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Harness Engineering

The instructor has published 80% of this course.Last updated on 2026-07-29

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About

About

About the Course

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Instructor

About the Instructor

Ian Johnson

Ian Johnson is a staff engineer at Parento, where he runs the engineering team's adoption of AI coding agents and the harness work that keeps that adoption from breaking in production. He owns Huckleberry, a small consultancy that helps engineering teams make AI-generated code shippable. He wrote Keystone, an open-source binary that scaffolds an opinionated harness into any repo in one command, then gets out of the way and leaves markdown the team can edit. Three earlier tools — Bridle, Sellier, and intent-driven-delivery — preceded Keystone, each one shipped publicly, each one teaching a specific lesson the book consolidates. He has been writing about this work at blog.tacoda.dev since 2024, with fifteen-plus long-form posts behind it. He lives outside Austin with his family.

Material

Course Material

  • Everything Around the Agent

  • What you build

  • How to take this course

  • Foundations

  • The Agent Is Already in Your Codebase

  • Determinism Is the Wrong Goal

  • The Boundary: Authored vs Applied

  • Five Disciplines People Keep Confusing

  • Placing the five disciplines

    2 attempts allowed

  • The Repo Teaches the Agent Three Ways

  • Charter Engineering

  • CLAUDE.md: The Front Door

  • Implementation

  • Rule Files, and the Rules About Rules

  • Implementation

  • Guides and the Example the Agent Copies

  • Implementation

  • Where Charter Lives, and What the Agent Remembers

  • Implementation

  • The Code Is Charter Too

  • Implementation

  • Boring Code and Tests the Agent Can Run

  • Implementation

  • Tools and Permissions: Bounding What the Agent Can Do

  • Implementation

  • Hooks: Deterministic Automation on an Event

  • Implementation

  • Slash Commands: A Saved Prompt You Invoke by Name

  • Implementation

  • Skills: A Capability the Model Reaches For

  • Implementation

  • Subagents: A Specialized Worker in Its Own Context

  • Implementation

  • MCP Servers: Capability From Outside the Agent

  • Implementation

  • Plugins and Marketplaces: Charter You Distribute

  • Implementation

  • Contracts, Phases, and Gates

  • Implementation

  • Keeping the Charter Alive

  • Implementation

  • Capstone: a charter that runs

  • Charter, checked

    2 attempts allowed

  • Harness Engineering

  • The Harness, Defined

  • In code

  • When You Actually Need a Harness

  • In code

  • Inherit the Agent, Configure the Difference

  • In code

  • Force the Output Into a Shape You Can Check

  • In code

  • What the Model Sees Each Turn

  • In code

  • Building Tools: An MCP Server From First Principles

  • In code

  • The boundary

  • Every Tool Is Unsupervised Power

  • In code

  • Verification Is a Node, Not a Question

  • In code

  • Test the Harness Like the Code It Is

  • In code

  • Capstone: the mender, wired

  • Harness, checked

    2 attempts allowed

  • Graph Engineering

  • The Thing That Decides What Runs Next

  • In code

  • Control Flow as a Graph

  • In code

  • Two Shapes: The Pipeline and the Loop

  • Pick the shape

    2 attempts allowed

  • Running the Phases, and Asking for a Human

  • When One Agent Is Not Enough

  • The Factory

  • The Loop That Spends Money

  • In code

  • A Factory Is a Distributed System

  • In code

  • You Cannot Watch It, So Instrument It

  • In code

  • Ship It: The Factory, Assembled

  • Capstone: the mending factory

  • In code

  • The factory, checked

    2 attempts allowed

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