# Decisions - zugferd-service

This file accumulates architectural and design decisions during execution.

## [2026-02-04T18:12:44.864Z] Session Start
Planning decisions from Prometheus session.

## Tech Stack
- Python 3.11+
- FastAPI for REST API
- Pydantic for data validation
- pytest for testing
- factur-x library for ZUGFeRD extraction
- pypdf for PDF text extraction

## Scope Lock
- NO authentication (stateless service)
- NO database
- NO caching
- NO rate limiting
- 10MB file size limit
- 0.01 EUR tolerance for calculations

## Validation Rules
- pflichtfelder: Required fields check
- betraege: Amount calculations check
- ustid: VAT ID format check (no online validation)
- pdf_abgleich: XML vs PDF text comparison