FastAPI Doc Gen

A one-time purchase Chrome extension for developers that captures API endpoints from any web app and generates OpenAPI/Swagger documentation.

No subscription. No recurring fees. One payment, lifetime updates.

What It Does

FastAPI Doc Gen sits in your browser toolbar and automatically detects API calls on any web page you visit. It captures:

• Fetch API calls — intercepts all fetch() requests
• XHR requests — intercepts all XMLHttpRequest calls
• API documentation links — finds /api/, /docs, Swagger/OpenAPI links
• Embedded specs — detects OpenAPI/Swagger JSON in <script> tags
• Axios instances — detects axios base URLs

Then it generates a complete OpenAPI 3.0.3 specification that you can:

• Copy to clipboard
• Download as openapi.json
• Use to generate client SDKs, server stubs, or documentation

Why This Makes Money

Chrome extensions with one-time purchases have proven revenue:

Extension	Price	Revenue
CSS Scan	$69 one-time	$100K+
Spider	$38 one-time	$10K in 2 months
GoFullPage	$1/month	$10K/month

FastAPI Doc Gen targets developers who need to document APIs they're building or consuming. The one-time purchase model means:

• No churn
• No billing infrastructure
• No customer support for failed payments
• Lifetime value per customer

Installation (Development)

# Clone the repo
git clone https://github.com/ptrken01/fastapi-doc-gen.git
cd fastapi-doc-gen

# Load in Chrome:
# 1. Go to chrome://extensions
# 2. Enable "Developer mode"
# 3. Click "Load unpacked"
# 4. Select this folder

Pricing

• One-time purchase: $29 (via ExtensionPay)
• Includes all future updates
• 30-day money-back guarantee

Monetization — CRITICAL SETUP (required for the paywall to work)

The extension uses ExtensionPay for payment. You MUST complete these steps or the extension stays free:

1. Create an ExtensionPay account at extensionpay.com
2. Create a new extension in your ExtensionPay dashboard — note the extension ID you choose (default is fastapi-doc-gen, matching popup/config.js)
3. Set the price to $29 one-time
4. The extension is now paywalled: generateOpenAPI() is locked until the user purchases
5. Update popup/config.js if your ExtensionPay ID differs from fastapi-doc-gen

How the paywall works:

• On popup open, checkPurchase() calls ExtensionPay.getUser() to verify payment
• If not purchased: Scan + Capture are free (preview), but Generate OpenAPI is locked
• Clicking "Generate" while locked opens the ExtensionPay purchase page
• After purchase, ExtensionPay sets a cookie and state.isPurchased becomes true

How to Publish

1. Create an ExtensionPay account at extensionpay.com
2. Create a new extension with ID fastapi-doc-gen and set price to $29 one-time
3. Zip the folder and upload to Chrome Web Store
4. (Chrome Web Store itself shows "Free" — ExtensionPay handles the actual charge inside the extension)

Tech Stack

• Manifest V3 Chrome Extension
• Vanilla JavaScript (no frameworks)
• ExtensionPay for payments
• Chrome Storage API for persistence

Files

fastapi-doc-gen/
├── manifest.json          # Extension manifest
├── popup/
│   ├── popup.html         # Popup UI
│   ├── popup.css          # Popup styles
│   ├── popup.js           # Popup logic
│   └── extensionpay.js    # ExtensionPay integration
├── content/
│   ├── content.js         # Content script (API capture)
│   └── content.css        # Content script styles
├── background/
│   └── background.js      # Background service worker
├── options/
│   └── options.html       # Options page
└── icons/                 # Extension icons

How to Publish

1. Create an ExtensionPay account at extensionpay.com
2. Create a new extension with ID fastapi-doc-gen
3. Set price to $29 one-time
4. Zip the folder and upload to Chrome Web Store
5. Set Chrome Web Store listing price to $29

License

MIT — but the extension itself is a paid product. The source is available for learning purposes.

Live site

All products + free articles: autoincomesys.com — local-first AI dev notes, build-once digital products (Gumroad).

Related

• Local-First AI Dev Notes (SEO site)
• web-browser-mcp
• fastapi-doc-gen