James' Growth Diary

Apr 9, 2026 · Artificial Intelligence

Building a Tool-Calling Agent from Scratch with LangChain.js

This tutorial walks through creating a fully functional Tool-Calling Agent using LangChain.js, covering tool definition, model binding, manual execution loops, the high‑level createReactAgent API, streaming responses, state management with thread IDs, common pitfalls, and a complete runnable example.