# Build a Sleeping Income Machine: Auto-Generate and Sell Niche API Documentation with AI

> Source: <https://dev.to/sinan_koak_4a6dea677278a/build-a-sleeping-income-machine-auto-generate-and-sell-niche-api-documentation-with-ai-3ce5>
> Published: 2026-08-09 15:00:33+00:00

Most developers chase passive income by building SaaS tools or selling courses. But there's a quieter opportunity hiding in plain sight: **automated API documentation generation for niche industries**.

Here's the exact system I built that now earns consistently without daily intervention.

Thousands of small API providers — payment processors for specific regions, logistics APIs for emerging markets, healthcare data aggregators — have terrible documentation. Their developer adoption suffers. They'll happily pay $200-500/month for clean, maintained docs.

``` python
import requests
from bs4 import BeautifulSoup

def fetch_openapi_spec(url):
    response = requests.get(url)
    return response.json()  # Most APIs expose /openapi.json
```

Target APIs that have specs but poor human-readable guides. Search GitHub for `openapi.json`

files from companies with under 500 stars.

For each endpoint, send a structured prompt:

``` python
def generate_endpoint_doc(endpoint_data):
    prompt = f"""
    Write developer documentation for this API endpoint.
    Include: description, use cases, code examples in Python and JavaScript,
    common errors, and pro tips.

    Endpoint data: {endpoint_data}
    """
    # Call OpenAI API here
    return gpt4_response
```

Cost per full API documentation set: roughly **$0.40-$1.20** using GPT-4o.

Schedule weekly regeneration to keep docs current:

```
name: Regenerate Docs
on:
  schedule:
    - cron: '0 2 * * 1'  # Every Monday at 2am
jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - name: Generate and deploy
        run: python generate_docs.py && npm run deploy
```

Offer three tiers on a simple landing page:

| Tier | Price | Includes |
|---|---|---|
| Starter | $197/mo | 1 API, monthly updates |
| Growth | $397/mo | 3 APIs, weekly updates + changelog |
| Agency | $797/mo | Unlimited APIs, white-label |

Conversion rate from free sample: roughly **22%** in my experience.

API providers rarely churn because switching means rebuilding developer trust. Once your docs become part of their onboarding flow, you're embedded in their business. Every new endpoint they ship becomes a natural upsell conversation.

The AI handles the heavy lifting. You handle the relationships.

**Start with one free sample doc this weekend.** The entire build takes about 6 hours, and your first paying client could follow within two weeks.

What niche APIs are you thinking about targeting? Drop a comment below — happy to help brainstorm your angle.