Engineering Notes
Tech Blog
Notes on conversational AI, e-invoicing infrastructure, and the engineering decisions behind Kaepsi and invoice24.
Building a Conversational Invoice Engine on WhatsApp
How we designed a three-layer architecture to transform unstructured WhatsApp messages into structured, legally compliant invoices, with no app to install and no form to fill in.
From Voice Message to Signed PDF in Thirty Seconds
A detailed look at the AI extraction pipeline inside Kaepsi: from Whisper transcription through Claude-powered structured extraction to geocoded address validation and signed PDF delivery.
Typed State Machines for Conversation Context
How we eliminated runtime type errors in session context handling by introducing typed accessor interfaces, and why untyped JSON in a conversational system is a maintenance liability.
Belgium's E-Invoice Mandate and How We Built invoice24.be in Eight Weeks
Since January 2026, Belgian B2B invoices must be exchanged in a structured electronic format. We built invoice24.be, a batch PDF-to-Peppol converter, in eight weeks. Here is what we learned.
Address Validation as a Conversation Design Problem
When a tradesperson types 'Musterstr. 3 Frankfurt', should the system accept it, correct it, or reject it? We treat address validation not as a technical detail but as a user experience problem, and the difference matters.