An AI calling outside tools, like a calculator, search or code, to get things right.
Language models are built to continue text, so they're shaky at exact math and at anything new, like today's weather. The fix is to give them tools: a calculator, web search, a code runner, a calendar.
The model doesn't run the tool itself. It writes a request in a set format, like "call the calculator with these numbers"; the app runs it and hands back the result, which the model uses to finish its answer. After OpenAI launched function calling in 2023, this became a standard feature of major AI services.
The real skill is knowing when to reach for a tool. Meta's 2023 Toolformer study taught a model to decide that by itself.
Think of it like this
On a test where calculators are allowed, the smart move on a giant multiplication isn't mental math; it's grabbing the calculator. Tool use is an AI making that same call.
For example
Ask "What's 1,234 × 5,678?" and a good AI calls a calculator instead of guessing.
Records about this
Source-checked moments from AI history.
Tool calling was promoted from prompt parsing to a structured JSON-schema interface; the de facto standard API for agent development
Learns on its own, through self-supervised learning, when to call APIs and with what arguments — the route of building tool use into the weights