AI Coding · 2026-05-15

How to Use AI for API Documentation

Generate clear API documentation from your code using AI without writing a single doc block manually.

Introduction

Writing API documentation is every developer's least favorite task. You know how your code works, but writing clear explanations for other developers takes time. AI can generate accurate documentation directly from your code or route definitions.

Here is how to document your API endpoints fast using AI.

Step 1: Generate Docs From Code Comments

The quickest method is to paste your route handler code and let AI generate the documentation.

Try this Prompt:

Generate OpenAPI-style documentation for the following Express route handler. Include:
- A short description of what this endpoint does.
- Request parameters (path, query, body).
- Example request and response.
- Possible error responses.

[paste your route handler code here]

Step 2: Generate Examples for Each Endpoint

Good documentation includes realistic examples. AI can generate them from your data models.

Try this Prompt:

Given this data model for a [User] object:

interface User {
  id: number;
  name: string;
  email: string;
  role: "admin" | "user";
  created_at: string;
}

Generate example JSON responses for:
1. GET /users (list of users).
2. GET /users/:id (single user).
3. POST /users (create user with request body).
4. PUT /users/:id (update user).
5. DELETE /users/:id (delete user).

Step 3: Update Existing Documentation

If you already have documentation but it is outdated, AI can help you update it.

Try this Prompt:

Here is my existing documentation for a /users endpoint, and here is the updated code. Identify what has changed and rewrite the documentation to match the new code.

Existing docs:
[paste old docs]

Updated code:
[paste new code]

FAQ

Can AI generate documentation for private/internal APIs?

Yes. AI works best with clear input, so private APIs with well-named functions get good results. Just avoid pasting sensitive authentication tokens or secrets.

Should I use AI-generated documentation directly?

Review it first. AI sometimes invents parameters or response fields that do not exist in your actual code. Always test the documented endpoints to make sure the examples match reality.

Related Tutorials

• /tutorial/how-to-explain-complex-code-with-ai
• /tutorial/how-to-use-ai-to-write-unit-tests