LangChain.js Has a Free AI Framework: Build LLM-Powered Apps With Chains, Agents, and RAG in TypeScript

You want to build an AI app that searches your documents, calls APIs, and reasons through multi-step problems. The OpenAI SDK gives you chat completions. But chaining prompts, managing context windows, vectorizing documents, and building agent loops? That's on you. LangChain.js gives you composable building blocks — chains, agents, retrievers, memory — for building complex AI applications. Quick Start npm install langchain @langchain/openai Basic Chain import { ChatOpenAI } from " @langchain/openai " ; import { ChatPromptTemplate } from " @langchain/core/prompts " ; import { StringOutputParser } from " @langchain/core/output_parsers " ; const model = new ChatOpenAI ({ modelName : " gpt-4-turbo " }); const prompt = ChatPromptTemplate . fromMessages ([ [ " system " , " You are a technical writer. Write concise explanations. " ], [ " user " , " Explain {topic} in 3 sentences for {audience}. " ], ]); const chain = prompt . pipe ( model ). pipe ( new StringOutputParser ()); const result = a