Everyone is talking about AI harnesses right now.
But what is a harness actually?
Simple way to think about it:
The model is the brain.
The harness is everything around the model that helps it do useful work.
A raw LLM can write, reason, explain, and code.
But an AI agent needs more than that.
It needs context.
It needs tools.
It needs memory.
It needs permissions.
It needs workflows.
It needs evals and feedback loops.
That surrounding layer is the harness.
And this is why two agent products using the same model can feel completely different.
One agent feels confused.
It loads too much context, calls the wrong tool, burns tokens, and loses the task halfway.
Another agent feels sharp.
It finds the right context, uses the right tools, remembers what matters, asks for approval when needed, and finishes reliably.
Same model.
Different harness.
Big difference.
It is the execution layer that turns model intelligence into actual work.