More organizations are leveraging the power of APIs to optimize their business. APIs have become a way to unlock value and provide an extra service.

Despite their general popularity, not every API is a success. The adoption and use of an API largely determine its success. To increase adoption, your API needs to be easy to find and use.

The best way to do this is by documenting your API in detail. This includes detailing critical components to make them easier to understand. Find out some of the components that you should include in your API documentation.

What Is API Documentation?

API documentation is technical content that describes an API in detail. It's a manual containing all the information required to work with the API. The document covers the API lifecycle and instructions on integrating and using its components.

API documentation covers resource descriptions, endpoints, methods, requests, and response examples. It can also include practical guides and tutorials showing users how to integrate it. Exploring each section gives users a solid understanding of integrating and using the API.

Editors like Google Docs were once widely used for professional API documentation. Nowadays, there are more advanced tools like Document 360, Confluence, and GitHub Pages. These tools help to integrate text and code for easier workflows.

1. Overview and Purpose of the API

The first step in documenting an API is letting users know what it's about. Include information about the type of resources it provides. APIs usually have various resources they return, so the user can request what they need.

The description is brief, usually one to three sentences that describe the resource. Describe the available resource, the endpoints, and the methods attached to each endpoint. As the API developer, you best describe its components, functionality, and use case.

Here's an example of a description of the Airbnb API:

2. Authentication and Authorization Methods

APIs handle thousands of requests and enormous amounts of data. Authentication is one of the ways to ensure the data of your API and users is secure from hackers. API Authentication verifies a user's identity and gives them access to resources.

There are several ways to ensure endpoint security. Most APIs use an API key. This is a string of characters that a user can generate from the website and use for authentication.

The API documentation should guide users on how to authenticate and authorize their identities. The following diagram shows Twitter API authentication information.

3. Endpoints, URI Patterns, and HTTP Methods

In this section, demonstrate how to access the resource. The endpoints only show the end of the path, hence their name. They show access to the resource and HTTP methods the endpoint interacts with, namely GET, POST, or DELETE.

One resource likely has a variety of endpoints. Each with a different path and method. Endpoints usually have brief descriptions of their purpose and a URL pattern.

The following code sample shows a GET user endpoint on Instagram.

        GET /me?fields={fields}&access_token={access-token}
    

4. Request and Response Formats

You must document the request and response formats so the user knows what to expect. The request is a URL from a client asking for a resource, while the response is feedback from the server.

The following is a sample request that you can send to the LinkedIn API.

        GET https://api.linkedin.com/v2/{service}/1234
    

And here’s a sample response that it can return:

        {
    "id": 1234,
    "relatedEntity": "urn:li:relatedEntity:6789"
}
    

5. Parameters and Headers

You should also document your endpoints’ parameters, which are options that you can pass to them. Parameters can be an ID or number that specifies the amount or type of data returned in response.

There are different types of parameters, including header, path, and query string parameters. The endpoints can contain different types of parameters.

You can include some parameters as HTTP request headers. Usually, these are for authentication purposes like an API key. Here's an example of a header with API keys:

        headers: {
    'X-RapidAPI-Key': 'fd40ada866msh4d8b69e4aa2dd19p12e47fjsn7efdcbc75635',
    'X-RapidAPI-Host': 'wft-geo-db.p.rapidapi.com'
}

    

You include path parameters in the body of the endpoint right on the URL. They show a user how and where to place the parameters and how the response will appear. The words in curly braces are parameters.

You can also use colons or other syntax to represent path parameters.

        /service/myresource/user/{user}/bicycles/{bicycleId}
    

With query parameters, you must place a question mark (?) before the query on an endpoint. Separate each parameter after that with an ampersand (&). Microsoft has good documentation on the Graph API.

6. Error Codes and Error Handling

Sometimes HTTP requests fail, which can leave a user confused. Include expected error codes in documentation to help users understand the errors.

LinkedIn provides standard HTTP error codes for error handling:

7. Sample Code Snippets

Code snippets are essential parts of your documentation. They show users how to integrate the API in various languages and formats. Include how to install and integrate SDKs (software development kits) in various languages in the documentation.

RapidAPI has good examples of code snippets for developers:

9. API Versioning and Change Logs

API versioning is an essential part of the API design. It ensures the delivery of uninterrupted services to your users. Versioning can enhance the API with new versions without affecting client applications.

Users can continue using older versions or migrate to advanced ones in time. If there are new changes to the logs, Include them in the documentation so that users are aware.

Microsoft Graph API has well-documented change logs:

10. Contact Information for Support and Feedback

Finally, include important contacts in the documentation for support and feedback. These ensure that users can reach you with error reports and information on how to improve the API.

The Value of API Documentation

If you build an API for commercial value, consumption determines its success. And for users to consume your API, they must understand it.

Documentation brings an API to life. It explains the components in detail in simple language that sells its value and usage to users. Users will happily consume your API if they have a great developer experience.

Good documentation also helps to simplify the maintenance and scaling of the API. Teams working with the API can use documentation to manage it.