API Documentation with Swagger – A Complete Beginner’s Guide

An API (Application Programming Interface) allows one application to interact with another. It helps programs connect with libraries and system applications. APIs are especially useful when building graphical user interfaces. A well-designed API is created in small, modular parts and then combined for full functionality.

Why API Documentation is Important

Almost every modern application depends on APIs. To help developers use your API, it must be clearly documented and easy to follow. Good documentation determines how successful your API becomes.

When external APIs are not well documented, developers often avoid using them to prevent future complications. In contrast, API documentation with Swagger makes it simple to maintain and update APIs whenever needed.

Strong documentation also improves teamwork. Developers can easily understand how each endpoint works and what responses to expect.

Guidelines for Good API Documentation

1. Authentication – Define who can access and use the API.
2. Change Log – Add updates gradually to keep track of changes.
3. Terms of Use – Clearly state how users can use the API.
4. Error Messages – Provide clear and correct error messages. Whenever possible, add simple steps to fix common issues.
   

Automated API Documentation

Today, many frameworks support automated API documentation. Swagger is a leading open-source tool that helps developers build and document RESTful APIs quickly and accurately.

Swagger UI

Swagger UI is easy to use and very developer-friendly. You only need to include Swagger in your application and create your API endpoints. It automatically generates the documentation for you.

As shown in Figure 1.1, the endpoint (https://testdomain.com/contact-us) offers request methods like POST, GET, and PUT.

Manually writing documentation often leads to errors and takes a lot of time. Instead, Swagger Editor allows you to design APIs using OpenAPI Specifications (OAS). It checks the data before the API call and gives real-time feedback, helping you fix problems early.

The editor also validates your design, ensures OAS compliance, and provides visual feedback instantly. Because of this, API documentation with Swagger saves both time and effort.

Visualize and Create APIs

When developing APIs, visualization helps you make them clear and user-friendly.

In Figure 1.2, the GET API for “university” expects different parameters. Swagger UI simplifies this by displaying input boxes where you can enter parameters directly. It also allows you to define which parameters are valid.

Developers can combine Data Transfer Objects (DTOs) with APIs to ensure only the required data is included. Any extra fields are automatically ignored. Swagger also documents responses and status codes, showing developers what to expect from each call.

Usage

Using Swagger is simple and straightforward. Visit its official website at https://swagger.io/ to get started. Then, create endpoints, choose request methods, and marshal the data returned from each API call.

As shown in Figure 1.3, even if your API retrieves all records from a database, only the fields defined in the marshal are included in the response. This keeps your API documentation with Swagger clean and consistent.

Conclusion

If you have never documented your APIs before, Swagger is the best tool to start with. It’s simple, well-documented, and easy to use. I have personally used it, and the process was quick and smooth.

Ricky Noronha