• 10 Best API Testing Tools in 2021 (Detailed Review)

    API Testing ToolsTop 10 API Testing Tools for 2021 (Details & Updates Done for You!)

    In this article, we will see a summary of the popular API testing tools which contain both open-source and commercial solutions.

    API is an acronym and it stands for Application Programming Interface. API is a set of routines, protocols, and tools for building Software Applications. APIs define how software should interact with other software.

    API testing is a software testing type that focuses on testing APIs directly. It also involves integration testing to verify whether the API meets exceptions regarding the functionality, performance, security, and reliability of the application. The main focus while doing API testing will be on the Business logic layer of the software architecture.

    Check our detailed guide on API Testing.

    According to Google Trends, the interest in API testing has been growing steadily.

    Having the right process, tool, and solution for API automation tests are becoming more critical than ever.

    With the shift-left trend, API testing is a crucial component of a successful CI/CD deployment.

    Free API Testing Tools Comparison

    ProductKatalon StudioSoapUIPostmanTricentisApigee
    Application Under TestAPI/Web/Mobile/Desktop appsAPIAPIAPI/Web/Mobile appsAPI
    Supported PlatformWindows
    Ease of Installing and useEasy to setup & useEasy to setup & useEasy to setup & useEasy to setup. Need training to properly use the toolRequire end-points management knowledge to use


    SOAP & REST API Testing Tools Comparison

    Comparison Table API Testing Tools

    Top 10 API Test Tools (SOAP & REST API Test Tools) for 2021

    1. Katalon Studio

    Katalon Studio Automation Testing Tool

    Katalon Studio is a free test automation tool to test web applications, web services, and mobile applications.

    The main advantage of Katalon studio is its capability to combine UI and business levels (Web services/API) for different operating systems such as Windows, Linux, and Mac OS.

    Katalon Studio supports SOAP and RESTful requests with various types of commands such as GET, POST, PUT, DELETE with parameterized capability.


    • It supports both RESTful and SOAP requests with various types of commands such as GET, POST, PUT, DELETE with parameterized capability.
    • Capability to combine UI and API verification.
    • Many built-in keywords to create test cases.
    • It supports a data-driven approach.
    • Support one of the most powerful assertion library, AssertJ to create fluent assertion with BDD style.
    • It can be used for automated testing as well as exploratory testing.
    • It is suitable for both non-techies and pros through the support of Manual and Groovy Scripting modes.

    Katalon is named as one of the Gartner Peer Insights Customers’ Choices 2020 for Software Test Automation.

    It received over 600 positive reviews from users, with 4.4 out of 5 stars on Gartner. One user writes: “Good for beginners, fast-growing software with a lot of features”

    Website: Katalon Studio

    Pricing: Free – $69/license/month

    2. Postman

    Postman API Testing Tool

    Postman is a collaboration platform for API development. It is a popular API client. It allows us to design, build, share, test, and document APIs.

    Earlier postman is only a Chrome plugin. Now it extends its solution with the native versions of Windows & Mac.

    If you don’t want to code then you can choose Postman for your API testing. Check out our detailed Postman Tutorial to learn API testing.


    • It works on Windows, Linux, Mac OS, and Chrome Apps.
    • It supports CI/CD service with Newman
    • Easy-to-use REST client
    • The rich interface which makes it easy to use
    • Can be used for both automated and exploratory testing
    • It supports Swagger and RAML formats
    • There is no need to learn a new language
    • It enables users to easily share the knowledge with the team as they can package up all the requests and expected responses, then send it to their colleagues.

    Website: Postman

    Pricing: Free – $12/user/month

    3. SoapUI

    SoapUI logo

    SoapUI is an automated testing tool for SOAP and REST APIs. It acts as a headless functional testing tool dedicated to API testing.

    Using SoapUI, users can get the full source and build the preferred features besides these abilities:

    Free Package

    • Create tests easily and quickly with Point-and-click and Drag-and-drop
    • It allows load tests by reusability of test scripts.
    • It generates security scans to run against all your API tests.

    Pro Package

    • It supports data-driven testing: Data loaded from files, databases, and Excels. So that they can simulate how consumers interact with the APIs
    • It supports native CI/CD integrations, and asynchronous testing
    • Supports Endpoint Explorer dialog for users to send an exploratory request and analyze responses without creating a project.
    • Supports extended HTTP methods such as LOCK, UNLOCK, PROPFIND, COPY, PURGE.

    Website: SoapUI

    Pricing: Free – $659/year

    4. Tricentis Tosca

    Tricentis Tosca Orchestrated Service Virtualization

    Tricentis Tosca is a Continuous Testing platform that accelerates testing with a no-code, script-less approach for end-to-end test automation.


    • It comes with a free trial
    • It supports Agile and DevOps Cycle
    • Supports many arrays of protocols such as HTTP(s) JMS, SOAP, REST, Rabbit MQ, AMQP, TIBCO EMS, IBM MQ,NET TCP
    • It maximizes reuse and maintainability with model-based automation testing.
    • API tests can be used across mobile, cross-browser, packaged apps, etc.,
    • It allows you to achieve sustainable test automation
    • It reduces the regression testing time
    • Its interactive testing provides test managers to run manual testing and gather results without having to setup Tosca environments.
    • It supports web service security configuration in the API Connection Manager.
    • Users can use the signature security option to sign multiple parts of a message.
    • Testers are allowed to read and write files dynamically with a file connection in the API Engine.

    Website: Tricentis

    Pricing: Contact Sales

    5. Apigee


    Apigee is a cross-cloud API management platform, allowing users to measure and test API performance, supports, and build API using editors like Swagger.

    For five consecutive times, Google (Apigee) is recognized as a Leader in the Gartner Magic Quadrant for Full Lifecycle API Management.

    • It is powered by Javascript
    • Allows the design monitor, deploy, and scale APIs
    • Identify performance issues by tracking API traffic, response times, and error rates
    • Easily create API proxies from the Open API Specification and deploy them in the cloud
    • Cloud or on-premises (in a private cloud) and sometimes using a hybrid deployment model
    • PCI, HIPAA, SOC2, and PII for apps and APIs
    • Apigee is purpose-built for digital business, and the data-rich mobile-driven APIs and apps that power it.
    • Its full lifecycle API management platform provides the visualization tools, dashboards, and reports to help measure the data that flows across APIs in real-time.
    • It manages the process for designing, developing, publishing, deploying, versioning, governance, monitoring availability, and measuring performance.

    Starting from February 2019 with the release of version 4.19.01, Apigee gave users even more flexibility to manage their APIs with features like Open API 3.0 support, TLS security, self-healing with apigee-monit, virtual host management improvements, and more software support. The latest announced in Apr 2020 with minor bug fixes only.

    Website: Apigee

    Pricing: Contact Sales

    6. JMeter


    JMeter is an open-source tool. It is created to do load testing but is widely used for functional API testing.

    • It allows us to replay the test results
    • It allows the team to quickly create unique data (parameter values) for API tests through CSV files.
    • It can be integrated with Jenkins and users can include the API tests in CI pipelines
    • It can be used for both static and dynamic resources performance testing

    The most recent release in November 2019 is JMeter 5.2. The tool has been packed with multiple features and enhancements, improved user experience, and many bug fixes, such as new protocol, JMESPath extractor, JDBC improvements, StringtoFile, HTTP Samplers.

    Website: JMeter

    Pricing: Open source

    7. Rest-Assured


    Rest-Assured is an open-source Java domain-specific language that makes testing the REST service more simple.

    • It supports any HTTP method but has explicit support for various types of commands such as POST, GET, PUT, DELETE, OPTIONS, PATCH, and HEAD and includes specifying and validating e.g. parameters, headers, cookies and body easily.
    • Users don’t necessarily need to code from scratch.
    • It integrates with the Serenity automation framework
    • It generates beautiful reports
    • It supports BDD Given/When/Then syntax
    • Users don’t necessarily need to be an expert of HTTP

    Starting from version 4.0.0, Rest-Assured requires at least Java 8, instead of Java 6 as was previously required. This version also supported Apache Johnzon and fixed bunches of issues with the initial OSGi support. The latest version 4.2.0 announced in January 2020 allowed a nicer experience for Kotlin developers using the spring-mock-mvc module.

    Website: Rest Assured

    Pricing: Open Source

    8. Assertible


    Assertible is an API testing tool that continuously tests web services and concentrates on automation and reliability.

    • It supports automation API tests through each step of a continuous integration and delivery pipeline.
    • It supports running API tests after deployment
    • It can be integrated with tools such as GitHub, Slack, and Zapier.
    • Support validating HTTP responses with turn-key assertions such as JSON Schema validation and JSON Path data integrity checks
    • The Sync feature allows users to update tests when their specifications change, so they are no longer have to manually update their tests after adding new parameters or changing the response of API.

    In October 2019, Assertible introduced the latest feature called Encrypted variables, which provides a new way to store tokens, passwords, and secret data fields required by tests to improve API testing security practices. Encrypted variables are not only trivial to use, but build on the cryptographically sound methodology for safe storage.

    Website: Assertible

    Pricing: Free – $100/month

    9. Karate DSL


    Karate DSL is an open-source API testing tool that helps create scenarios for API-based BDD tests in a simple way without writing step definitions. Users can kickstart the API testing quickly because the step definitions have been created by KarateDSL.

    • It is perfect for BDD tests
    • Build on top of Cucumber-JVM
    • Can run a test and generate reports like any standard Java project
    • A test can be written without any Java knowledge required
    • Supports configuration switching/staging, multi-threaded parallel execution
    • Users don’t necessarily need to be a programmer to write tests

    Starting from version 0.9.3, Karate UI is no longer part of the open-source tool’s core but a separate Maven artifact. This version included built-in support for WebSocket that is based on the async capability. The latest update Karate UI 0.9.5 in February 2020, came with web browser automation which allows users to submit a self-contained snippet of HTML as a full-fledged project — to demo or replicate issues.

    Website: Karate

    Pricing: Open Source

    10. Swagger


    Swagger is an API testing tool that allows users to start with functional, security, and performance testing right from the Open API Specifications. Swagger tooling and Ready API platform make it easy to quickly create, manage, and execute API tests in the pipeline.

    • Swagger Inspector provides capabilities to inspect API request-responses, and make sure they perform as expected
    • Import user’s API definitions to easily validate schema rules
    • Automatically generate assertions against endpoints and inject synthetic data into parameters
    • Complex load scenarios generation to test the performance of API
    • Support all types of services from REST, SOAP to GraphQL

    Open API Spec version 3.0 in March 2019, the new feature Swagger Hub Domains was introduced. With this feature, developers can take frequently used objects, path items, response, and store them in separate files to be referenced across multiple different API definitions. These re-usable Domains can be versioned, published, and shared for collaborative feedback among large teams.

    Website: Swagger

    Pricing: Open-source


    We don’t have much information about the following two tools (ACCELQ & ReadyAPI). We heard good reviews about these two tools too. 

    11. ACCELQ


    It is a codeless test automation platform for functional and API test automation.

    Website: ACCELQ

    Pricing: Free Trial Available.

    ACCELQ API professional plan starting from $70.00 per user-month (annual billing).

    12. ReadyAPI


    The ReadyAPI platform accelerates functional, security, and load testing of RESTful, SOAP, GraphQL and other web services right inside your CI/CD pipeline. With ReadyAPI platform we get four powerful tools such as API functional testing, API security testing, API performance testing, and API & Web virtualization.

    Website: ReadyAPI

    Pricing: It starts at $749/year

    13. Test Mace


    Test Mace is a new powerful cross-platform tool that helps us to work with API and create automated API tests without coding.

    Pricing: Free Version available and it starts $4/month (First month free of charge)

    Website: Test Mace

    14. Ping API

    Ping API

    Ping-API is a powerful API inspector that allows us to inspect any HTTP API call with complete request and response data.

    Pricing: Free Version available and it starts $5/month

    Website: Ping API

    15. No one-size-fits-all tools

    Sad, but true!

    We believe the above list nominates the best solution available in the market if you are planning to adopt API automation testing. However, it is almost impossible to find the ideal-one-tool from the solutions in the industry.

    Some may find the features of the commercial players (Postman, Tricentis Tosca, etc.,) are sufficient but the costs of ownership will be the show-stop factor. Open source solutions (Rest-Assured, Karate DSL, etc.,) are affordable but require skilled resources and effort to implement the right frameworks. Tools that seem to be a relative balance between cost and other factors such as Postman, Katalon Studio might have drawbacks to specific project types that need to be considered.

    No one-size-fits-all tool

    API testing established its trend in automation testing, and more tools will be developed to serve the growing demands of the software development teams. Finding the perfect tool is still tough, but we have the good news that you have way more choices than before. Carefully considering your requirements, pros, and cons of each solution — try not too ambitious at the early stage and trial the top 5 relevant candidates from the list above. With the POC for these solutions created, you will have a better knowledge of your project’s critical factors and fine-tune your shortlist. This approach gives you a good chance to identify a suitable tool for the current status and information of the next choice when your project is more mature.

    This article was last modified in January 2021 and will be regularly updated with the latest top API testing tools and their functionalities. We love to hear your feedback. Leave a comment below if you have any suggestions on API testing products!

    I would love to hear your feedback and let me know if you have other tools to record for the others’ reference.


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