Tool Call

What is a Tool Call

A tool call is one specific invocation of a tool: the model requesting to read this exact file, run this exact command, search for this exact term, with real arguments filled in. It is distinct from the tool itself, which is the general capability, a tool call is one concrete use of it, made once, with a specific result.

A single turn can involve several tool calls in sequence, the model reading a file, checking a result, then deciding to read a second file before finally answering. Each call is executed by the harness, not by the model directly, and its result is fed back into context as the basis for whatever the model does next in that same turn.

A tool call is not guaranteed to succeed just because the model made it, arguments can be malformed, a file can be missing, a command can fail. The harness surfaces that failure back to the model the same way it would surface a success, as a result the model then has to reason about and often correct.