How LLMs Use Tools | Tool Binding & Tool Calling in LangChain Explained | @SCALER

Your LLM is smart, but it can't book a flight, check the weather, or run a search on its own. That's where tools come in. In this session, we break down how LLMs interact with external tools — what tool binding actually means, how tool calling works step by step, and why the LLM isn't the one executing anything. We build this from scratch with real code so you can see exactly what's happening under the hood. What a tool actually is in LangChain (and why it's just a Python function) The difference between tool binding and tool execution How the LLM suggests a tool and generates inputs — without running it Building a custom tool with Pydantic schema enforcement Chaining two tools together: geocoding + live weather via Open-Meteo API How message history must be structured for multi-tool calls to work Why this manual process is the foundation for agents (coming next) By the end, you'll have built a working two-tool pipeline and understand exactly why agents are the next step. Who this is for: - Engineers building with LLMs who want real control over tool use - Anyone moving from basic prompting to agentic workflows - Developers who want to understand what's happening before using agent frameworks. ### In this video, you'll learn: ✔ What is an LLM and why it can't execute tasks ✔ What is a Tool in LangChain ✔ What is Tool Binding ✔ Tool in LangChain is a Runnable ✔ How LLM responds with a Tool Call ✔ Implementing an Inbuilt Tool (DuckDuckGo Search) ✔ Creating a Custom Tool with Refund Tool Test Bot decorator ✔ Tool Binding with LLM ✔ Building a Full Application with Tool Calling ✔ Tool 1: Get Latitude & Longitude (Open-Meteo API) 🎓 Join a FREE live masterclass: https://www.scaler.com/events/?utm_source=youtube&utm_medium=description&utm_content=QBP456x2kRY ⏱ Chapters: 00:00 Introduction to Agents & Tools 00:42 What is an LLM and why it can't execute tasks 03:18 What is a Tool in LangChain 05:18 What is Tool Binding 07:48 Tool in LangChain is a Runnable 09:20 Ho