AI Agent · earendil.com
What Is a Harness?
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Since then, there has been an encouraging growth of free open source agent harnesses like OpenClaw, OpenCode, Hermes and Pi.
Key facts
- Most famously, Claude Opus 4.5 had a widely publicized “ soul document ” that explained to the AI model what it was and how it should act
- Pi users have shared more than 5,000 extensions with one another
- The System Prompt in an AI harness is similar to this but is less embedded into the model
- Agent harnesses use AI models to create AI agents, and their first application was for coding
Summary
Harness, definition by the Cambridge Dictionary. Noun. a piece of equipment with straps and belts, used to control or hold in place a person, animal, or object. Verb. to control something, usually to use its power. When the reporter thinks of a harness, the reporter thinks first of the set of straps and belts that the reporter put on in middle school before scrambling up the walls of their school. If you’re main-lining into the AI newsfeed these days however, your archetypal harness may already be an agent harness.