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Plain-English definition

Function Calling

In one breath

How a model asks other software to do something for it — run a search, check a calendar, send an email — instead of just describing it in words. The plumbing behind agentic AI.

In more detail

Function calling is how an AI asks other software to do something. Instead of describing an action in words, the model emits a structured request — check the weather here, search these flights, add this to the calendar — and the connected app runs it and hands back the result.

It matters because it’s the bridge from talking to doing. A model on its own can only write about booking a table; with function calling it can actually trigger the booking. It’s the basic plumbing underneath agentic AI, and the mechanism that standards like MCP make universal.

📌 See it in action

You ask, ‘Will it rain in Paris tomorrow? If not, book my usual bistro.’ The model can’t know the weather or make reservations by itself — so it calls a weather function, reads back ‘clear skies,’ then calls the reservation function. You get one tidy reply: ‘Sunny — table for two booked at eight.’

Goes with
Agentic AI →MCP (Model Context Protocol) →Computer Use →

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