ReAct

This walkthrough showcases using an agent to implement the ReAct logic.

Setup

Install the OpenAI integration package, retrieve your key, and store it as an environment variable named OPENAI_API_KEY:

tip

See this section for general instructions on installing integration packages.

npm

npm install @langchain/openai

Yarn

yarn add @langchain/openai

pnpm

pnpm add @langchain/openai

This demo also uses Tavily, but you can also swap in another built in tool. You'll need to sign up for an API key and set it as TAVILY_API_KEY.

Initialize Tools

We will first create a tool:

import { TavilySearchResults } from "@langchain/community/tools/tavily_search";

// Define the tools the agent will have access to.
const tools = [new TavilySearchResults({ maxResults: 1 })];

Create Agent

import { AgentExecutor, createReactAgent } from "langchain/agents";
import { pull } from "langchain/hub";
import { OpenAI } from "@langchain/openai";
import type { PromptTemplate } from "@langchain/core/prompts";

// Get the prompt to use - you can modify this!
// If you want to see the prompt in full, you can at:
// https://smith.langchain.com/hub/hwchase17/react
const prompt = await pull<PromptTemplate>("hwchase17/react");

const llm = new OpenAI({
  model: "gpt-3.5-turbo-instruct",
  temperature: 0,
});

const agent = await createReactAgent({
  llm,
  tools,
  prompt,
});

Run Agent

Now, let's run our agent!

tip

LangSmith trace

const agentExecutor = new AgentExecutor({
  agent,
  tools,
});

const result = await agentExecutor.invoke({
  input: "what is LangChain?",
});

console.log(result);

/*
  {
    input: 'what is LangChain?',
    output: 'LangChain is a platform for building applications using LLMs (Language Model Microservices) through composability. It can be used for tasks such as retrieval augmented generation, analyzing structured data, and creating chatbots.'
  }
*/

Using with chat history

For more details, see this section of the agent quickstart.

// Get the prompt to use - you can modify this!
// If you want to see the prompt in full, you can at:
// https://smith.langchain.com/hub/hwchase17/react-chat
const promptWithChat = await pull<PromptTemplate>("hwchase17/react-chat");

const agentWithChat = await createReactAgent({
  llm,
  tools,
  prompt: promptWithChat,
});

const agentExecutorWithChat = new AgentExecutor({
  agent: agentWithChat,
  tools,
});

const result2 = await agentExecutorWithChat.invoke({
  input: "what's my name?",
  // Notice that chat_history is a string, since this prompt is aimed at LLMs, not chat models
  chat_history: "Human: Hi! My name is Cob\nAI: Hello Cob! Nice to meet you",
});

console.log(result2);

/*
  {
    input: "what's my name?",
    chat_history: 'Human: Hi! My name is Cob\nAI: Hello Cob! Nice to meet you',
    output: 'Your name is Cob.'
  }
*/