How Agent Tool Calling Works

The basic loop

A model proposes a tool and arguments; the application validates, authorizes, executes, and returns a structured result. The model never directly runs application code.

• Select
• Validate
• Execute
• Observe
• Continue or stop

Where reliability comes from

Reliability lives in the orchestration layer: typed arguments, timeouts, idempotency, permission boundaries, and a bounded retry policy.

• Reject unknown tools
• Record every transition
• Separate retryable from terminal failures

A useful design rule

Let the model decide what may be useful, but let deterministic code decide what is allowed and whether the result is valid.