Harness Engineering
The practice of designing, testing, and simplifying the runtime around an agent so it can work reliably across tools, sessions, and tasks.
Plain English
It is systems engineering for the part around the model: context, tools, permissions, state, loops, and evaluation.
Example
A team improves a coding agent by adding sprint contracts, a QA evaluator, Playwright checks, and then removing pieces once a newer model no longer needs them.
Why it matters
Recent agent gains often come from better runtime structure, not only from larger models or better prompts.