decaf: Italian Modello Redditi PF on foreign investments (without a commercialista)

Sat, 18 Apr 2026 00:00:00 +0000

If you hold foreign investments as an Italian tax resident, you know the drill. Every spring you bundle a stack of PDFs and broker exports, send them to your commercialista, and a few weeks later you get back a PDF that costs between three hundred and eight hundred euros and which you have no way of verifying because you don’t speak TUIR fluently.

A project like decaf, until recently, wouldn’t have been an evenings-and-weekends project: reading the TUIR, Agenzia delle Entrate circolari, and interpello responses isn’t my job, and doing it with enough precision to bet a tax filing on it takes months. With an Artificial Intelligence that chews through the legislation alongside me and keeps me honest, it became feasible. The result is decaf-tax on PyPI and github.com/vjt/decaf on GitHub, MIT-licensed. With a test suite built specifically to keep me from fudging numbers: synthetic cases with their expected outputs stored next to them, plus three years of my own real filing — the one validated by the commercialista — used as an ongoing reference. I’ll unroll the technical details below.

Foreign-Investments on Marcello Barnaba

decaf: Italian Modello Redditi PF on foreign investments (without a commercialista)