---
type: "Glossary term"
title: "Function calling"
description: "A model emitting a tool invocation against a declared function schema."
tags: [glossary]
generated: { by: human:crpage, at: 2026-07-09T09:44:00Z }
aliases: "function calling; function call; tool calling"
status: stable
---

# Definition
A model generating a tool invocation against a **declared function schema** — a vendor-native abstraction, the bridge from natural language to external systems.

# Used in this bundle
Appears in: [structured-outputs](../standards/structured-outputs.md), [openai](../organisations/openai.md).

# Related terms
[api calling](api-calling.md), [tool use](tool-use.md), [structured output](structured-output.md).