---
title: "The harness is not the model"
lesson_id: "01"
---

# The harness is not the model

- **Lesson ID:** 01
- **Goal:** Define the harness as everything around the model. An agent is a controlled workflow. The model is swappable.
- **Human lesson:** [01-harness-not-the-model.html](01-harness-not-the-model.html)

## Prerequisites

- A feature the reader can describe as "the model answers, then the app acts."

## Inputs, outputs, and artifacts

- **Inputs:** The habit of treating a new model as a new product.
- **Outputs:** A recipe: instructions, scoped context, tools, verifier, guardrails.
- **Artifacts:** One small Mermaid diagram of question to harness to model to checked answer.

## Agent build steps

1. Say the harness wraps the model. The model writes tokens. The harness owns context, tools, checks, and when a person steps in.
2. Say an agent is a controlled workflow: trusted context, bounded tools, evaluation, human judgment, and ops ownership.
3. Say the model is the smallest, swappable part.
4. List the recipe: instructions + scoped context + tools + verifier + guardrails.
5. Walk a research agent: confirm who asked, plan, approved data, trusted calc, cite, stop if confidence is low.
6. Draw a small Mermaid diagram: Question → Harness → Model → Harness → Checked answer.
7. Link the context packer and guardrails courses.

## Constraints

Keep the language simple, friendly, and literal. No quizzes, no em dashes, no invented WWDC sessions. Do not repeat the X post link. Brand Edge FDE only.

## Key concepts

- The harness is everything wrapped around the model.
- An agent is a controlled workflow: trusted context, bounded tools, evaluation, human judgment, and ops ownership.
- The model is the smallest part. You should be able to swap it.
- The recipe is instructions, scoped context, tools, a verifier, and guardrails.
- A research agent confirms who asked, plans, reads approved data, uses a trusted calc, cites evidence, and stops when confidence is low.

## Takeaways

- Do not treat a new model as a new product. Change the harness first.
- If a model swap rewrites the app, the rules were stuck inside prompts or call sites.
- Write the recipe in software you own: context pack, tools, verifier, guardrails.

## Acceptance checks

- Harness vs model is the main claim.
- Recipe and research-agent checks are present.
- Small Mermaid diagram and Agent brief link are present.
- [ ] Proceed to [lesson 02 brief](02-six-layers.llms.md).