Harness vs Prompting Question Explained
This worked Harness Engineering practice question tests Harness Basics. Try the answer first, then review why C is the best choice.
Short answer
The correct answer is C. Add an AGENTS.md rule or a check that fails with no footer.
Mitchell Hashimoto describes harness engineering as a habit. Each time the agent makes a mistake, you engineer a solution so the agent never makes that mistake again. He lists two forms of fix: better instructions in AGENTS.md, and programmed tools that report the agent's errors back to it. The same footer removed three times is the signal to add one of those, not to type a fourth correction. The correct answer is C. Add an AGENTS.md rule or a check that fails with no footer
The Question
Your agent has removed the footer by accident three times in one week. Each time you asked it to put the footer back. Which next step is harness engineering, rather than more prompting?
Why C is correct
Mitchell Hashimoto describes harness engineering as a habit. Each time the agent makes a mistake, you engineer a solution so the agent never makes that mistake again. He lists two forms of fix: better instructions in AGENTS.md, and programmed tools that report the agent's errors back to it. The same footer removed three times is the signal to add one of those, not to type a fourth correction. The correct answer is C. Add an AGENTS.md rule or a check that fails with no footer
Why the other options are wrong
Words like "be careful" add no fact and no check. The agent still has nothing that tells it the footer is required or detects its removal.
A different model can make the same mistake, because nothing in the project says the footer must stay. The missing piece is in the harness, not the model.
Pasting history fills the context with old conversation. It does not create a durable rule or a check, and the next new session starts empty again.
Key idea: Harness Basics
Every question here is a situation you meet with Claude Code or Codex: the agent gets something wrong, and you choose what to change. The best answer is usually a file, a check, or a hook that stops the mistake from repeating, not a louder prompt. If you miss a question, read the explanation and note which part of the harness it uses: the AGENTS.md map, a skill, a check, a visitor check, a hook, or a handoff note.
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