No prerequisites. If you've used Claude or ChatGPT and you're wondering what separates a one-off script from an agent that actually runs in production, this post is for you. I wrote my first Python agent in April 2026. It did two things: read a PDF, send a Telegram message. It worked. Once. The second time, the PDF was poorly scanned. The agent crashed. No trace. No notification. The patient never got their appointment. That's the day I understood: an agent that works in demo is not an agent. An agent is what holds up when you're not around. I wrote four words in the docstring of my next agent: Observability, Reliability, Security, Deployment. Since then, I haven't shipped a single agent to production without all four. Today I run about twenty of them, 24/7, on a single 5€/month server. Here they are, with the Python code that incarnates them. Pillar 1 — Observability You must be able to know, without asking anyone: what the agent did, when, how long it took, and how much it cost.…