# Function Calling

> Function calling is the specific implementation of tool use where the language model emits a structured JSON object matching a function signature, which the host application then executes.

Category: Architecture
Source: https://impetora.com/glossary/function-calling
Part of: Impetora AI consulting glossary (https://impetora.com/glossary)

## What is Function Calling?

Function calling is the dominant API pattern for tool use across major model providers. The developer registers function schemas; the model returns a function name and arguments; the application validates and executes them; the result is fed back to the model. Function calling allows strict schema enforcement, type validation, and clean separation between model output and side effects. It is the safest way to let an LLM trigger real-world actions.

## How does Function Calling apply to enterprise AI?

Function calling is used in enterprise voice agents, customer support automation, internal copilots, and any workflow where AI must read or write to a system of record.

## Related terms

- [Tool Use](https://impetora.com/glossary/tool-use) - Tool use is the capability of a language model to invoke external functions, APIs, or services as part of producing a response.
- [Agentic AI](https://impetora.com/glossary/agentic-ai) - Agentic AI refers to systems that plan multi-step actions, call external tools, and operate with some autonomy toward a goal, rather than producing a single response to a single prompt.
- [Guardrails](https://impetora.com/glossary/guardrails) - Guardrails are runtime checks placed around an AI system to constrain inputs, outputs, and tool calls within safety, compliance, and business policy.
- [Prompt Engineering](https://impetora.com/glossary/prompt-engineering) - Prompt engineering is the practice of designing, testing, and versioning the instructions given to a language model to elicit reliable, evaluable outputs.

## External references

- [OpenAI function calling](https://platform.openai.com/docs/guides/function-calling)

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