What is a REST API Tool? Complete Guide for 2025
Rohit Rajpal
Explore the 5 best REST API tools in 2025, including Requestly, Postman, Apache JMeter, Karate DSL, and Rest Assured, with key features, pros, and cons.
Testing REST APIs is a critical part of software quality assurance. A REST API tool helps testers verify that APIs behave as expected under different conditions. It enables functional testing, performance monitoring, and error detection, providing detailed insights into API behavior.
REST API tools also support automation, allowing repetitive tests to run consistently across environments. They help teams catch issues early, reduce manual effort, and maintain stable application performance.
This article explores the top REST API tools in 2025 and how they help testers verify, monitor, and automate API workflows.
What is a REST API Tool?
A REST API tool is software designed to test and interact with RESTful APIs. These tools help testers send requests, examine responses, and validate that APIs behave according to specifications. They go beyond simple manual checks by enabling automation, detailed reporting, and scenario simulation.
REST API tools are used throughout the development and testing lifecycle. They allow teams to catch functional errors, identify performance bottlenecks, and verify that APIs meet security and reliability standards. These tools are valuable for both developers building APIs and testers ensuring quality.
Below are the key capabilities that define a REST API tool:
- Request and response handling: Supports sending HTTP methods such as GET, POST, PUT, and DELETE, and inspecting returned data, headers, and status codes.
- Test automation: Allows creation of reusable test scripts and integration into CI/CD pipelines for continuous validation.
- Scenario simulation: Enables testing complex workflows, chained requests, and edge cases to replicate real-world usage.
- Reporting and analytics: Provides logs, metrics, and dashboards to track test results, performance, and errors over time.
Benefits of Using REST API Tools
REST API tools help teams identify issues early, reduce manual effort, and maintain consistent quality across different environments.
Below are the main benefits of using a REST API tool:
- Improved accuracy: Detects errors in request handling, response structure, and data validation that manual testing may miss.
- Time efficiency: Automates repetitive tests, enabling faster validation of APIs across multiple environments.
- Enhanced performance insight: Measures response times, throughput, and system behavior under varying loads to identify bottlenecks.
- Consistency across environments: Ensures tests run uniformly across development, staging, and production environments.
- Support for complex workflows: Handles chained requests, parameterized inputs, and scenario-based testing for comprehensive coverage.
How Do REST API Tools Work?
REST API tools operate by sending structured HTTP requests to API endpoints, receiving responses, and processing the data for validation and analysis. They interact with the API protocol layer, manage data formats, and handle network communication.
Here is an overview of how REST API tools function internally:
- Request generation: The tool constructs an HTTP request by assembling the URL, HTTP method (GET, POST, PUT, DELETE), headers, query parameters, and body content. Internally, it formats these elements according to the HTTP protocol and encoding standards.
- Network communication: The tool opens a network connection to the server and transmits the request. It handles connection setup, SSL/TLS encryption if required, and timeout management.
- Response parsing: Once the server responds, the tool receives raw data over the network and parses it. This includes decoding JSON, XML, or other payload formats, interpreting status codes, and extracting headers for further evaluation.
- Assertion evaluation: The tool compares the received response against expected values or rules defined in the test. It performs internal checks on structure, data types, value ranges, and error codes.
- Scripting engine: Advanced tools use an internal scripting engine to execute custom logic, variable handling, loops, and conditional operations. This allows complex test scenarios without manual intervention.
- Logging and reporting: The tool records raw requests, responses, and test outcomes in logs or dashboards. Internally, it organizes data for analysis, trend identification, and historical comparison.
Choosing the Right REST API Tool
Selecting the right REST API tool requires understanding the specific needs of the project and the capabilities of the tools available.
Below are the key factors to consider when choosing a REST API tool:
- Supported protocols and methods: Verify that the tool fully supports HTTP methods (GET, POST, PUT, DELETE, PATCH) and content types such as JSON, XML, or form-data. Compatibility with authentication schemes like OAuth, JWT, or API keys is also essential.
- Automation and scripting capabilities: Evaluate whether the tool allows creation of reusable test scripts, supports variables, assertions, and can be integrated into CI/CD pipelines for automated testing.
- Performance testing support: Determine if the tool can simulate load, measure response times, and identify bottlenecks when multiple requests are sent concurrently.
- Reporting and analytics: Check if the tool generates structured reports, logs requests and responses, and provides metrics for trend analysis and debugging.
- Integration with existing workflows: Consider whether the tool works with version control, bug tracking systems, and build pipelines to fit seamlessly into the team’s process.
- Usability and learning curve: Assess whether the interface and documentation allow testers to quickly become productive while still supporting advanced features for experienced users.
Top REST API Tools in 2025
The following tools offer a mix of request handling, automation, and scenario simulation for testers. We compared these REST API tools based on key capabilities, ease of use, and suitability for different testing scenarios.
1. Requestly by BrowserStack
Requestly is an open-source REST API tool designed for testers and developers who need precision and flexibility in API testing. It provides a combination of API client functionality, HTTP interception, and request/response modification. This makes it suitable for both functional and integration testing, as well as for debugging and simulating complex API behaviors.
Key Features of Requestly:
- API Client: Quickly validate endpoints by sending structured requests with headers, query parameters, and body data.
- HTTP Interceptor: Capture live traffic from an application to identify unexpected request patterns or server errors.
- Modify Request Body: Alter payloads on the fly to test how APIs handle invalid, missing, or boundary data.
- Modify API Response: Simulate different server responses, including errors or delayed data.
- Create Mock Endpoints: Build temporary endpoints to replace unfinished or unavailable backend services.
- Cross Device Testing: Verify that APIs return consistent data and behave predictably across multiple devices, operating systems, or browsers.
Benefits of Using Requestly
Requestly empowers testers to focus on real-world API validation and scenario testing. Unlike tools that only send requests, it allows manipulation and simulation that reveal hidden issues. Key benefits include:
- Early testing without backend: Continue validating frontend behavior and integrations even when backend services are incomplete.
- Faster identification of defects: Real-time request/response modification helps quickly isolate and reproduce bugs.
Broader scenario coverage: Test edge cases, error conditions, and uncommon workflows that are hard to trigger in production. - Reliable cross-environment behavior: Ensures consistency across devices and environments, reducing post-deployment surprises.
- Team collaboration and repeatability: Share rules, mocks, and configurations across teams to ensure reproducibility of tests and faster onboarding.
Pricing
- Free: $0
- Lite: $8/month
- Basic: $15/month
- Professional: $23/month
2. Postman
Postman is a widely used REST API tool for designing, testing, and automating APIs. It provides a rich interface for building requests, organizing tests into collections, and running automated test suites. Postman supports both simple request validation and complex scenario testing with variables, environments, and scripts.
Key features of Postman
- Compose HTTP requests with headers, body, and query parameters to test API endpoints.
- Organize APIs and tests into collections, and share them within teams for collaboration.
- Add scripts to automate request setup, validate responses, and perform assertions.
- Configure multiple environments to run tests under different settings.
Pros and Cons of Postman:
Pros | Cons |
Intuitive interface for both beginners and advanced testers | Can become resource-heavy with large collections or many automated tests |
Strong scripting and automation support for complex scenarios | Limited control over low-level request interception compared to tools like Requestly |
Extensive community support and integrations with CI/CD tools | Mocking capabilities are less flexible for dynamic response modifications |
3. Apache JMeter
Apache JMeter is an open-source testing tool designed for evaluating APIs, web applications, and other services. It allows testers to perform functional testing as well as simulate load and performance scenarios. JMeter supports REST and SOAP APIs, providing options to measure response times, validate data, and analyze system behavior under different conditions.
Key features of Apache JMeter
- Send HTTP requests with different methods, headers, and payload types for functional testing.
- Create test plans to simulate multiple concurrent users and evaluate API performance under load.
- Visualize results using listeners, dashboards, and charts for response times, throughput, and error rates.
- Apply assertions to validate response status codes, data structures, and content.
Pros and Cons of Apache JMeter
Pros | Cons |
Strong performance and load testing capabilities | Interface can be complex for beginners |
Supports multiple protocols beyond REST | Setup and configuration require more effort than lightweight tools |
Detailed reporting and visualization options | Limited built-in support for real-time request/response modification |
4. Karate DSL
Karate DSL is an open-source framework for API testing that combines API test automation, performance testing, and mocks in a single tool. It allows testers to write readable test scenarios using a domain-specific language while supporting data-driven testing and integration with CI/CD pipelines.
Key features of Karate DSL
- Write API tests using a concise, human-readable syntax that combines requests, assertions, and test flow in a single script.
- Support for REST, SOAP, and GraphQL APIs, including parameterized requests and data-driven tests.
- Ability to mock API endpoints to simulate backend services during development or testing.
- Built-in support for validating JSON and XML responses with expressive assertions.
Pros and Cons of Karate DSL
Pros | Cons |
Combines API testing, mocks, and performance testing in one tool | Requires learning the Karate DSL syntax |
Supports multiple API types including REST, SOAP, and GraphQL | Limited IDE support compared to mainstream tools |
Parallel execution improves test efficiency | Smaller community compared to Postman or JMeter |
5. Rest Assured
Rest Assured is a Java-based library for testing RESTful APIs. It is commonly used in automation frameworks to write integration and functional tests directly in code. Rest Assured is suitable for testers comfortable with Java, providing precise control over requests, responses, and assertions.
Key features of Rest Assured
- Create HTTP requests and validate responses using Java syntax and fluent APIs.
- Built-in support for parsing and validating JSON and XML responses.
- Ability to integrate with testing frameworks like JUnit and TestNG for automation.
- Support for authentication methods including OAuth, Basic Auth, and API keys.
Pros and Cons of Rest Assured
Pros | Cons |
Provides precise control and detailed validation for automated API tests | Requires knowledge of Java |
Integrates seamlessly with popular Java test frameworks | No GUI; tests are written in code only |
Supports complex request/response handling and authentication | Steeper learning curve for beginners or non-developers |
Conclusion
A REST API tool helps testers validate API functionality, monitor performance, and automate testing across multiple environments. These tools provide control over requests and responses, enable scenario simulation, and improve test accuracy and coverage.
Requestly allows testers to dynamically modify requests and responses, create mock endpoints, and simulate edge cases without relying on backend availability. It supports cross-device testing and collaboration, making it a practical choice for teams that need flexibility and control in API validation.
Written by
Rohit Rajpal
Rohit Rajpal is a B2B Content Strategist at BrowserStack, helping SaaS brands build AI-first strategies that drive authority and revenue. He writes about content, strategy, and the future of search in the zero-click era.
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