If you manage to create amazing API documentation and ensure that developers have a positive experience implementing your API, they will sing the praises of your product. Continuously improving your API documentation is an investment, but it can have a huge impact. Great documentation builds trust, differentiates you from your competition, and provides marketing value.

I’ve shared some best practices for creating good API documentation in my article “The Ten Essentials for Good API Documentation.” In this article, I delve into some research studies and show how you can both improve and fine-tune different aspects of your API documentation. Some of these extras, like readability, are closer to essentials, while others are more of a nice-to-have, like personality. I hope they give you some ideas for building the best possible docs for your product.

Overview page

Whoever visits your API documentation needs to be able to decide at first glance whether it is worth exploring further. You should clearly show:


  • what your API offers (i.e., what your products do);

  • how it works;

  • how it integrates;

  • and how it scales (i.e., usage limits, pricing, support, and SLAs).

Screenshot: The homepage of Spotify's API documentation.
Spotify’s API documentation clearly states what the API does and how it works, and it provides links to guides and API references organized in categories.

An overview page targets all visitors, but it is especially helpful for decision-makers. They have to see the business value: explain to them directly why a company would want to use your API.

Developers, on the other hand, want to understand the purpose of the API and its feature set, so they tend to turn to the overview page for conceptual information. Show them the architecture of your API and the structure of your docs. Include an overview of different components and an introduction into the request-response behavior (i.e., how to integrate, how to send requests, and how to process responses). Provide information on the platforms on which the API is running (e.g., Java) and possible interactions with other platforms.

As the study “The role of conceptual knowledge in API usability” found, without conceptual knowledge, developers struggle to formulate effective queries and to evaluate the relevance or meaning of content they find. That’s why API documentation should not only include detailed examples of API use, but also thorough introductions to the concepts, standards, and ideas in an API’s data structures and functionality. The overview page can be an important component to fulfill this role.

Screenshot: Braintree's API overview page has an illustration showing how it works.
Braintree’s API overview page provides a clear overview of their SDKs, along with a visual step-by-step explanation of how their API works.

Examples

For some developers, examples play a more important role in getting started with an API than the explanations of calls and parameters.

A recent study, “Application Programming Interface Documentation—What Do Software Developers Want?,” explored how software developers interact with API documentation: what their goals are, how they learn, where they look for information, and how they judge the quality of API docs.

The role of examples

The study found that after conducting an initial overview of what the API does and how it works, developers approach learning about the API in two distinct ways: some follow a top-down approach, where they try to build a thorough understanding of the API before starting to implement specific use cases, while others prefer to follow a bottom-up approach, where they start coding right away.

This latter group has a code-oriented learning strategy; they start learning by trying and extending code examples. Getting into an API is most often connected with a specific task. They look for an example that has the potential of serving as a basis to solve their problem, but once they’ve found the solution they were looking for, they usually stop learning.

Examples are essential for code-oriented learners, but all developers benefit from them. The study showed that developers often trust examples more than documentation, because if they work, they can’t be outdated or wrong. Developers often struggle with finding out where to start and how to begin with a new API—examples can become good entry points in this case. Many developers can grasp information more easily from code than text, and they can re-use code in examples for their own implementation. Examples also play other roles that are far from obvious: they automatically convey information about dependencies and prerequisites, they help identify relevant sections in the documentation when developers are scanning the page, and they intuitively show developers how code that uses the API should look.

Improve your examples

Because examples are such a crucial component in API documentation, better examples mean better docs.

To ensure the quality of your examples, they should be complete, be programmed professionally, and work correctly. Because examples convey so much more than the actual use case, make sure to follow the style guidelines of the respective community and show best-practice approaches. Add brief, informative explanations; although examples can be self-explanatory, comments included with sample code help comprehension.

Add concrete, real-life examples whenever you can. If you don’t have real examples, make sure they at least look real: use realistic variable names and functions instead of abstract ones.

When including examples, you have a variety of formats and approaches to choose from: auto-generated examples, sample applications, client libraries, and examples in multiple languages.

Auto-generated examples

Autodoc tools like Swagger Codegen and API Blueprint automatically generate documentation from your source code and keep it up-to-date as the code changes. Use them to generate reference libraries and sample code snippets, but be aware that what you produce this way is only skeleton—not fleshed out—documentation. You will still have to add explanations, conceptual information, quick-start guides, and tutorials, and you should still pay attention to other aspects like UX and good-quality copy.

On the Readme blog, they explore autodoc tools and their limitations in more depth through a couple of real-world examples.

Sample applications

Working applications that use the API are a great way to show how everything works together and how the API integrates with different platforms and technologies. They are different than sample code snippets, because they are stand-alone solutions that show the big picture. As such, they are helpful to developers who would like to see how a full implementation works and to have an overall understanding of how everything in the API ties together. On the other hand, they are real products that showcase the services and quality of your API to decision makers. Apple’s iOS Developer Portal offers buildable, executable source examples of how to accomplish a task using a particular technology in a wide variety of categories.   

Client libraries

Client libraries are chunks of code that developers can add to their own development projects. They are usually available in various programming languages, and cover basic functionality for an application to be able to interact with the API. Providing them is an extra feature that requires ongoing investment from the API provider, but doing so helps developers jump-start their use of the API. GitHub follows the practical approach of offering client libraries for the languages that are used the most with their API, while linking to unsupported, community-built libraries written in other, less popular languages.

Examples in multiple languages

APIs are platform- and language-independent by nature. Developers can use an API’s services with the language of their choice, but this means good documentation should cover at least the most popular languages used with that particular API (e.g., C#, Java, JavaScript, Go, Objective-C, PHP, Python, Ruby, and Swift). Not only should you provide sample code and sample applications in different languages, but also these samples should reflect the best-practice approach for each language.

Usability

API documentation is a tool that helps developers and other stakeholders do their job. You should adapt it to the way people use it, and make it as easy to use as possible. Consider the following factors:


  • Copy and paste: Developers copy and paste code examples to use them as a starting point for their own implementation. Make this process easier with either a copy button next to relevant sections or by making sections easy to highlight and copy.

  • Sticky navigation: When implemented well, fixing the table of contents and other navigation to the page view can prevent users from getting lost and having to scroll back up.

  • Clicking: Minimize clicking by keeping related topics close to each other.

  • Language selector: Developers should be able to see examples in the language of their choice. Put a language selector above the code examples section, and make sure the page remembers what language the user has selected.

  • URLs: Single page views can result in very long pages, so make sure people can link to certain sections of the page. If, however, a single page view doesn’t work for your docs, don’t sweat it: just break different sections into separate pages.
    Screenshot: A specific section of the Stripe API documents with the location bar showing that the URL has changed.
    Great usability: Stripe’s API documentation changes the URL dynamically as you scroll through the page.

    Another best practice from Stripe: the language selector also changes the URL, so URLs link to the right location in the right language.


  • Collaboration: Consider allowing users to contribute to your docs. If you see your users edit your documentation, it indicates there might be room for improvement—in those parts of your docs or even in your code. Additionally, your users will see that issues are addressed and the documentation is frequently updated. One way to facilitate collaboration is to host your documentation on GitHub, but be aware that this will limit your options of interactivity, as GitHub hosts static files.


Interactivity

Providing an option for users to interact with your API through the documentation will greatly improve the developer experience and speed up learning.

First, provide a working test API key or, even better, let your users log in to your documentation site and insert their own API key into sample commands and code. This way they can copy, paste, and run the code right away.

As a next step, allow your users to make API calls directly from the site itself. For example, let them query a sample database, modify their queries, and see the results of these changes.

A more sophisticated way to make your documentation more interactive is by providing a sandbox—a controlled environment where users can test calls and functions against known resources, manipulating data in real-time. Developers learn through the experience of interacting with your API in the sandbox, rather than by switching between reading your docs and trying out code examples themselves. Nordic APIs explains the advantages of sandboxing, discusses the role of documentation in a sandboxed environment, and shows a possible implementation. To see a sandbox in action, try out the one on Dwolla’s developer site.

Help

The study exploring how software developers interact with API documentation also explored how developers look for help. In a natural work environment, they usually turn to their colleagues first. Then, however, many of them tend to search the web for answers instead of consulting the official product documentation. This means you should ensure your API documentation is optimized for search engines and will turn up relevant results in search queries.

To make sure you have the necessary content available for self-support, include FAQs and a well-organized knowledge base. For quick help and human interaction, provide a contact form, and—if you have the capacity—a help-desk solution right from your docs, e.g., a live chat with support staff.

The study also pointed at the significant role Stack Overflow plays: most developers interviewed mentioned the site as a reliable source of self-help. You can also support your developers’ self-help efforts and sense of community by adding your own developer forum to your developer portal or by providing an IRC or Slack channel.

Changelog

As with all software, APIs change and are regularly updated with new features, bug fixes, and performance improvements.

When a new version of your API comes out, you have to inform the developers working with your API about the changes so they can react to them accordingly. A changelog, also called release notes, includes information about current and previous versions, usually ordered by date and version number, along with associated changes.

If there are changes in a new version that can break old use of an API, put warnings on top of relevant changelogs, even on top of your release notes page. You can also bring attention to these changes by highlighting or marking them permanently.

To keep developers in the loop, offer an RSS feed or newsletter subscription where they can be notified of updates to your API.

Besides the practical aspect, a changelog also serves as a trust signal that the API and its documentation are actively maintained, and that the information included is up-to-date.

Analytics and feedback

You can do some research by getting to know your current and potential clients, talking to people at conferences, exploring your competition, and even conducting surveys. Still, you will have to go with a lot of assumptions when you first build your API docs.

When your docs are up, however, you can start collecting usage data and feedback to learn how you can improve them.

Find out about the most popular use cases through analytics. See which endpoints are used the most and make sure to prioritize them when working on your documentation. Get ideas for tutorials, and see which use cases you haven’t covered yet with a step-by-step walkthrough from developer community sites like Stack Overflow or your own developer forums. If a question regarding your API pops up on these channels and you see people actively discussing the topic, you should check if it’s something that you need to explain in your documentation.


Collect information from your support team. Why do your users contact them? Are there recurring questions that they can’t find answers for in the docs? Improve your documentation based on feedback from your support team and see if you have been successful: have users stopped asking the questions you answered?