This distinction matters. Most people think "Claude Code" is one thing. It's actually two things:
1. The Agent → The AI model that reads, writes, and reasons
2. The Harness → Everything that surrounds the agent:
rules, hooks, commands, subagents, MCPs
The agent is the brain. The harness is the operating system it runs inside. A smarter brain doesn't fix a broken operating system. A better harness makes any brain dramatically more effective.
Rex — What Is an Agent Harness?
This distinction matters. Most people think "Claude Code" is one thing. It's actually two things:
1. The Agent → The AI model that reads, writes, and reasons
2. The Harness → Everything that surrounds the agent:
rules, hooks, commands, subagents, MCPs
The agent is the brain. The harness is the operating system it runs inside. A smarter brain doesn't fix a broken operating system. A better harness makes any brain dramatically more effective.