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    Web Development

    How to Build an LLM-Powered App in Next.js (2025 Guide)

    4/18/2025
    Mehebub Alam
    319
    How to Build an LLM-Powered App in Next.js (2025 Guide)

    Large Language Models (LLMs) like OpenAI's GPT-4 and Mistral have revolutionized how developers build intelligent applications. Whether you're creating a chatbot, code assistant, or content generator, integrating LLMs into your Next.js project is easier than ever in 2025. In this guide, we’ll walk you through how to create an LLM-powered app using Next.js, with API routes, edge functions, and server-side streaming—all with best practices in mind.

    🧠 How to Build an LLM-Powered App in Next.js (2025 Guide)


    ✨ Introduction

    Large Language Models (LLMs) like OpenAI's GPT-4 and Mistral are transforming how we build apps. From chatbots to content generators, integrating LLMs into your Next.js project is easier than ever in 2025.

    🛠️ Why Use Next.js for LLM Apps?

    • Supports serverless and edge functions
    • Full-stack flexibility (API + frontend)
    • Built-in SSR, SSG, and streaming
    • Great DX with App Router and RSC

    📦 Prerequisites

    • Node.js 18+
    • Next.js app: npx create-next-app@latest
    • OpenAI API key
    • Basic React knowledge

    🧱 Folder Structure Example

    /app
      /chat
        page.tsx           → Chat UI
    /api
      /chat
        route.ts           → LLM API handler

    🔌 Setting Up the LLM API Route

    // /app/api/chat/route.ts
    import { NextResponse } from 'next/server'
    
    export async function POST(req: Request) {
      const { messages } = await req.json()
    
      const response = await fetch('https://api.openai.com/v1/chat/completions', {
        method: 'POST',
        headers: {
          'Content-Type': 'application/json',
          Authorization: `Bearer ${process.env.OPENAI_API_KEY}`,
        },
        body: JSON.stringify({
          model: 'gpt-4',
          messages,
          stream: false,
        }),
      })
    
      const data = await response.json()
      return NextResponse.json({ reply: data.choices[0].message.content })
    }
    💡 Tip: For best performance, set runtime: 'edge'

    💬 Building the Frontend Chat UI

    'use client'
    import { useState } from 'react'
    
    export default function ChatPage() {
      const [messages, setMessages] = useState([{ role: 'user', content: '' }])
      const [input, setInput] = useState('')
    
      const sendMessage = async () => {
        const updatedMessages = [...messages, { role: 'user', content: input }]
        setMessages(updatedMessages)
        setInput('')
    
        const res = await fetch('/api/chat', {
          method: 'POST',
          body: JSON.stringify({ messages: updatedMessages }),
        })
    
        const data = await res.json()
        setMessages([...updatedMessages, { role: 'assistant', content: data.reply }])
      }
    
      return (
        <div className="p-4 max-w-xl mx-auto">
          {messages.map((m, i) => (
            <p key={i}><strong>{m.role}:</strong> {m.content}</p>
          ))}
          <input
            className="border p-2 w-full mt-4"
            value={input}
            onChange={(e) => setInput(e.target.value)}
            onKeyDown={(e) => e.key === 'Enter' && sendMessage()}
            placeholder="Type a message..."
          />
        </div>
      )
    }

    🚀 Going Further

    • Streaming with ReadableStreams
    • Use Pinecone or Weaviate for RAG
    • Add auth via NextAuth.js
    • Store chats in PostgreSQL or MongoDB
    • Deploy with Vercel

    🔐 Example .env

    OPENAI_API_KEY=sk-...

    🌎 Deploying to Production

    Run the following command to deploy:

    vercel

    Set your environment variables in the Vercel dashboard first.

    🧠 Final Thoughts

    With LLMs and Next.js, you're not just building apps — you're crafting intelligent tools that think, assist, and create.

    Build the future with code. 🚀


    Tags:

    GPT-4
    Vercel
    Full Stack
    Edge Functions
    TypeScript
    NextJS
    AI Integration
    Serverless
    App Router
    Chatbot
    React
    Mistral
    Web Development
    OpenAI
    LLM
    AI App
    Mehebub Alam

    Mehebub Alam

    Author

    319

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