# Tool Use + Function Calling: LLM's Doors to External World — From OpenAI Tools to MCP

> Source: https://sukruyusufkaya.com/en/learn/llm-muhendisligi/tool-use-function-calling-mcp
> Updated: 2026-05-13T12:42:29.037Z
> Category: LLM Mühendisliği
> Module: Module 20: AI Agents + Tool Use + MCP
**TLDR:** Tool Use anatomy: LLM reading JSON schema tool definitions, choosing right tool with right parameters. OpenAI function calling (June 2023), Anthropic MCP (Model Context Protocol, Nov 2024), Llama-3 tool tokens. Production agent patterns: ReAct, Plan-and-Execute, Reflexion. Turkish agent practice.