Phase 4: Harness Engineering · 50 min · Claude Code · Python
Building a Harness for Your Product
The harness gets a spec too — the same discipline you applied to the product in phases 0–3, now applied to how the agent is allowed to build it.
Real-world application: A written harness spec — not just an implemented harness — is evidence you can communicate agent-safety and reliability decisions to a team, which is exactly what a lead or senior engineer is expected to produce.
What you will learn
- Distinguish a product spec (what the product does) from a harness spec (how the agent is allowed to build and maintain it)
- Design concrete decisions for each of the six harness components for a real product
- Justify a tool-access decision based on what the product actually touches (e.g. user-uploaded files, payment data)
- Generate and validate a harness specification document for your course-long product
Introduction
Building a Harness for Your Product
Objective
Generate a HARNESS.md document from structured per-component decisions and validate that every section contains a substantive, product-specific decision rather than generic policy language.
Unlock the full lesson
You've read the first 2 sections. The rest of this lesson covers The Problem, The Concept, Build, Check Yourself, Key Terms & Next — plus a hands-on lab, quiz, and project artifact.
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