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A single agent system involves one autonomous entity that perceives its environment and takes actions to achieve specific goals. It makes decisions independently, without coordination or interaction with other agents.

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Installation

npm i langchain @langchain/openai zod

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Quick Start

Create your first agent: 
import { createAgent } from "langchain";
import { ChatOpenAI } from "@langchain/openai";

const model = new ChatOpenAI({
  model: process.env.OPENAI_MODEL || "gpt-4o-mini",
  apiKey: process.env.OPENAI_API_KEY,
  configuration: {
    baseURL: process.env.OPENAI_BASE_URL,
  },
});

const agent = createAgent({
  model,
});

await agent.invoke({
  messages: [{ role: "user", content: "Hello, how are you?" }],
});

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Adding Tools

Tools extend agent capabilities beyond text generation. 
import { createAgent, tool } from "langchain";
import { ChatOpenAI } from "@langchain/openai";
import * as z from "zod";

const getWeather = tool((input) => `It's always sunny in ${input.city}!`, {
  name: "get_weather",
  description: "Get the weather for a given city",
  schema: z.object({
    city: z.string().describe("The city to get the weather for"),
  }),
});

const model = new ChatOpenAI({
  model: process.env.OPENAI_MODEL || "gpt-4o-mini",
  apiKey: process.env.OPENAI_API_KEY,
  configuration: {
    baseURL: process.env.OPENAI_BASE_URL,
  },
});

const agent = createAgent({
  model,
  tools: [getWeather],
});

await agent.invoke({
  messages: [{ role: "user", content: "What's the weather in Tokyo?" }],
});

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Next Steps