Top 15 Free Tools for API Documentation

Good API documentation is the cornerstone of a successful API strategy. It’s the map that guides developers, enabling them to understand, integrate, and effectively utilize your APIs. Without clear, comprehensive, and accessible documentation, even the most powerful API can become a source of frustration rather than innovation.

But creating and maintaining high-quality API documentation can be challenging. Thankfully, a plethora of tools are available to streamline this process, many of them free to use. This guide will walk you through over 20 top free API documentation tools.

Why is Excellent API Documentation Crucial?

Before diving into the tools, let's quickly recap why investing in good API documentation is non-negotiable:

• Faster Developer Onboarding: Clear documentation significantly reduces the learning curve for developers, allowing them to get up and running with your API quickly.
• Reduced Support Overhead: Comprehensive docs answer common questions, freeing up your support team to handle more complex issues.
• Improved Collaboration: Documentation serves as a single source of truth, fostering better communication and collaboration between frontend, backend, and QA teams.
• Increased API Adoption: Well-documented APIs are easier to understand and integrate, leading to wider adoption and use.
• Enhanced Developer Experience: A positive documentation experience contributes significantly to overall developer satisfaction.

Key Features to Look for in an API Documentation Tool

When evaluating API documentation tools, consider these key features:

• Ease of Use: The tool should be intuitive for both documentation writers and readers.
• Automation: Features like auto-generation from API specifications (e.g., OpenAPI, Swagger) save significant time and effort.
• Interactivity: Interactive documentation (e.g., "Try it out" functionality) allows developers to test API calls directly from the docs.
• Customization: The ability to customize the look and feel to match your brand is essential.
• Collaboration: Features that support team collaboration, such as version control and commenting.
• Versioning: Support for managing multiple versions of your API documentation.
• Import/Export: Compatibility with common API specification formats and the ability to export documentation in various formats (HTML, PDF, Markdown).

Top 15 Free API Documentation Tools to Consider

Here’s a rundown of some of the best free (or with generous free tiers) API documentation tools available today:

1. Apidog — The All-in-One API Documentation Tool You Should Know

Apidog stands out as a comprehensive, collaborative platform for API design, API documentation, API automated testing, API debugging and API mocking. Unlike fragmented solutions, Apidog unifies your workflow—no more switching between Postman, Swagger, and other tools.

Key Features:

• Instant API Testing: Test endpoints in real time while documenting.
• One-Click Online Docs: Instantly publish and share interactive API documentation.
• Mock APIs: Create a mock server instantly and automatically as long as the API documentation is generated.
• Effortless Code Generation: Export ready-to-use code for various frameworks.
• Collaboration: Real-time editing and updates, version control, and team management.
• Visual Dashboard: No steep learning curve—get started fast.

Why Choose Apidog?

• Replace chaos with a single source of truth for your API specs.
• Empower every team member: designers, developers, QA, and product managers.
• Enjoy seamless integration with your existing workflows and tools.

Ready to get API documentation tool that does it all?
Sign up for Apidog for free and experience the future of API documentation.

2. Swagger UI: The Classic API Documentation Tool

Swagger UI is a free, interactive REST API documentation tool that generates a visual representation of an API from an OpenAPI (formerly Swagger) specification file. It's a popular choice because it's easy to use, automatically adapts to API changes, and provides a strong community support network. Swagger UI also facilitates testing and validation of API endpoints directly in the browser.

Key Features:

• Visual API Documentation: Swagger UI automatically creates a user-friendly, visual interface that displays all API endpoints, parameters, request/response structures, and more.
• Interactive Exploration: Developers can interact with the API directly through the UI, testing methods (GET, POST, PUT, DELETE) and viewing parameters in real-time.
• Error Detection and Correction: The tool can identify errors in the OpenAPI specification and provide suggestions for improvement.
• Automatic Updates: When the OpenAPI specification is updated, the Swagger UI documentation automatically reflects the changes, ensuring that the documentation stays current.
• Open Source and Free: Swagger UI is open source and freely available, with optional cloud-based hosting options available through Swagger Hub.

Why Choose Swagger UI?

• Ease of Use:It's designed to be simple and easy for developers of all skill levels to use.
• Efficiency:The automatic generation of documentation and interactive exploration saves time and effort during API development.
• Testing and Validation:Users can test and validate API endpoints directly in the browser, ensuring that the API behaves as expected.
• Community Benefits:The large and active community provides valuable resources, support, and opportunities for collaboration.
• Open Source and Free:The open-source nature and free availability make it accessible to a wider audience.

3. API Blueprint: A Powerful API Documentation Platform for Web APIs

API Blueprint is a simple, human-readable format for describing APIs, designed to facilitate API documentation and design, especially during the API lifecycle. It's built on Markdown, making it easy to write and understand, and it supports detailed documentation of requests, responses, and data structures using MSON (Markdown-based Schema Notation). API Blueprint can be used for API design, documentation, and even testing.

Key Features:

• Human-readable syntax: API Blueprint uses a Markdown-based syntax, making it easier to read and write than JSON-based specifications like Swagger.
• MSON for data structures: The MSON syntax allows for clear and concise definition of request and response structures, including simple and complex data types.
• Focus on API lifecycle: API Blueprint can be used for all phases of the API lifecycle, from design and prototyping to documentation and testing.
• Tools and integrations: There are various tools and integrations available for API Blueprint, including Aglio for generating HTML documentation and Drafter for converting API Blueprint to JSON.
• Collaboration-friendly: The Markdown-based syntax makes it easier for teams to collaborate on API documentation.
• Flexibility: API Blueprint can be used with different architectural styles and protocols.

Why Choose API Blueprint:

• Readability: The Markdown-based format makes it easy to understand and maintain the API documentation, even for non-technical stakeholders.
• Simplicity: The syntax is relatively straightforward, making it easy to learn and use.
• Support for API lifecycle: API Blueprint can be used throughout the API lifecycle, from design to documentation to testing.

4. apiDoc — Inline Documentation for RESTful Web APls

apiDoc is an open-source tool that generates documentation for RESTful APIs from comments embedded in your source code. It's a convenient choice for developers who prefer to document their APIs inline with their code. apiDoc offers features like versioning, customizable templates, and various output formats, and it's free to use.

Key Features:

• Inline Documentation: apiDoc generates documentation from annotations within your source code, making it easy to keep documentation up-to-date with the code.
• Easy to Use: It's relatively straightforward to set up and use, but requires familiarity with its annotation syntax.
• Customizable Templates: You can tailor the generated documentation's appearance to your specific needs.
• Various Output Formats: apiDoc can produce documentation in HTML, Markdown, and PDF formats.
• Versioning: It supports versioning, allowing you to track changes and compare different API versions.
• Open-Source and Free: apiDoc is free to use and has a relatively small, but active, user community.

Why Choose apiDoc:

• Simplicity: Its ease of use and seamless integration with codebases make it a good choice for developers who prefer to document their APIs inline.
• Documentation as Code: Keeping documentation as part of the codebase ensures that it's always up-to-date with the API.
• Automation: apiDoc automates the documentation generation process, saving developers time and effort.
• Customization: The ability to customize templates allows you to create documentation that best suits your project's style.
• Free and Open-Source: The free and open-source nature of apiDoc makes it a budget-friendly option.

5. Apiary — Interactive & Developer-Friendly API Documentation Tool

Apiary is an API documentation platform that helps teams create, manage, and maintain clear, interactive, and collaborative API documentation. Built with developers in mind, Apiary provides tools that simplify the process of designing and explaining APIs while enhancing usability, accessibility, and team productivity.

Key Features:

• Interactive Documentation: Apiary allows users to explore API endpoints, request/response parameters, and sample requests through an interactive interface, enhancing understanding and usage.
• Mock Servers: Teams can create mock servers within Apiary to define and test APIs before any code is written, saving time and effort.
• Rapid Prototyping: Apiary enables teams to validate API designs early in the development process, reducing the risk of integration issues later.
• API Blueprint and Blueprint API: Apiary offers the API Blueprint, a format for describing APIs, and a tool for building and testing APIs based on blueprints, as well as other API specifications.
• Code Generation: Apiary supports code generation for various programming languages, further streamlining the API development process.

Why Choose Apiary:

• Improved API Understanding: Apiary's interactive documentation makes it easier for developers to understand and use APIs.
• Early Validation: The ability to test APIs early in development helps identify and resolve issues before coding begins.
• Reduced Integration Risks: By validating API designs early, Apiary helps reduce the risk of integration problems later in the development cycle.
• Streamlined API Development: Apiary's features, including mock servers and code generation, can significantly streamline the API development process.

6. DapperDox — Beautiful, Integrated, OpenAPl Documentation

DapperDox is an open-source API documentation generator and server for OpenAPI specifications. It combines OpenAPI specs with rich documentation, guides, and diagrams authored in GitHub Flavoured Markdown, creating browsable reference websites for APIs.

Key Features:

• OpenAPI Integration: Seamlessly integrates with OpenAPI specifications (OAS 2.0 and OAS 3.0).
• Markdown Support: Allows users to add rich text content, descriptions, and examples in GitHub Flavored Markdown.
• Multiple OpenAPI File Support: Handles multiple OpenAPI files, enabling comprehensive API documentation.
• Enhanced Navigation: Provides user-friendly navigation and presentation of API documentation.
• Built-in API Explorer: Includes an API explorer for testing API calls directly from the documentation.
• Theme Customization: Offers multiple themes and allows for custom theming.
• Proxy Support: Can proxy developer platforms, enabling API key management integration.
• Open-Source and Free: DapperDox is an open-source project and is free to use.

Why Choose DapperDox:

• Rich and Integrated Documentation: Provides a comprehensive and visually appealing API documentation experience.
• Open-Source Nature: Benefits from a community-driven development process and avoids licensing costs.
• Markdown-Based Content: Facilitates easy authoring and editing of documentation alongside API specifications.
• API Explorer for Testing: Enables users to experiment with API endpoints directly within the documentation.
• Flexibility and Customization: Offers a variety of themes and customization options.
• Developer Platform Integration: Supports integration with developer platforms for API key management.

7. DocFX — Static Site Generator for .NET API Documentation

DocFX is a versatile documentation generator that helps developers create and manage API and conceptual documentation for .NET projects and more. It's particularly useful for generating API reference documentation from XML code comments, but it also supports Markdown and other formats, enabling the creation of static websites for various documentation needs.

Key Features:

• API Documentation Generation: DocFX automatically generates API reference documentation (including namespaces, classes, methods, etc.) from XML comments within your source code.
• Static Site Generation: It produces a static HTML website from your documentation content, making it easy to deploy and host anywhere.
• Cross-Platform Support: DocFX runs on Windows, macOS, and Linux, allowing for seamless integration into diverse development workflows.
• Customization: It offers templates and plugins for customizing the appearance and functionality of your documentation.
• Markdown Support: DocFX supports DocFX Flavored Markdown (DFM), which is compatible with GitHub Flavored Markdown (GFM) and includes useful extensions for documentation writing.
• Integration with Source Code: You can seamlessly navigate to your source code from the documentation, making it easy to find the source of API documentation.

Why Choose DocFX:

• Streamlined Documentation Process: DocFX automates the documentation generation process, saving developers time and effort.
• Versatile: DocFX supports both API and conceptual documentation, making it suitable for a wide range of projects.
• Flexibility: Supports various markup formats (e.g., JSON, YAML, Markdown) and can be extended with plugins and templates.

8. Document360 — Flexible Documentation Tool for API

Document360 provides a platform for building and managing API documentation, offering features like automatic documentation generation from API definition files, interactive documentation, and a user-friendly interface for developers and technical writers. This platform is suitable for organizations looking to create comprehensive, easy-to-use API documentation for their developers and customers.

Key Features:

• Automatic Generation: Document360 can automatically generate API documentation from OpenAPI specification files (JSON or YAML), making the process of creating documentation efficient and reducing manual effort.
• Interactive Documentation: Users can directly test API endpoints from the documentation portal using the "Try it" feature, enhancing understanding and use of the API.
• Comprehensive Coverage: The documentation covers all aspects of the API, including endpoints, parameters, response codes, and data models, ensuring a complete reference for developers.
• Customizable: Users can customize the appearance and structure of the API documentation to fit their specific needs and branding.
• Version Control: Document360 enables managing multiple versions of API documentation, allowing for tracking changes and ensuring users have access to the correct documentation for their use case.

Why Choose Document360:

• Efficiency: The automatic generation feature reduces the manual effort and time required to create API documentation, allowing teams to focus on other tasks.
• Improved Developer Experience: The interactive documentation and developer-friendly interface make it easier for developers to understand and use the API, leading to faster integration and development.
• Comprehensive Solution: Document360 provides a complete solution for API documentation, encompassing all aspects of API management and documentation.
• Cost-Effective: By automating the documentation process and improving developer efficiency, Document360 can help organizations reduce costs associated with API documentation.

9. Doxygen — Widely-used Documentation Generator Tool

Doxygen is a widely adopted open-source documentation generator that helps software developers create structured, maintainable, and comprehensive documentation directly from annotated source code. It streamlines the documentation process for projects of all sizes and supports multiple programming languages, making it a go-to tool for teams seeking consistency, automation, and clarity in their codebase documentation.

Key Features of Doxygen:

• Multiple Output Formats: Doxygen supports a wide range of output formats, including:

  • HTML – For interactive, web-based documentation
  • PDF – Via LaTeX, ideal for printable documentation
  • RTF/Word – For easy integration into word processors
  • XML – For further processing or custom tooling

• Multi-language Support: While Doxygen excels at C++ documentation, it also supports many other programming languages:

  • C, Python, PHP, Java, C#
  • Objective-C, Fortran, VHDL, IDL, and more

• Cross-referencing: Doxygen automatically builds cross-references between documented code elements. It generates hyperlinks between related classes, methods, variables, and files, enabling developers to navigate large codebases more efficiently and understand the relationships between components with ease.

• Diagrams and Visuals: Doxygen can generate class hierarchy diagrams, call graphs, and collaboration diagrams using Graphviz. These visual aids provide a high-level view of object relationships, control flow, and dependencies—valuable for both documentation consumers and maintainers.

• Customizable Configuration: Doxygen uses a configuration file (Doxyfile) that allows fine-grained control over the documentation process. Users can:

  • Choose output formats
  • Include or exclude specific files or directories
  • Control how detailed the documentation should be
  • Set up custom tags and filters

Why Choose Doxygen:

• Automates Tedious Work: Instead of writing documentation from scratch, Doxygen parses source code comments and generates structured documentation, saving time and reducing human error.
• Standardizes Documentation Across Teams: With consistent formatting and cross-references, teams can maintain a unified documentation style even across large or multi-language projects.
• Ideal for Technical Documentation Compliance: Many teams use Doxygen to meet industry standards for documentation, especially in regulated or safety-critical industries.

10. Gitbook — Tool  for Professional-Looking Product Documentation

GitBook is a platform and tool that facilitates the creation, collaboration, and publishing of documentation and books. Its key features include a user-friendly editor, real-time collaboration, integration with Git for version control, and support for Markdown syntax.

Key Features:

• User-Friendly Interface: GitBook boasts a simple and intuitive interface, making it easy to create, edit, and organize documents.
• Real-time Collaboration: Multiple users can simultaneously edit and contribute to documents within GitBook, streamlining teamwork.
• Git Integration: Seamless integration with Git allows for version control, enabling teams to track changes, revert to previous versions, and collaborate effectively.
• Markdown Support: GitBook supports Markdown syntax, simplifying the formatting of documents and ensuring consistency.

Why Choose GitBook:

• Ease of Use: GitBook's user-friendly interface makes it easy for individuals and teams to get started and produce high-quality documentation.
• Collaboration: The real-time collaboration features enhance teamwork and facilitate efficient documentation creation.
• Version Control: Git integration ensures that changes are tracked, allowing for easy reversion and collaboration.
• Professional-Looking Documentation: GitBook enables the creation of visually appealing and professionally formatted documentation.

11. OpenAPl Generator — API-first Documentation Tool

OpenAPI Generator is a powerful tool that automatically generates API client libraries, server stubs, and documentation from OpenAPI (formerly Swagger) specifications. It's designed to streamline the API development process by automating repetitive tasks and ensuring consistency across teams.

Key Features:

• Code Generation: OpenAPI Generator can generate code for various programming languages and frameworks, including Java, Python, JavaScript, and more. This reduces manual coding effort and ensures consistency in API client implementations.
• Interactive Documentation: OpenAPI Generator can produce interactive API documentation, allowing developers to explore and understand the API without needing to examine the source code.
• API-First Approach: OpenAPI Generator supports an API-first development strategy, where the API specification is defined first, and then the client and server code are generated.

Why Choose OpenAPI Generator:

• Automation: Reduces manual effort, saves time, and minimizes errors.
• Consistency: Ensures that all parts of the system adhere to the same API specification, promoting consistency across the development lifecycle.
• Improved Collaboration: Facilitates cooperation between backend and frontend teams by providing a common contract for API interactions.
• Scalability: Makes it easier to build and maintain large-scale APIs.
• Cost-Effective: Saves time and resources by automating code generation and documentation.

12. Postman — A Comprehensive API Documentation Tool

Postman is a platform for API development, testing, and documentation. It simplifies the API lifecycle, from design to delivery, with a focus on collaboration and efficiency.

Key Features:

• Automatic Generation: Postman automatically generates documentation for collections and APIs, including details about requests, parameters, and examples.
• Interactive Documentation: Users can test API endpoints directly from the documentation.
• Collaboration: Postman facilitates team collaboration through shared workspaces and commenting features.
• Customization: Documentation can be customized with descriptions and examples.

Why Choose Postman:

• Ease of Use: Postman's user-friendly interface makes it easy to create and manage documentation.
• Comprehensive API Platform: Postman handles API design, testing, and documentation in one platform.
• Collaboration: Postman allows teams to collaborate on API documentation, ensuring accuracy and up-to-date information.
• Interactive Testing: Users can test APIs directly from the documentation, making it easier to understand and use.
• Automation: Postman automates documentation generation, saving time and effort.

13. RAML — A Documentation Tool for REST API

RAML is designed to simplify the process of documenting RESTful APIs while ensuring that documentation remains perfectly in sync with your implementation. By leveraging a rich ecosystem of open-source tools and parsers, RAML lets you generate, customize, and interact with your API documentation quickly and reliably.

Key Features:

• API Console: The API Console provides live interactive documentation that lets users try out your API in real time, making real calls. You can easily install the API Console on any site with just a few lines of JavaScript or host it yourself (requires Node.js)
• RAML to HTML: RAML to HTML is a documentation tool that outputs a single HTML page console based on a RAML definition. It's written in NodeJS and it can be executed as a command line.
• RAML2HTML for PHP: RAML 2 HTML for PHP is a simple application that makes use of multiple templates to allow you to build and customize your API Docs using RAML. Version 1 includes more advanced document capabilities including code samples, inclusion of Disqus comments, and more.

Why Choose RAML:

• Documentation Always in Sync: By defining your API contract in a single RAML file, you eliminate drift between code and docs. Any change to the RAML specification instantly propagates through all generated outputs.
• Rapid, On-the-Fly Generation: Tools like RAML to HTML and API Console enable you to publish or update docs in seconds—no manual YAML editing or rewriting of markdown files.
• Interactive Exploration: The API Console and API Notebook turn static documentation into an interactive playground, speeding up onboarding and reducing support questions.

14. ReadMe — Robust Platform for Documenting APIs

ReadMe is a platform designed to create and manage API documentation. It aims to simplify the process of creating, maintaining, and distributing API documentation, making it easier for developers to understand and use APIs.

Key Features:

• Project Overview: Briefly describes the project's purpose and functionality.
• Installation Instructions: Guides users on how to set up the project on their systems.
• Usage Instructions: Explains how to use the project, including examples and tutorials.
• Contribution Guidelines: Outlines the process for contributing to the project, including code standards, issue tracking, and pull request procedures.
• License Information: Specifies the project's license, which dictates how users can use, modify, and distribute the project.

Why Choose README:

• Documentation: Provides a central hub for all project-related information.
• Clarity: Helps users quickly understand the project and get started.
• Collaboration: Facilitates teamwork and onboarding for new contributors.

15. Redoc — Open-source Documentation Tool for API

Redoc is an open-source tool that automatically generates interactive API documentation from OpenAPI (formerly Swagger) specifications. It is known for its clean, customizable, and user-friendly interface.

Key Features:

• Automatic Generation: Redoc generates documentation directly from your OpenAPI specification, ensuring accuracy and reducing manual effort.
• Three-Panel Layout: It employs a modern three-column layout, with navigation, detailed documentation, and request/response examples.
• Customizable: Redoc allows extensive customization through configuration files, CSS, and embedding into web applications, enabling tailored appearance and functionality.
• OpenAPI Support: It fully supports OpenAPI 2.0 and 3.0 specifications, ensuring broad compatibility with various APIs.
• Interactive: The generated documentation is interactive, allowing users to explore API endpoints, parameters, and responses directly.

Why Choose Redoc:

• User-Friendly Interface: Redoc's clean, well-organized interface makes it easy for developers to understand and use API documentation.
• Time-Saving: Automatic generation saves time and effort compared to manual documentation creation.
• Customization: Extensive customization options ensure that documentation fits specific project requirements and branding.
• Open Source: It is free and open-source, making it accessible to a wide range of users.
• Interactive Exploration: The interactive nature of Redoc allows users to explore APIs easily, improving the overall developer experience.

Conclusion: Elevate Your API Strategy with the Right Tools

Choosing the right API documentation tool is crucial for maximizing the value and usability of your APIs. The free tools listed in this guide offer a great starting point for projects of all sizes.

However, if you're looking for a solution that not only handles documentation superbly but also streamlines your entire API development workflow, Apidog is an unparalleled choice. Its design-first approach, comprehensive feature set, and focus on collaboration make it a powerful ally in building, documenting, and managing successful APIs.

Explore these tools, find what works best for your team, and start creating API documentation that empowers developers and drives API adoption.