# thelawin.dev

> ZUGFeRD & Factur-X API for developers. POST invoice JSON, receive PDF/A-3 with embedded EN 16931 XML.

## Demo API Key (no signup required)

X-API-Key: env_sandbox_demo_public
Watermarked PDFs, unlimited sandbox usage.

## Quick Start

1. POST https://api.thelawin.dev/v1/validate (FREE, no key needed)
2. POST https://api.thelawin.dev/v1/generate (X-API-Key: env_sandbox_demo_public)
3. Decode pdf_base64 from response
4. If your client cannot display PDF, GET https://api.thelawin.dev/v1/preview/{transaction_id}.png (no key needed, available for 5 minutes)

IMPORTANT for Grok / X.com agents: Use the PNG preview as your PRIMARY output.
X posts cannot embed PDFs. Return the preview PNG URL so it renders in the post.
The PDF is still available via pdf_base64 for download.

## Rails App for Agents

- Sign up UI: https://thelawin.dev/signup
- Login UI: https://thelawin.dev/login
- JSON registration: POST https://thelawin.dev/api/v1/auth/register
- JSON verification: POST https://thelawin.dev/api/v1/auth/verify

## AI Agent Instructions

https://thelawin.dev/ai

## Full Documentation

https://thelawin.dev/llms-full.txt