AI, taken apart.

I'm Xabier, a third-year AI engineering student in Madrid. I take AI systems apart to see how they work and where they break: agent harnesses, evals, and the insides of models.

// It started with Minecraft mods. Now it's language models.

See the teardowns ↓ Read the blog →

Profile

NameValue
Drawn by Xabier Ariznabarreta
School AI Engineering, year 3, Universidad Francisco de Vitoria
Email xabier.ariznabarreta [at] gmail (dot) com
GitHub @Xabilimon1

Latest note

2026-08-03 6 min read

LinceReservations: the constraints you don't get to choose

I built a room-booking platform for my university's study spaces, designed around the institution's own rules. It isn't deployed yet. The hard part was never React. It was everything the institution had already decided for me.

Teardowns

SAM

closed source sam.mp4

Read the writeup →

about: LLM agent over the CRM of a firm that maintains 2,500+ building exteriors, serving Salesforce and an Android app from one engine.
parts: fastapi, vertex ai, salesforce, cloud run
broke at: Instructions were dropped silently on the way to the model; everything still looked fine.

LinceReservations

closed source lince.mp4

Read the writeup →

about: Study-room booking for a Madrid university, built to its rules: OTP and Microsoft SSO, row-level security, five languages. Pending adoption.
parts: react, typescript, supabase, msal
broke at: The insert policy only checked that you were signed in, so any student could book under someone else's email. Fixed in migration 21; the replay shows both.

Numo

closed source numo.gif

about: Local-first statistics app: the stats engine runs on your machine and your data never leaves it. In development.
parts: tauri, python, typescript