A Practical Guide to Documenting Internal APIs

Keeping an internal API as readable, maintainable, and as valuable to third parties as possible is no small task. It requires extensive planning and documentation to ensure that new developers can easily understand how the code works and what it does.

A poorly documented API prevents external developers from using your code, which means they won’t be able to incorporate your functionality into their apps.

Unhelpful or incorrect documentation leaves little insight into whether a bug has been fixed or if a new feature is coming soon. Poorly organized API documentation leaves you searching through irrelevant files for the information you need. Thus, if your internal API isn’t well-documented, it will be significantly harder for other team members to understand its functionality.

Ineffective or unhelpful API documentation makes it difficult for developers who aren’t already familiar with the project to make changes or updates quickly and easily.

Misleading or unhelpful API documentation tricks new developers into thinking something is more straightforward, resulting in more time spent troubleshooting problems than necessary.

Internal API documentation is often overlooked and underappreciated, yet it’s one of the essential resources in your organization or project.

This post takes a practical approach to documenting internal APIs and why this is important to any company. Lastly, we’ll take a look at top API documentation tools. But before diving into how to document Internal APIs, let’s take a closer look at why API documentation is essential.

Why Is Internal API Documentation Important?

Internal API documentation is often overlooked and underappreciated, yet it’s one of the essential resources in your organization or project. Why is that? Below are some of the most important reasons why they’re crucial: 

1) It helps new developers save time to understand. When a new developer joins your team, it helps if they can quickly understand the system’s structure. You can do this by documenting your system’s internal API

2) It promotes asynchronous communications. When you have a team that’s working on different parts of the code, they’ll be working on various features of their own. And in order to keep everything in sync, it’s best to have a documented internal API.

3) It’s part of a design-first culture. Internal API documentation helps developers clearly see how the API will be used. This allows new developers to understand how to use the API and creates a development culture that promotes design first.

Now that you understand why documenting internal APIs is essential, let’s look at some standard best practices.

Also read Why You Need a Microservice Catalog

Making Time for Documentation

You’re not alone if you’re still not convinced that documenting your APIs is worth the time and effort. Although writing documentation isn’t something that developers like to do, making time is essential to keeping an API organized and helpful for new developers.

Keep an API documentation file open in a separate tab or window throughout the development process. Whenever you change the code, update the documentation file so you don’t forget to add it later. This will save you time down the road when you’re trying to remember what changed and why. Furthermore, it will help you track what has changed from one version to the next. It will also help you decide what features to add next and what needs to be fixed or removed from the current version. Therefore, with well-organized, helpful API documentation, you can easily track down any changes and additions that have been made. You can also spot and correct issues quickly and easily.

Reading Guide: Manage Engineering Initiatives with OpsLevel Campaigns

Best Practices to Adopt While Documenting Internal APIs

Documentation is a vital part of any API. It’s like the user manual for a software program. The documentation tells the user how to use the API and adequately integrate it into their application.

However, a lot of developers don’t pay much attention to it. They’re more interested in developing the API and making it work than ensuring that it’s easy for other developers to use and integrate.

Below are a few things that are extremely important for developers to take into account:

1) Keep it simple. If you’re documenting an API, it’s essential to keep your documentation straightforward. Otherwise, it might be more confusing than helpful.

2) Version the API. It’s crucial to version the API correctly when documenting it. Document each version and list what each version does and what it doesn’t do. State all requirements for each version as well.

3) Include code samples. Code samples are essential. They show users and developers how to use your API. You want to make sure that you design your code samples in a way that’s easy to understand.

4) State the prerequisites. State all API requirements, including specific software versions.

Whenever you change the code, update the documentation file so you don’t forget to add it later. This will save you time down the road when you’re trying to remember what changed and why.

Top Tools for Documenting Internal APIs

There are various tools for documenting APIs, but it can be challenging to find a perfect fit. Below are the best tools.

1. Swagger

Swagger is one of the most-used tools for documenting APIs. It offers paid (Swagger Hub) and free (Swagger UI) plans.

Swagger is an open-source framework for API specification. It provides a complete toolset to create, maintain, and document RESTful APIs. The framework offers SDKs in multiple languages and tools for building interactive documentation.

It uses JSON to model server APIs and employs YAML for the validation of the models. And it has become an industry standard for documenting REST APIs.

If you’re a NodeJS developer, you can generate API documentation automatically using the swagger-autogen npm module.

Check out sample Swagger Documentation.

2. Postman Collection

Postman has been a popular API client for a long time now and has improved with each update. The users were given the ability to generate documentation with the recent update. With Postman, you can create documentation with one click and even host it online. That way, you can keep your documentation up to date and share it with your team and clients to collaborate effectively.

To generate API documentation of your postman collection, click on the three dots near your collection and select “View Documentation.” Then, click on the “Publish” button in the top right corner to publish the documentation.

Note: You can easily connect a custom domain to your API documentation and make it available exclusively for internal use by only making it available over the VPN.

3. apidoc

apidoc is undoubtedly the simplest tool on this list. It’s also completely free to use, albeit without the same level of functionality as the paid tools. apidoc is a code-first documentation tool. This means that you don’t have to create any separate documentation files before running it. It pulls the relevant code and creates the documentation from there.

APIMatic offers support for a handful of different languages, including C#, Go, Dart, Java, JavaScript, PHP & Scala. apidoc is available for download using NPM with more than 80,000 downloads per week.

Note: You can easily set up a microservice to generate API documentation using CI/CD Pipelines and OpsLevel.


Internal APIs help bridge the gap between systems and make it easier to integrate disparate data. Documenting your internal APIs can be a critical part of your DevOps strategy, helping ensure a smooth integration, an easy way to troubleshoot errors, and much more.

OpsLevel is a modern service catalog for DevOps that enables organizations to rapidly deploy, operate, and manage their services and apps.

Easily track all your microservices and the team responsible for them. You can connect your Git provider as GitHub, BitBucket, or GitLab to look into your codebase. And that’s not all. Book a demo today to learn more.

We hope this blog post helps you understand why it’s essential to document your internal APIs and how you can do that. If you have any other questions or concerns regarding documenting your API, don’t hesitate to contact us any time.

This post was written by Keshav Malik. Keshav is a full-time developer who loves to build and break stuff. He is constantly on the lookout for new and interesting technologies and enjoys working with a diverse set of technologies in his spare time. He loves music and plays badminton whenever the opportunity presents itself.

Learn how to grow your microservice architecture without the chaos.

Not ready for a demo? Stay in the loop with our newsletter.