# Harness

> A course in building software with agents, from nothing: 526 terms, most with an instrument you can operate. Use it to name what someone describes and to write precise briefs.

- [Full glossary as Markdown](https://dev.dqnotes.com/glossary.md)
- [Agent skill: reverse-lookup glossary](https://dev.dqnotes.com/skills/agentic-engineering-vocabulary/SKILL.md)
- [Receipts: every check that ran on this site](https://dev.dqnotes.com/receipts)
- [The experiment: what we measured and what it does not show](https://dev.dqnotes.com/experiment)

## Chapters

- [The machine](https://dev.dqnotes.com/machine): What a program is and what happens when one runs, from the first line of code to the terminal.
- [The network](https://dev.dqnotes.com/network): How a web app works: browsers, servers, requests, databases, and what happens between them.
- [Version control](https://dev.dqnotes.com/git): Commits, branches, diffs and pull requests: the undo button and the paper trail for everything an agent does.
- [Reading and debugging](https://dev.dqnotes.com/reading): How to read code you did not write, and how to find a bug when the agent has run out of ideas.
- [The model](https://dev.dqnotes.com/model): What a language model is and is not: tokens, context, sampling, tools, cost, and why it sounds sure when it is wrong.
- [The agent](https://dev.dqnotes.com/agent): A model plus a loop plus tools. Everything around the model is the harness, and that part is yours.
- [Context](https://dev.dqnotes.com/context): What the agent can see decides what it can do. How to feed it, keep it clean, and carry knowledge between sessions.
- [The brief](https://dev.dqnotes.com/brief): How to say what you want: specs, acceptance criteria, plans, slices, and the questions to ask first.
- [Backpressure](https://dev.dqnotes.com/backpressure): Checks that say no. Types, linters, hooks and gates that reject bad work before you ever see it.
- [Tests](https://dev.dqnotes.com/tests): What a test proves and what it does not, from a first unit test to mutation testing and hidden scenarios.
- [Design](https://dev.dqnotes.com/design): What makes code good to change: naming, coupling, complexity, refactoring, and how slop gets in.
- [Review](https://dev.dqnotes.com/review): Reading a diff for what matters, using a second agent well, and owning what you merge.
- [Security](https://dev.dqnotes.com/security): Injection, secrets, access control, supply chains, and the new attacks that target the agent itself.
- [Data and failure](https://dev.dqnotes.com/data): Databases, transactions, migrations, concurrency and retries: the failures that only show up in production.
- [Performance and cost](https://dev.dqnotes.com/performance): How to measure speed honestly, where time goes, and what tokens cost.
- [Shipping and running](https://dev.dqnotes.com/ship): Getting code to users safely and knowing what it does there: deploys, flags, rollbacks, logs and incidents.
- [Many agents](https://dev.dqnotes.com/many): Parallel work, roles, handoffs, loops, evals and factories: running a team that never sleeps and never remembers.
- [The proof](https://dev.dqnotes.com/proof): What the evidence really says, what to claim, and how to show it to someone who is paid to doubt you.