Kontor

The Problem

German freelancers struggle with cluttered, bloated tools like Lexoffice or sevDesk. Most don't need full accounting – just quick invoices, expense tracking, and a year-end overview for their tax advisor. Existing tools cost 15-40€/month for features nobody uses.

The Solution

Kontor is the invoicing tool I've been using myself since 2020 – now available as SaaS for others. Focus on the essentials: create invoices in under a minute, categorize expenses, monthly reports. No accounting overhead, no hidden costs. 8€/month flat, unlimited team members.

Results

Architecture

Full-stack TypeScript with TanStack Router for client-side routing and TanStack Query for optimistic data fetching. Supabase (hosted in Frankfurt) as backend for GDPR compliance and low latency in the DACH region. Server-side PDF generation with print-optimized layout, email delivery via Resend.

Challenges

• • 5 years of tech stack evolution: From Firebase via Convex back to Supabase – each refactoring brought new insights
• • PDF layout: Pixel-perfect invoices that look the same on every printer, with automatic page break logic
• • German tax compliance: Reverse charge, small business regulation, correct VAT calculation based on customer country
• • Multi-tenant team system: Simple role system (Owner/Admin/Member) per organization

Learnings

• • Convex has fantastic DX, but for the German market GDPR compliance matters more – back to Supabase with EU hosting in Frankfurt
• • Building your own tools pays off: 5 years of use = deep understanding of real user problems
• • AI features are fun and add real value: auto-tagging, text generation, proofreading – even a wingman for finding fair hourly rates
• • DACH market has special requirements: QR codes for bank transfers, IBAN validation, German spelling in templates
• • Rebranding from 'Easy Invoice' to 'Kontor': No suitable domain available, and 'Kontor' sounds more trustworthy for a financial tool