Tool

A function the harness exposes for the agent to call — Read, Write, Bash, Search. Tools are how an agent perceives and acts on the environment: it can't see the environment except through tool results, and can't change it except through tool calls. Each tool call costs an extra model provider request, since the result has to go back to the model before it can decide what to do next.

Usage:

"Can the agent query staging directly?"

"Add a psql tool to the harness, scoped read-only on staging. Without a tool for it, the agent's blind to anything outside the filesystem."