I made an invoice PDF API that doesn't need a headless browser

#api #webdev #showdev #python

Generating a PDF shouldn't require a headless browser

Every time I needed to generate an invoice or receipt PDF, the options were:
wrestle a low-level PDF library, fight a templating engine, or spin up headless
Chromium (slow, heavy, breaks on fonts, painful to host). For a document, that
felt absurd.

So I built InvoicePDF: POST JSON, get a clean invoice PDF back.
That's the whole thing.

curl -X POST https://invoicepdf-app.azurewebsites.net/invoice \
  -H "Content-Type: application/json" \
  -d '{
    "number": "INV-2026-001",
    "currency": "USD",
    "seller_name": "Your Company LLC",
    "buyer_name": "Acme Corp",
    "items": [
      { "description": "Consulting (hours)", "quantity": 8, "unit_price": 120 },
      { "description": "Software license", "quantity": 1, "unit_price": 299 }
    ],
    "tax_rate_percent": 10,
    "notes": "Thank you!"
  }' --output invoice.pdf

Why pure Python (no chromium)

It's built on fpdf2 — a pure-Python PDF library — so there's no headless
browser and no system dependencies. That means it starts instantly, uses
almost no memory, and deploys on a free tier like a static app. For structured
documents (invoices, receipts, statements), you don't need a browser; you need
correct layout and correct math.

The money math is exact

Financial documents can't have floating-point drift. InvoicePDF does all money
as integer minor units (cents/paise) internally, so $27.00 subtotal + 10% tax is exactly $29.70 — never $29.700000001. It handles multiple currencies
(including zero-decimal ones like JPY), fractional quantities (e.g. hours), tax,
notes, and due dates.