Definition
Plain language
A structured request an AI agent makes to use an external function or service.
As stated in the literature
A structured invocation issued by an LLM agent to call an external function, tool, or API, whose result is fed back into the model's context.
Also called: tool calls, tool use
Why it matters: Tool calls are how LLMs reach beyond their training data to take real actions, and their correctness is central to every agent's reliability.
For example, an agent answering 'what's the weather in Tokyo' issues a tool call to a weather API with city='Tokyo' and uses the returned JSON to compose its reply.
Heard on the show
“A company file, discoverable through normal tool use.”Episode 001 — When AI Models Quietly Protect Each Other From Shutdown