tropo

The Agentic Builders / New to Agents · 6 of 14

What is a Harness

· 3 min read

New to Agents · Beginner Path · 6 of 14

The LLM is the brain. The harness is the body - and without it, the brain just talks.

An LLM on its own can only produce text. It cannot open a file, run a command, search the web, or even take a second turn. The harness is the program wrapped around the model that gives it those abilities. It is the loop and the hands.

Concretely, a harness does three jobs:

  • Tools. It gives the model a set of actions it can call, and it actually runs them when the model asks.
  • The loop. It feeds the model the situation, lets it decide on an action, performs that action, feeds the result back, and repeats - turning a one-shot answer into ongoing work.
  • Access. It controls what the model can see and touch: which files, which commands, what's off-limits.

Claude Code is a harness: it's what lets the Claude model actually read your repository and edit files, instead of just describing what it would do. Change the harness and you change what the same model can accomplish. The brain stays the same; the body is what makes it an agent.

The harness is the body around the brain LLM ALONE LLM just text can describe, can't do LLM IN A HARNESS HARNESS · tools · loop · access LLM reads files · runs commands · searches Same model. The harness is what turns "would do" into "did."

Why this matters for Tropo

The harness is the one part of the stack Tropo deliberately does not replace. Tropo rides on top of whatever harness you use - Claude Code today, others tomorrow.

That's the point. Tropo is just markdown files in a folder, so it works in any harness that can read files. The harness gives your agent hands; Tropo gives it a memory, a method, and a crew - without chaining you to one vendor's hands. If a better harness comes along, your vault moves with you.

Beginner Path · New to Agents ← Before: What is a Session · Next: What is a Tool or Skill → Related: What is an Agent · See the whole path: New to Agents - Beginner Path