Harness Engineering
Improving an AI agent by changing what surrounds the model instead of the model itself: clearer instructions, better tools, written-down state, checks that prove the work is done, and permissions. The working habit is that each time the agent makes a mistake, you change the Agent Harness so it cannot make that mistake again. Harness engineering overlaps with Context Engineering, which covers what goes into the context window on each turn.
Written by Max Zeshut
Founder at Agentmelt · Last updated Oct 26, 2026
Example
A coding agent keeps declaring features finished while tests fail. Instead of moving to a larger model, the team adds a definition of done the agent must check by command (tests pass, types check) and a progress file the next session reads first. The false 'done' reports stop.
Frequently asked questions
- Where should I start with harness engineering?
- With one short instruction file at the root of the project (AGENTS.md or CLAUDE.md) that names the stack, the conventions and the commands that prove the work. Then log each failure against one of five layers (task, context, environment, verification, state) and fix the layer that breaks most often.