| # Concept: Function Calling & Tool Use | |
| ## Overview | |
| Function calling transforms LLMs from text generators into agents that can take actions and interact with the world. | |
| ## What Makes an Agent? | |
| ``` | |
| Text Generator Agent | |
| ────────────── ────── | |
| LLM → Text only LLM + Tools → Can act | |
| ``` | |
| **Function calling** lets the LLM invoke predefined functions to access data or perform actions it cannot do alone. | |
| ## The Core Idea | |
| ``` | |
| User: "What time is it?" | |
| ↓ | |
| LLM thinks: "I need current time" | |
| ↓ | |
| LLM calls: getCurrentTime() | |
| ↓ | |
| Tool returns: "1:46:36 PM" | |
| ↓ | |
| LLM responds: "It's 13:46" | |
| ``` | |
| This is agency - the ability to DO, not just SAY. | |
| ## How It Works | |
| ### 1. Function Definition | |
| ```javascript | |
| getCurrentTime = { | |
| description: "Get the current time", | |
| handler: () => new Date().toLocaleTimeString() | |
| } | |
| ``` | |
| ### 2. LLM Sees Available Tools | |
| ``` | |
| Available functions: | |
| - getCurrentTime: "Get the current time" | |
| - getWeather: "Get weather for a city" | |
| - calculate: "Perform math" | |
| ``` | |
| ### 3. LLM Decides When to Use | |
| ``` | |
| "What time?" → getCurrentTime() ✓ | |
| "What's 5+5?" → calculate() ✓ | |
| "Tell a joke" → No tool needed | |
| ``` | |
| ## Real-World Applications | |
| **Personal Assistant**: Calendar, email, reminders | |
| **Research Agent**: Web search, document reading | |
| **Coding Assistant**: File operations, code execution | |
| **Data Analyst**: Database queries, calculations | |
| ## Key Takeaway | |
| Function calling is THE feature that enables AI agents. Without it, LLMs can only talk. With it, they can act. | |
| This is the foundation of all modern agent systems. | |