How to Write API Documentation with AI Agents

Writing API documentation is slow and easy to skip. Here's how to use AI agents to produce clear, complete reference docs in a fraction of the time.

API documentation is the last thing solo founders write and the first thing their users complain about.

If you've shipped an API, you know the pattern. You spend weeks building it, then documentation gets pushed to "later." Later arrives when a developer emails asking what parameters your endpoint accepts or why they're getting a 422. You spend an hour explaining something that should have taken them 30 seconds to find in the docs.

AI agents can handle most of the documentation work. Here's how to do it without starting from scratch every time.

What API Documentation Actually Needs

Before you put an agent to work, know what you're building. A complete API doc set has five parts:

Endpoint reference: Every route, method, parameter, and response schema
Authentication guide: How to get credentials and authenticate requests
Getting started guide: A working example from zero to a successful first call
Code examples: At least curl plus one SDK language
Error reference: Every error code with its cause and resolution

Skip any of these and developers fill in the gaps with support tickets.

How to Write API Docs with AI Agents

The Specialized department includes an API Documentation Writer agent built for exactly this. Pair it with the Technical Writer from Engineering and you cover the full scope. Here's the process:

Export your API spec: Pull your OpenAPI/Swagger JSON, or write out each endpoint with its method, path, parameters, and expected response. This becomes the agent's source of truth. Do not hand it your application code — implementation details don't belong in docs and produce noisy output.
Generate the endpoint reference: Feed the spec to the API Documentation Writer. Ask it to group endpoints logically (authentication, orders, webhooks, etc.) and produce a reference page per group. It will generate parameter tables, required vs. optional flags, example request bodies, and response schemas.
Write the getting started guide: This is the page developers read first. Give the Technical Writer three inputs: your auth method (Bearer token, API key, OAuth), your base URL, and one sentence describing who your typical developer is. Ask it to produce a quickstart: get credentials, authenticate, make the first call, verify the response. This page determines whether a developer integrates or gives up.
Generate code examples: Ask the API Documentation Writer to write curl examples for every endpoint, then SDK examples in the languages your users are most likely to use. For most products, Python and JavaScript cover the majority. Developers copy-paste code examples more than they read prose.
Document error codes: Give the agent your full list of error codes and ask it to write one clear paragraph per code: what triggered it, and what the developer should do to fix it. This is the section that gets searched at 11 pm when something breaks in production.
Review the output: Read every page as if you've never seen your API. Remove anything that assumes prior context. Add cross-links between related sections. Fix anything the agent got wrong about your specific business logic.

A Real Example

Say you've built a subscription billing API with 14 endpoints. You have a Swagger file but no documentation.

Start with the API Documentation Writer. Feed it the Swagger JSON and ask it to group the endpoints: plans, subscriptions, invoices, webhooks. For each group, ask for a full reference page with parameter tables and example responses. What normally takes a full day comes back in under an hour.

Next, give the Technical Writer your authentication method (Bearer token from the dashboard) and a one-line description of your typical user (a developer adding subscriptions to a SaaS product). Ask for a getting started guide. It produces: create an account, copy your API key, make a test call to create a plan, verify the response. Clear enough that a developer can follow it cold.

Then ask the API Documentation Writer to generate curl and Python examples for every endpoint. Copy them into your reference pages.

You now have documentation that covers all five parts. The review and editing pass takes about an hour.

Common Mistakes

Skipping the getting started guide. Developers don't read reference docs until they've made a successful first call. Without a quickstart, many give up before reaching the reference section.

Giving the agent your code instead of your spec. Code has private implementation details, internal variable names, and comments that don't belong in external docs. A clean spec produces cleaner output.

Only generating curl examples. If your user is building in Python and you only have curl, they'll spend time translating before they can test anything. That friction is avoidable.

Treating docs as a one-time task. Every time you add an endpoint or change a response schema, run the agent again on that section. Outdated documentation is worse than no documentation because developers debug based on what the docs say, not what the API does.

Bottom Line

API documentation looks like writing but is mostly structure. Structure is what AI agents do well. The API Documentation Writer can produce a complete reference set from a spec in under an hour. The Technical Writer turns it into a getting started guide that actually works.

You still need to review the output and fix what the agent got wrong about your specific logic. But reviewing is faster than writing from scratch, and that's where the time is.

Ready to put this into practice? Browse the departments and start with whichever handles your biggest current bottleneck.