How to Write API Documentation?

Are you interested in knowing how to write API documentation?

The landscape for APIs is growing immensely. The global API market size is projected to reach a value of $8.41 billion by 2027. The reason for this growing market is the easy accessibility APIs offer to various software services without any need to develop them from scratch.

An API connects different software applications running on different devices with external software resources. However, to achieve this successfully, software developers need complete and well-written API documentation. 

Great API documentation is a complete guide stating the functions of APIs, how to use and integrate them into your software application, some use cases, and examples for better understanding.

Let’s see in detail how you can write API documentation effectively for software developers.

Steps to Writing API Documentation

You will go through the following steps to produce engaging and interactive API documentation.

Get yourself acquainted with the API 

You must know the ins and outs of the API you are writing about. Your writing will help developers use API services efficiently. Insufficient knowledge on your part will result in poor documentation that will leave users confused. 

So, as a first step, gather all the information related to the API. What are its functions, how to use it, its request and response formats and parameters, how to use it with other product features, etc.?

You can also take the help of subject matter experts and software developers developing APIs to give you correct information.

Decide the type of API documentation

There are three types of API documents. These are reference, tutorial, and conceptual. 

Reference API document explains all the functions of an API, including parameters, output values, etc.

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Tutorials are detailed instructions on how to use APIs for different use cases. They explain using different parameters, endpoints, etc., in quite a detailed manner so that software developers get an idea of how they can apply it to their business problems.

Conceptual documentation explains how a complete application can be built using certain APIs. It not just focuses on one API and its functions but explains the integration of multiple APIs in a single application.

Deciding on the type of API docs will help you plan the end goal of the API document. You will also easily create an outline for the documentation, keeping in mind what the target audience expects from it, including scenarios on how to use an API, detailed explanations of a specific API and its methods, etc.

Start by presenting an interesting abstract

Now, you can start with the first section of API documentation and which is an overview. An overview introduces your API to the expected users, just like an abstract of a document. Therefore, it should be interesting and immediately mention the role of your readers in using the API. 

Clearly state what users will get by integrating your API into their software product.

Take an example of Canva API for app development. The overview starts by stating that API is intended for users interested in building apps that add features to the Canva platform.

Provide a starting point for developers

Now, that new users are interested in using your API, provide them with a starting point. Technical documentation such as an API document contains technical jargon and can get complex. There is also a lot of information related to different aspects of API architecture. 

One thing you can do to make document navigation easier is to provide a clean structure in your API documentation. Clearly mention where and how software developers can start using your APIs in their software.

Continuing with Canva app development API documentation, it strategically lists downs the first steps that new users are expected to take right after the overview, which includes a Quick Start Guide.

List all the common use cases of your API

In the next step of how to write API documentation, mention all the common use cases of your API. This will help software developers looking to use your API services find the use case relevant to them. 

You should spend some time researching the types of solutions your expected users would be trying to build. Display the relevant APIs and their functions upfront but in a logical sense or some form of categories.

Take a look at Twitter documentation and see how they display the possible use cases of their APIs under the What to Build section. Each use case contains relevant endpoints, sample apps, and success stories. 

In this way, a new user instantly gets an idea of various possibilities of using a specific API and also gets an insight into a real-world case study. 

Include other important sections

Other than an overview and major use cases, add an authentication section. The authentication and authorization part helps developers get API keys to make authentic calls to your API services. 

This will include getting API tokens, their expiration times, and general instructions on how to keep API keys secure.

Another important section is status codes. It is important to show the error codes with API endpoints where they are most likely to occur. This will help users understand API response behavior quickly.

You can also provide a section on how to make HTTP requests. Although web developers are expected to know how to write HTTP request code and decipher response format, still most of the API documentation shows how to get started with HTTP request calls in different languages.

As a technical writer, you can do that automatically with either an API specification tool or An API management tool.

Standardize your API documentation

At this point, make sure your whole API document is in a standard format. Following a document standard format will make your writing consistent. Your document users will also find it easier to navigate your API documentation and find the required information placed logically.

In the software industry, OpenAPI specification has become a standard now for documenting REST APIs. OpenAPI specification was previously known as Swagger Specification, and according to the State of API survey, 70% of survey participants reported to be using OpenAPI/Swagger standard for their API documentation. 

The API specification is like a template for all your API documents. It uses a unified language that explains the design of your API, its various functions, endpoints, etc. Some other API specifications apart from Open API are RAML (RESTful API modeling language), GraphQL, Amazon API gateway, etc.

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The API document standard makes it understandable for both machines and humans. This helps you use API documentation tools that can automatically update your API definition into interactive documents. 

Swagger UI is one such documentation tool to visualize and use API information generated automatically from your OpenAPI specification.

Present tutorials and FAQs

Tutorials on how to incorporate your APIs in different projects will help users visualize the usability of your API service. 

Twilio API documentation is a good example of how to present API tutorials to help users understand how to use your APIs easily. 

Moreover, Twilio presents a code editor to display coding examples of using different APIs in multiple programming languages like Python, C#, Node.js, Java, etc. This lets developers tweak the existing coding examples and start with their own API integrations. 

An FAQ section helps users to look for answers to common questions. API documentation is not just a technical explanation but also a way to present your business. If users get what they are looking for instantly, they are more likely to come back again.

An FAQ section will help intended users save time while planning how to integrate your APIs into their products, as their queries will be immediately answered, without making any customer support calls.

Ask for feedback

Customer feedback is always important for every kind of business as it helps to improve product/service quality. Improved product quality means increased customer satisfaction and ultimately increased business growth.

An effective way is to make use of both qualitative and quantitative techniques to gauge users’ responses. 

For example, you can conduct surveys and ask users how useful they find your API documentation while performing integrations into their software applications. Moreover, what kind of improvements would they like to see? Such surveys may get difficult to conduct, especially with a large user base.

In addition to quantitative surveys, you can measure metrics like page visits, number of API calls, etc. 

Another thing to consider is to get documentation feedback within the document. You can insert a poll at the end of the documentation page asking if the documentation was useful or not. Most likely, most of the users will leave their feedback while skimming through API documentation.

Microsoft has a similar feedback option at the bottom of its documentation page. 

Keep up with document maintenance

Keeping up with timely updates of API documentation is extremely important. Nothing turns off software developers more than outdated technical documentation. There is a common practice of updating docs after updates have been rolled out. 

According to the State of API report, three reasons for outdated API documentation were:

• Huge workload resulting in insufficient resources and time for reviewing docs and making updates.
• Requirement of fast delivery.
• Insufficient supporting tools and technologies.

A few things you can do to perform better maintenance of your API documentation are:

• Make documentation updates a part of your API updates release plan. Try not to leave it as a post-deployment task.
• Start preparing docs beforehand so that you can publish your updates on time.
• Perform periodic reviews of your API documents. Remove any deprecated data still there. 
• Make use of API analytics. Focus more on API endpoints that are more frequently in use. Similarly, keep on improving use cases popular among the API users. You can provide more examples, tutorials, etc., to add more value there and present users with more possibilities via your API services. 
• To make time for updates and maintenance, make use of documentation tools. API documentation software tools like Postman and SwaggerUI help automate a number of repetitive tasks like converting API definitions to documents, etc.

Some Tips to Write Good API Documentation

Consider the following points to produce compelling API documentation.

Keep it conversational

API documents are technical explanations of APs. They are meant to be complex. However, do not complicate by using a high-flown language style. The best way is to explain technical details conversationally. 

You can also use a readability tool to analyze parts of your writing that can be made more simple and easy to read.

Write comprehensively

Do not assume anything ‘self-explanatory’. Your new users can vary depending on their skills and experience level. Explain each point with enough context that helps readers grasp the concept. 

However, you do not want to flood users with all the information. This is where a document structure like a hierarchy helps them navigate to the desired documentation sections quickly.

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Make it interactive

An interactive API document with visuals, a code editor, or a web-based IDE helps developers get familiar with your API more effectively. 

They can intuitively explore by making sample API calls via sample keys and getting responses instantly. 

This also gives a better understanding of parameters and methods specific to your API service like authorization, insertion of API key values, error messages, etc.

Follow an API documentation template

It is better to use an industry-standard functional layout for your API documentation. This will help to display a high volume of complex information efficiently. 

A common structure practice is to use a three-column layout. It lets you have another column on the right side to add code editor or code examples. 

Moreover, the layout should be dynamic. Static API documentation gives an outdated feel. A dynamic document can be easily navigated and bookmarked. 

Similarly, a sticky content bar always keeps the important sections in sight and helps in quick navigation.

Planning to Write the Best API Documentation?

API document is important technical documentation that is read by a range of users, including software developers, CTOs, testers, etc. These professionals will initially visit it as reference documentation to see if they can integrate your API services into their software applications. 

A captivating introduction will help them understand the goals they can achieve using your APIs. 

Similarly, once they start consulting your documentation for API reference and integration process, a clear and concise text with a logical flow and supporting examples and tutorials will offer them a fulfilling experience, increasing their chances of coming back again.

All this can be achieved if you have a competent technical documentation team. API developers build APIs, but they can not be given the responsibility of writing, editing, and maintaining the API’s documentation process. Also, writing documentation does not come naturally to everyone. 

Moreover, technical documents are complex, and the key is to convey complex details understandably. 

Read our guide here on how to write technical documentation.

If you do not find the required skills for writing API docs in your product team, take assistance from a credible software development agency with experienced knowledge experts and technical writers.

DevTeam.Space can also help you with its field-expert software developer community with your next software development or API documentation process.

Write to us your initial requirements via this form, and one of our account managers will get back to you for further assistance.

FAQs on How to Write Good API Documentation