improving the portability of the interface to other platforms. It increases the scalability of the projects allowing modifications to data as well. This also makes sure that the Client and Server evolve independently.
  • Scalability: As discussed, the decoupling of the Client and Server allows each development team to scale them easily. You can easily make changes in the database and keep track of that across the components.
  • Cacheability: A REST API should be designed to encourage the storage of cacheable data. Whenever possible, resources should be Cacheable on the Server or Client-side. Caching ensures high performance in large part.
  • Ease of Understanding: REST uses HTTP verbs (GET, POST, PUT, or DELETE) procedures for communication, and these methods are easy to understand and self-explanatory in nature. In addition, users don’t need to know method names in a specific order. REST architecture also helps to increase Developers’ productivity by allowing them to display the information on the Client-side and store or manipulate the data on the Server-side.

10 Best REST Clients and Testing Tools

Even though RESTful web services are scalable and easy to maintain web services, it is important to make use of REST Clients for advanced testing. Due to the complications in manual API testing, it is not usually the best-suited method. Hence, you need to opt for some REST Clients for testing REST APIs. Below is a comprehensive list of the 10 Best REST Clients that you can consider for API testing.


REST Client: HTTPie Logo | Hevo Data
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HTTPie is a command-line HTTP tool written in Python that you can use to test your REST APIs. HTTPie is developed for effortless testing and debugging of REST APIs and it also ensures human-friendly interaction with HTTP Servers, RESTful APIs, and Web Services. It doesn’t take much for one to get started, HTTPie uses simple and natural syntax.

Its interactive User Interface has many intuitive features like syntax highlighting, wget-like downloads, and Plugins that make REST APIs testing seamless. The built-in JSON support comes in handy for sending JSON requests. Some of its key features are:

  • User-friendly.
  • Simple and natural syntax.
  • Built-in JSON support.
  • Syntax Highlighting.
  • Colorized output.

Postman REST Client

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Postman is a scalable API testing environment that allows you to test, debug, run requests, create automated tests, document, and monitor API. With Postman REST Client, you can create and send HTTP requests to a Development Server. 

Postman’s built-in tools make it easy for developers to test API services. Postman also offers an app with the same functionalities. Some of its key features are:

  • Seamless automated testing.
  • Collaboration features for effortless sharing and management.
  • Supports Swagger and RAML (RESTful API Modeling Language) formats.
  • Offers powerful visualization compatibility.
  • Supports multiple protocols, manages cookies, and manages certificates.


REST Client: Curl
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Curl is an open-source command-line tool for transferring data to and from a Server. It’s a great tool for testing REST APIs, and you can easily create and send HTTP requests to a Development Server. You can send HTTP requests like POST, PUT, and DELETE using the cURL command. 

You can use Curl REST Client to test the basic functionalities of your REST APIs. You can either use curl from a command prompt or Cygwin package installation. Some of its key features are:

  • Allows you to send an application that is dependent upon HTTP.
  • Build a script with batch requests and execute them.
  • Supports different protocols like HTTP, FTP, IMAP, SMTP, and POP3.


REST Client: Swagger Logo | Hevo Data
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Swagger is an open-source tool that will assist you through the entire lifecycle of an API. It is developed for API design, development, and testing of API. Swagger Open API Specification creates sophisticated and auto-generated documentation and shares your REST API specification. Swagger provides a standard format to create definitions of REST APIs. Some of its key features are:

  • Supports API design, development, documentation, and testing.
  • Swagger provides many open-source tools for OpenAPI Specification.
  • Supports API mocking and virtualizations along with governance and monitoring.

Katalon Studio

REST Client: Katalon Logo | Hevo Data
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Katalon Studio is an automation tool that helps you automate your web, API, desktop, and mobile testing. It’s a free API testing platform for creating and sending HTTP requests to a Development Server. It includes all frameworks, ALM integrations, and plugins in one package. Some of its key features are:

  • User-friendly UI for creating and managing your test.
  • Free API testing platform.
  • Requires no prior programming experience.
  • Supports all types of REST and SOAP requests.


REST Client: SoapUI logo | Hevo Data
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SoapUI is an open-source tool built specifically for API testing. With SoapUI you can test REST and SOAP APIs with ease. Some of its key features are:

  • Drag and Drop functionality ensures scriptless functional testing.
  • Supports reusable scripts for load tests and security scans.
  • Supports different types of REST, SOAP, JMS, and IoT requests.
  • Supports seamless integration with 13 API management platforms.


REST Client: REST-assured Logo | Hevo Data
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REST-assured is a popular Open-Source REST Client for testing API in Java. For Java developers, it’s a preferred way to test REST services easily and automatically. Some of its key features are:

  • Allows you to write tests in clear and descriptive language.
  • Supports different types of XML and JSON requests.
  • Allows seamless integration with the Serenity Automation Framework.

Karate DSL

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Karate is an open-source API testing framework based on the cucumber library. It allows a tester to write meaningful tests in a domain-specific language for testing web services. Some of its key features are:

  • Requires no prior programming experience.
  • It supports multithreaded parallel execution.
  • Allows testing and reports generation just like any standard Java Project.


Airborne is an open-source API automation tool used for testing REST APIs. It is a Ruby-based RSpec-driven framework. It doesn’t have a UI and provides the text file to write the code. Some of its key features are:

  • Supports APIs written in Rails.
  • It can work with Rack applications.
  • To use this tool, you just need to know the fundamentals of Ruby and RSpec.


REST Client: Apigee Logo | Hevo Data
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Apigee is a cross-cloud API testing platform for measuring and testing API performance. Apigee helps organizations create unified digital experiences for both older back-end services and fully serverless stacks. It offers security and governance policies for all APIs. Some of its key features are:

  • Customizable Developer Portal.
  • Supports Node.js.
  • Open API Specification allows easy creation of API proxies.
  • Allows you to design, monitor, analyze, and scale APIs.


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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Do you use a REST Client for API testing? Share your experience of working with REST Clients in the comments section below.

Raj Verma
Business Analyst, Hevo Data

Raj is a skilled data analyst with a strong passion for data analysis and architecture, having a flair for writing technical content as well. With extensive experience in handling marketing data, Raj has adeptly navigated abstract business problems to derive actionable insights that drive significant results.

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