The Harness Engineering Book
The complete knowledge base behind Vizuara's Harness Engineering — 35 illustrated chapters that build a coding-agent harness from scratch, in the spirit of pi. Each is written from first principles and cross-linked to the chapters it needs. Start anywhere.
How to read this book →The thesis. Why a model alone is not an agent, the precise difference between prompt, context, and harness engineering, and the five layers you will build across the workshop into your own coding harness.
Day 1. The beating heart of every harness: a loop that calls the model, runs the tools it asks for, and repeats until the work is done. We build a bare harness from first principles.
Day 2. A harness that can only talk is a chatbot. We give it hands: file and shell tools with strict schemas, permission gates before dangerous actions, and a sandbox to contain the blast radius.
Day 3. The context window is the scarcest resource in the system. We build the machinery that decides what the model sees every turn, compacts long sessions, and remembers across them.
Day 4. Real agents crash, get interrupted, and hit jobs too big for one context. We make the harness recoverable and self-healing, and teach it to dispatch sub-agents under supervision.
Day 5. We dissect three real harnesses to see how they implement, at scale, everything you just built by hand, then you assemble your own and demo it.