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Harness Engineering — Make Your Coding Agent Better Without Changing the Model
How runtime context, guardrails, and feedback loops make coding agents more reliable.
If you’ve been using Claude Code, Codex, or Cursor for a while, you’ve probably encountered situations like these.
You ask an agent to implement a feature. It writes the code. Everything looks fine. Then you notice it hasn’t run a single test. Or it refactors a few unrelated files even though you asked it to keep the changes minimal.
Sometimes it gets stuck fixing the same error over and over. You interrupt it, explain what’s wrong, and ask it to try something different.
That fixes the current problem. Start a new session, though, and the same mistake can happen again.
You can keep adding instructions to CLAUDE.md or AGENTS.md. That helps, but only up to a point.
What if you could control how the agent runs commands? What if you could check its work, spot loops, and recover from failures without stepping in every time?
That’s what harness engineering is about.
We’ll start with the basics, break down the parts of a harness, then build a few mechanisms that make coding agents more reliable.
