How to Choose a REST API Testing Tool

Today, almost every application - whether it’s a mobile app, a web service, or even smart devices - relies on APIs to share data and functionality with other systems.

Testing REST APIs is crucial because it helps to ensure that the software interacts correctly, verifies that the API produces accurate results, and handles different inputs. It also helps to check performance and identify security issues. 

There is a wide range of API testing tools, so comparing them is important to find the one that best matches a team’s needs. The right choice can speed up testing, improve accuracy, and make automation easier, resulting in more reliable APIs and higher-quality software.

In this article, we'll take a look at some of the most widely used REST API testing tools, their main features, review their strengths and weaknesses, and share tips from personal experience to help you pick the most suitable one for your team.

What is an API?

API stands for Application Programming Interface, and it defines how separate pieces of software can interact through well-specified commands and responses. It enables different applications or services to work together.

A REST API is an API built using the REST architectural style - a software design style that sets guidelines for how an API should operate.

It uses HTTP methods like GET, POST, PUT, DELETE, PATCH, etc. 

Key considerations for choosing a REST API testing tool

When choosing a REST API testing tool, consider how easy it is to use, whether it offers test automation and CI/CD integration, which protocols and standards it supports - a good REST API testing tool should handle standard HTTP methods and common data formats like JSON and XML. Support for authentication methods is also essential for testing secure APIs. Clear reporting, debugging features, cost, and strong documentation or community support are also important. 

Keeping these factors in mind helps teams pick a tool that makes API testing faster, more reliable, and easier to manage.

Types of REST API testing tools

REST API testing tools can be sorted into different types depending on how they’re used and what they focus on.

Manual and automated tools

Manual tools are good for quick checks, exploratory testing, or learning a new API. This approach is useful for identifying issues early, understanding how the API works, and validating specific scenarios before setting up automated tests.

Automated testing tools let you create scripts to run tests repeatedly, often integrating with CI/CD pipelines. They are ideal for regression testing, performance testing, and continuous integration, saving time and ensuring consistency across test runs.

Open-source and commercial tools

Open source tools are free to use and highly flexible. They allow customization and are often supported by active communities. The downside is that they may have limited official support, fewer advanced features, and may require more technical expertise to use effectively.

Commercial tools could be divided into two categories:

• Free commercial tools: They offer a mix of functionality and user-friendly features. They are easier to set up and use than most open-source tools and often include basic reporting and automation capabilities. However, some advanced features or team collaboration options may be limited to the paid versions.
• Paid commercial tools: Full-featured commercial tools come with licensing costs but provide advanced functionality, professional support, enhanced reporting, and team collaboration features.

API tool reviews

If you’re still struggling to make your choice, don’t worry - we have you covered. We’ve compiled a list of the most commonly used REST API testing tools, listing their key features and additional details, as well as best use cases, that will help you decide, or at least, narrow it down.

Postman

Postman is a widely used API testing tool that helps to interact with APIs in a simple way. You can send requests, check the responses, and automate tests without writing much code. 

Key features

• User-friendly
• Easy to use 
• Scripting-based assertion system with ready-to-use snippets
• Team collaboration
• Supports HTTP methods

Pros

• Quick and easy to learn
• Uses collections and environments to define a structure for organizing API requests 
• Supports also GraphQL, gRPC, and SOAP
• Requests can be sent manually or automatically
• Large and active community

Cons

• Advanced features require a paid plan
• Limitations in the free version
• Can be resource-consuming when handling large collections or many requests
• Has limitations if not registered

Best use cases

Postman is great for testing and exploring APIs quickly. It is good for sending requests manually, checking responses, organizing tests, and automating repeated tasks. Teams can also use it to collaborate and share setups.

Katalon Studio

Katalon Studio is a test tool for testing web, mobile, desktop, and APIs. The tool offers clear organisation of test cases and integrated assertions, and it’s balanced between ease of use and advanced options like scripting.

Key features

• User-friendly interface
• Low-code and scriptable 
• Built-in and custom keywords
• Wide variety of integrations (including CI/CD)
• Supports HTTP methods

Pros

• Supports web, mobile, and desktop testing
• Uses test suites, collections, and profiles to define a structure
• Supports also SOAP, GraphQL

Cons

• Requires registration even for a free version
• Advanced features require a paid plan
• If only the API testing is needed, then the tool may feel too complex
• May impact the performance with large test suites or parallel testing

Best use cases

Katalon Studio is a good choice for automated API testing, also when combined with web, mobile, or desktop testing. It’s useful for teams managing projects that require multiple types of tests.

SoapUI

SoapUI is a free and open source testing tool. It comes with features that simplify API testing, including scriptless functional testing, security checks, and load testing. It also supports API mocking and multiple protocols, making it a flexible option for different testing needs. It also offers a paid version called ReadyAPI.

Key features

• Scriptless functional testing
• API mocking
• Built-in assertions
• Load testing
• Supports HTTP methods

Pros

• Free and open source
• Multi-environment support
• Supports also SOAP, GraphQL, and JMS
• It is possible to create and run even complex scenarios with drag-and-drop actions

Cons

• Less intuitive for beginners
• Learning curve for advanced features
• Free versions have limitations compared to the paid version

Best use cases

SoapUI is a great fit when projects need functional, security, or performance checks in one place. It works well in more technical setups where scripting and detailed configuration may be important. Its mocking and data-driven features also make it helpful early in development when the real API might not be ready yet.

Practical usage of tools

To see the tools in real action, I created a quick end-to-end test, which shows how easy and practical the tool may be.

Testing conditions

The same conditions (device, website, requests) were used in all tests. I went through all the CRUD cycle (Create, Read, Update, Delete). 

I used the Mockoon website. When testing an API, it is important to understand what data is required to send and what you should expect in response. On the Mockoon website, there is information about every request. Also note that not all the necessary information may be well documented.

From available resources, I used fake movies JSON data. From the documentation, we can see that the API base URL is https://playground.mockoon.com, and to access data, we have to add the resource name. In my case, the resource name is /movies. No authorization is required.

Below we have the fake movies JSON data, including title, genre, director, release year, rating, etc.

{
  "id": "c476c2ce-f138-459d-9b7f-00781e550460",
  "title": "necessitatibus brevis vicissitudo",
  "genre": "vulgus",
  "director": "Stewart Kiehn",
  "releaseYear": 1954,
  "rating": 7,
  "isPopular": false
}

{
  "title": "Sending an API",
  "genre": "action",
  "director": "API Lover",
  "releaseYear": 2025,
  "rating": 9,
  "isPopular": true
}

Testing results

Here you can take a look at the results of the created end-to-end test run with every tool.

Postman test run

Katalon Studio test run

SoapUI test run

How to choose a tool

These are only three of many available tools used for REST API testing, and the choice of the tool may vary between project needs and team skills. In short:

1. Postman is a good starting point for beginners to get familiar with API testing tools and to execute fast API tests.
2. Katalon Studio has more features, and with Katalon Studio, you can combine multiple application types in one project. It’s user-friendly and may be suitable for users with different API testing experiences.
3. SoapUI can take more time to master, but it is a powerful tool with advanced features more ideal for complex REST scenarios.

REST API testing tool usage comparison table

Common challenges in REST API testing

Testing REST APIs can be tricky because they connect different parts of a system and handle a wide range of inputs and responses. As a result, testers may face challenges related to data handling, integration, and reliability. Recognizing these challenges early helps ensure smoother testing.

Documentation and communication

When API documentation is missing, unclear, or outdated, it becomes difficult to know how endpoints work, what parameters to send, or what responses to expect. This can slow down testing and lead to mistakes. 

Collaboration between developers and testers can reduce misunderstandings and incorrect decisions when creating tests.

Authentication and authorization

When testing APIs, you may require authentication (tokens, OAuth, API keys), which can make it challenging to manage secure access during testing.

Data management

API testing may require prepared data; keeping it organized across tests can be challenging. Cleaning up after each test is important to avoid leftover data affecting future runs.

Performance and load testing

REST APIs can behave differently when many users access them simultaneously or during heavy traffic. To identify slow points or bottlenecks, you need to carefully simulate these scenarios.

Error handling

APIs can respond with different error codes when requests are invalid or unexpected. Making sure tests cover all these cases can be tricky, but it is essential to ensure the API acts reliably in every scenario.

Conclusion

REST API testing is needed to ensure that applications work correctly and perform well. The right API testing tools make this process faster and easier by automating repetitive tasks, managing test data, and simulating different scenarios. Using these tools helps teams catch issues early and improve reliability.

Choosing the right tool depends on the team's needs, project complexity, and skill level. Some tools are simpler and faster to learn, while others offer advanced automation,  multi-platform testing, or advanced API validation. The key is to pick a solution that fits your workflow and allows the team to test efficiently without adding unnecessary complexity.