postman alternative open source

published on 16 December 2023

Developers would likely agree that having a robust API testing tool is critical for building quality applications.

An open source alternative to Postman offers the power and customizability of Postman without the cost or vendor lock-in, providing developers more freedom and flexibility.

In this post, we'll explore the world of open source Postman alternatives, from JavaScript-based clients like Thunder Client, to online tools like Hoppscotch, to IDE integrations with REST Client. We'll compare features, ease of use, customizability, and community support to help you find the right open source option for your API testing needs.

Introduction to API Testing Tools

Understanding the Role of API Testing Tools

API testing tools like Postman play an important role in modern software development. As more applications adopt microservices and API-driven architectures, thorough API testing is essential to ensure seamless integration between components. Tools like Postman simplify API testing by allowing developers to easily send requests, inspect responses, configure tests, mock servers, and more. This improves developer productivity and reduces defects that could arise from API issues. Overall, API testing tools lead to higher quality software.

Exploring the Popularity of Postman

Postman has emerged as the most popular API testing tool due to its intuitive interface, comprehensive feature set, and active community support. Key features like customizable collections, environments, automated test suites, mocking, documentation, and team collaboration have made Postman a favorite among developers. It also offers native apps, a Chrome extension, and integrations with popular tools and code repositories. With support for testing REST and GraphQL APIs, Postman provides a one-stop solution for comprehensive API testing needs.

The Shift to Open Source Alternatives

While Postman offers an impressive free tier, teams working on business applications may seek open source alternatives to avoid Postman usage limits or possible vendor lock-in. Options like REST Easy, OpenAPI Studio, Hoppscotch, and Swish offer similar core functionality to Postman. As they are open source and self-hosted, they provide greater control, transparency, and flexibility. Their active development communities also make them compelling low-cost Postman alternatives for developers seeking unlimited and customizable API testing capability.

What is a free alternative to Postman?

Postman is a popular tool for API testing and development, but there are several capable open source alternatives available. Here are some top options:

Katalon Studio

Katalon Studio is a comprehensive test automation platform supporting API, web, and mobile testing. Its free open source version includes a feature-rich API tester with request builders, test runners, reporting, and more.

Katalon handles things like environment and data management while integrating with CI/CD pipelines. It uses Selenium and Appium under the hood and allows switching between manual and automated testing modes. The interface is intuitive for those familiar with Postman.


Inomnia is an open source API client focused on usability and custom workflows. It offers interactive editing of requests, code generation snippets, environment variables, and theming options.

Insomnia supports REST, GraphQL, and gRPC services. It can import from Postman and Swagger/OpenAPI specs. The client features built-in authentication helpers, cookie management, and access to response history.

Swagger UI

Swagger UI visualizes OpenAPI descriptions from REST services as an interactive API explorer. It generates request forms and response data to help developers quickly test endpoints.

Although less fully-featured than Postman, Swagger UI integrates well with documentation-first design. Paired with a mock server, it provides an open source stack for API testing needs.

Is there a free version of Postman?

Yes, Postman offers a free version for individual users. The free Postman account includes access to Postman's core features such as:

  • Building and testing APIs
  • Creating collections of requests
  • Using the Postman API
  • Real-time documentation
  • Run collection runner
  • Team collaboration

The free version allows unlimited API requests per month and supports up to 1 team member.

While the free account offers plenty for individual developers and testers, Postman also provides paid plans that include additional features such as:

  • More team members
  • Additional workspaces
  • Long term data retention
  • Priority support
  • Dedicated IP addresses

So if you're looking to use Postman for personal or small project API testing, the free account should suit your needs. But for larger development teams that need features like audit trails and admin controls, Postman's paid plans provide enterprise-level support.

Overall, Postman's generous free offering makes it easy for most developers to get started with API testing and development. And if your needs grow over time, Postman provides affordable pricing tiers to upgrade as necessary.

Is Postman free and open source?

Postman started out as an open source project, with the Postman Runtime, Postman Collection Format, and SDKs released under an open source license to provide developers flexibility.

However, the main Postman application is no longer open source. The free Postman app has a usage limit of 1,000 API calls per month for free users. To remove this limit and access additional features like team collaboration requires a paid subscription plan starting at $8 per month.

So in summary:

  • The Postman Runtime, Collection Format, and SDKs are open source to customize and extend.
  • But the main Postman app is freemium rather than open source, with paid plans to unlock full functionality.

There are a few open source alternatives to Postman's GUI app to consider:

  • Insomnia: Feature-rich REST API client with collaboration features.
  • Hoppscotch: Lightweight browser-based API development ecosystem.
  • RESTEasy: Popular Java framework with GUI client.

These provide open source self-hosted options without restrictive usage limits. They can be good choices for developers who want more control, customization, and community-driven development.

Is swagger better than Postman?

Postman and Swagger serve different purposes when it comes to API development, testing, and documentation.

Postman is a GUI-based HTTP client used for API testing and development. It allows developers to quickly test APIs by sending HTTP requests and inspecting responses. Some of Postman's key capabilities relevant to API testing include:

  • User-friendly GUI for sending HTTP requests without needing to write code
  • Variables, environments and collections to easily organize and re-use requests
  • Built-in test scripts to validate responses
  • Mock servers to simulate APIs that don't exist yet

Swagger (also referred to as Open API) is a specification for defining and documenting REST APIs. It allows API developers to represent API contract and documentation in a language-agnostic format. Some of Swagger's key capabilities related to API documentation include:

  • Auto-generate interactive API documentation from Swagger definitions
  • Standard way of representing API contract that can integrate with different languages/frameworks
  • Definition of API endpoints, parameters, auth, models etc in human and machine readable format.
  • Built-in UI to immediately test APIs from the documentation

In summary:

  • Swagger is better for API documentation and design since it provides a standardized way of representing entire API contract in human and machine readable format.
  • Postman is better for API testing and development because it offers easy to use GUI, variables, mock servers etc specifically optimized for testing and development needs.
  • Postman does not offer as sophisticated load testing capabilities as dedicated load testing tools like JMeter or Gatling.
  • Swagger has some load testing features through its Swagger UI but they are also not as comprehensive as dedicated load testing tools.

In an ideal workflow, Swagger and Postman play complementary roles - Swagger for API design and docs while Postman for testing during development. Many teams use them together gain productivity boost across the API development lifecycle.

Evaluating Open Source Alternatives to Postman

Postman has become a very popular tool for API testing and development. However, there are a number of compelling open source alternatives that provide similar functionality. As the open source landscape continues to evolve, developers now have more choice in selecting a REST API client that fits their needs and budget.

Criteria for Choosing an Open Source REST API Client

When evaluating open source alternatives to Postman for API testing, some key criteria to consider include:

  • User Interface and Usability: The UI should be clean, intuitive, and easy to navigate when creating requests, viewing responses, setting up collections, etc. Good usability enables faster and more productive workflows.
  • Feature Set: At minimum, core functionality like request building, environments, global variables, mock servers, monitoring, documentation, and collaboration features should be present. Strong authentication mechanisms and testing capabilities are also ideal.
  • Community and Support: An active community denotes engaged users who can provide support via forums, Slack/Discord channels etc. Strong communities also contribute plugins, templating capabilities and drive future development.
  • Customizability and Extensibility: The ability to customize request headers, tests, pre-request scripts etc. Extensibility via plugins and add-ons enables tailoring the tool to very specific team needs.
  • Language and Platform Support: Native apps for Mac, Windows, Linux provide flexibility. First-class integration with coding languages like JavaScript, Java, C#, Python etc. enables easier adoption.
  • Pricing Model: Open source platforms that are free to use can provide significant cost savings over proprietary tools with restrictive license fees.

Understanding the Open Source Ecosystem

The open source ecosystem fosters rapid innovation between contributors across the world. Developers are able to build on existing projects, adding new capabilities via plugins, extensions, and modules. Open standards spur interoperability between tools. Transparency over roadmaps and priorities aligns teams to collaborate more effectively. Support and conversations happen out in the open, encouraging community involvement. These elements create a fertile environment for the evolution of API testing tools.

As developers share feedback and feature requests, open source projects exhibit greater responsiveness in delivering capabilities users want, not just what a closed product suite dictates. This user-driven development culture results in products like Insomnia and Hoppscotch gaining strong followings. Developers now have credible open source options to evaluate against Postman.

The Community's Voice: Postman Alternative Open Source Reddit Discussions

On Reddit threads discussing open source alternatives to Postman, some common perspectives emerge:

  • Insomnia is widely acknowledged as the most full-featured open source alternative. Its GUI, variable scopes, collection runners, authentication helpers, code generation, and mock servers provide robust capabilities.
  • Hoppscotch offers extreme ease of use with its clean and intuitive browser-based interface. Its collaborative features make it popular for early API exploration and prototyping needs.
  • REST Client - VSCode provides unparalleled integration as a Visual Studio Code extension. Its simplicity and focus make it a handy tool for developers already working within VSCode.

While individual needs vary, this community feedback highlights some excellent open source options to evaluate as Postman alternatives based on specific user requirements.


JavaScript-Based Open Source Alternatives

As developers adopt modern JavaScript frameworks for building applications, the need for robust API testing and development tools designed specifically for these tech stacks increases. Open source alternatives to Postman built using JavaScript offer integrations and compatibility advantages.

Postman Alternative Open Source JavaScript

Postman has become an extremely popular API testing tool, especially amongst developers using JavaScript. However, as a proprietary software, it lacks customizability and transparency. Open source alternatives built using JavaScript instead of Electron offer closer alignment with JavaScript-based workflows.

Some great open source Postman alternatives for JavaScript developers include:

  • RestLily - Offers a simple and clean UI for intuitive API testing. Integrates nicely into JavaScript projects and has VS Code and Chrome extensions.
  • Thunder Client - A VS Code extension for API testing that enables easy environment setup without leaving the editor. Supports workspace-specific customizations.
  • Insomnia - Featuring dynamic environments and data mocking, Insomnia helps streamline API testing workflows. The open source Core offers a lightweight yet fully-featured alternative.

These open source tools allow greater customizability of features like authentication, variables, and chaining requests to suit specific project needs. They eliminate vendor lock-in risks associated with Postman through community-driven development.

In addition to API testing tools, JavaScript developers can also leverage open source HTTP client libraries instead of proprietary products like Postman Runtime.

Some widely-used performant HTTP clients for JavaScript include:

  • Axios - Promise-based client that works in both client and server environments. Offers useful features like interceptors and concurrency.
  • Node Fetch - An implementation of the web Fetch API for Node.js for seamless integration across environments.
  • Got - Focused on simplicity and performance, Got streamlines making API calls without heavy overhead.

Relying on these community-backed HTTP clients reduces business risks associated with commercial products going defunct. They also provide greater control over customizing and expanding features to address evolving API needs.

Java-Based Open Source Alternatives

This section highlights tools and libraries available for Java developers seeking a Postman-like experience.

Postman Alternative Open Source Java

When looking for open source Postman alternatives built with Java, developers have a few solid options to consider:

REST Assured is a popular Java DSL for simplifying testing of REST services. It supports testing REST/SOAP web services and validating responses using Hamcrest matchers. Key features include:

  • Intuitive DSL for mocking HTTP requests
  • Validation of status codes, headers, cookies, body content
  • Seamless integration with testing frameworks like JUnit and TestNG

REST Assured enables developers to write concise yet flexible automated API tests. The learning curve is reasonable for those familiar with Java and JUnit. It can handle complex use cases like authentication, file uploads, etc. Overall, this open source library tackles many of the core capabilities offered by Postman.

HttpClient is another widely-used Java solution for invoking web services and validating responses. It is more low-level compared to REST Assured but quite versatile. Developers can build custom request/response logic while leveraging the connection management, authentication, and configuration offered by the library. When combined with a JSON parser like Gson or Jackson, HttpClient provides a programmatic approach to API testing without needing an external app like Postman.

For developers needing a graphical interface, Swagger Inspector is an open source alternative that includes a GUI for Import/Export of Postman collections. It can also mock endpoints and offers code generation capabilities across various languages including Java. The UI is intuitive and Postman users should feel right at home. The CLI version helps integrate Swagger Inspector into CI/CD pipelines for API testing.

So while Postman still reigns supreme for many Java developers, the open source options continue to evolve rapidly. REST Assured and HttpClient simplify raw HTTP/JSON interactions while Swagger Inspector offers a comparable GUI workflow. Ultimately, the choice comes down to the level of visual workflow versus programmatic control needed for your API testing strategy.

Discovering Alternatives on GitHub

GitHub hosts many open source projects offering viable alternatives to Postman for API testing. These projects are often actively maintained by contributors and have plenty of stars indicating community interest.

Postman Alternative Open Source GitHub Repositories

Some of the top open source Postman alternatives hosted on GitHub include:

  • Hoppscotch: A free, fast, and beautiful API development ecosystem that helps developers build APIs quicker. It has over 18K stars on GitHub.
  • Insomnia: A popular, open-source REST API client with support for GraphQL and WebSocket APIs. It has over 17K stars and offers multi-platform support.
  • RESTEasy: A fully certified and portable implementation of the JAX-RS specification. It simplifies the development process of RESTful web services in Java.
  • Swagger Inspector: An API inspection tool that allows testing and generating OpenAPI definitions from REST services. It is a part of the popular Swagger toolset.
  • Thunder Client: A VS Code extension for interacting with REST API endpoints. It offers intuitive GUI with autocomplete, variables, and test runner.

These projects check many of the boxes that Postman offers like API development features, testing capabilities, import/export, multi-platform availability etc. They are great open source alternatives to try out, especially since the code is public and customizable. Developers and testers can leverage them to improve API workflows.

Online and Browser-Based Alternatives

Online and browser-based tools provide convenient alternatives to Postman that allow quick and easy API testing without requiring desktop installation. These platforms offer similar core functionalities but in a more accessible web interface or browser extension.

Postman Alternative Online Platforms

Several online API testing platforms offer Postman-like capabilities directly within the browser. These include:

  • Hoppscotch - Open source web-based API development ecosystem that allows building, documenting, and testing REST/GraphQL/SOAP APIs. It provides ready-made collections for quick testing along with code snippets generation, mock servers, and API monitoring.
  • Restlet Client - User-friendly web app for sending HTTP requests and inspecting responses. Some key features include history tracking, code snippets, global variables support, OpenAPI imports, and team collaboration.
  • ReqBin - Enables rapid API testing and prototyping through its intuitive browser-based interface. Users can easily create requests, view responses, generate code snippets, import Postman collections, and share workspaces.
  • Guzzle - PHP HTTP client and framework for building RESTful web service clients. It handles many key API testing tasks like requests, responses, headers, authentication, streaming, and parallel requests execution.

These online tools eliminate the need for desktop installation while providing many Postman-like conveniences for API testing and development right from the browser.

Postman Alternative Chrome Extensions

For quick access within Chrome browser, Postman offers these handy extensions:

  • Restlet Client - This Chrome extension complements the Restlet Client web app by allowing requests creation, editing, sending, and inspection conveniently within Chrome's dev tools panel.
  • Postwoman - Open source alternative to Postman Chrome extension focused on smooth workflows and minimalistic design. It enables easy API exploration with dynamic parameter handling, global variables support, and history persistence.
  • HuTool - Retains Postman's core features as a lightweight Chrome extension with real-time updating and syncing between desktop app and browser extensions.

These extensions integrate API testing abilities in a browser context, facilitating rapid requests creation and analysis without switching tools.

Integration with Code Editors

Integrating API development capabilities into code editors enhances developer productivity by enabling testing right from the IDE. This section looks at some open source extensions for Visual Studio Code that serve as effective Postman alternatives.

Postman Alternative VSCode Extensions

Visual Studio Code is a hugely popular open source code editor among developers. Its extensibility enables developers to add extra functionality through extensions. Here are some useful VSCode extensions for API testing and development that can replace Postman:

  • Thunder Client - This lightweight extension lets you make HTTP requests directly inside VSCode and view responses in a neat UI. It supports features like query params, headers, OAuth2 authentication, and provides code snippets to integrate requests into project code.
  • REST Client - A simple REST client for testing HTTP/REST endpoints right from VSCode. It allows sending various HTTP verbs like GET, POST, PUT, DELETE via an easy-to-use interface and provides useful formatting for requests and responses.
  • Huachao Mao Rest Client - Builds on the REST client idea but adds extra capabilities like environments, globals, auth, etc. Supports Postman collections allowing easy import/export of existing requests.
  • API Client - Provides a GUI for inputting requests and viewing responses. Has easy environment handling and auth management. Allows exporting collections as Postman format.

These open source extensions integrate REST testing abilities into the VSCode editing workflow. They provide similar capabilities to Postman like params, headers, auth in a lightweight manner minus some advanced Postman-specific features. For developers wanting to test APIs as part of coding, these serve as handy Postman alternatives.


Final Thoughts on Choosing the Right Tool

When selecting an open source alternative to Postman for REST API testing and development, it is important to consider your specific needs and preferences. Factors like programming language support, integration with IDEs, debugging capabilities, collaboration features, and GUI vs code-based options should guide your decision.

For JavaScript developers working in Node.js, Restify may be the best fit due to its seamless integration and debugging support. Those using VSCode may prefer Thunder Client for its tight editor integration. Java developers can consider REST Assured or Spring Cloud Contract for native JVM support. For team collaboration, Swagger UI has built-in features for shared API specs. Command-line aficionados may opt for HTTPie over a GUI.

While Postman offers an unmatched breadth of features, open source alternatives provide greater customization, transparency, and control for your particular workflow. Evaluating your must-have capabilities and long-term plans can clarify the ideal choice. With robust options now available across languages and environments, developers have more flexibility than ever to find the right open source API testing tool.

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