15 · The Workbench
Harness
Agent harness / workbench
Everything wrapped around a model that turns chat into action: what context it reads, which tools it can call, where code runs, how instructions persist, what you must approve, and how work gets verified. Cursor, Claude Code, and Codex are harnesses — not models.
Concrete example
The same Claude model in a browser chat vs a terminal agent with shell access are radically different products because the harness differs.
Why it matters
The layer that actually matters when you are picking tools.