AI Glossary / Core concepts
Agent harness.
Also known as: harness, wrapper
The harness is the app wrapped around a model that gives it tools, memory, and the ability to act. The model is the brain; the harness is everything that turns that brain into something that gets work done. A model is only as good as its harness, the place where you use it.
The cleanest way to think about it is cars. Claude Code is a Ferrari, Codex is a G-Wagon, Spark is a Range Rover. Different vehicles, but once you learn the steering, the brakes, and the ignition in one (your context, your Skills, your MCP (Model Context Protocol)) you can hop in any other and drive it.
That's why the harness matters as much as the model, and why it pays to get good at one. The skills transfer. When a better model drops next month, you swap it into the same harness and keep everything you've built around it.