Next.js App Router Quickstart

In this quick start tutorial, you'll build a simple AI-chatbot with a streaming user interface. Along the way, you'll learn key concepts and techniques that are fundamental to using the SDK in your own projects.

Check out Prompt Engineering and HTTP Streaming if you haven't heard of them.

Prerequisites

To follow this quickstart, you'll need:

• Node.js 18+ and pnpm installed on your local development machine.
• An OpenAI API key.

If you haven't obtained your OpenAI API key, you can do so by signing up on the OpenAI website.

Create Your Application

Start by creating a new Next.js application. This command will create a new directory named my-ai-app and set up a basic Next.js application inside it.

pnpm create next-app@latest my-ai-app

Navigate to the newly created directory:

cd my-ai-app

Install dependencies

Install ai and @ai-sdk/openai, the Vercel AI package and Vercel AI SDK's OpenAI provider respectively.

pnpm install ai @ai-sdk/openai zod

Configure OpenAI API key

Create a .env.local file in your project root and add your OpenAI API Key. This key is used to authenticate your application with the OpenAI service.

touch .env.local

Edit the .env.local file:

OPENAI_API_KEY=xxxxxxxxx

Replace xxxxxxxxx with your actual OpenAI API key.

Create a Route Handler

Create a route handler, app/api/chat/route.ts and add the following code:

import { openai } from '@ai-sdk/openai';
import { streamText } from 'ai';

// Allow streaming responses up to 30 seconds
export const maxDuration = 30;

export async function POST(req: Request) {
  const { messages } = await req.json();

  const result = await streamText({
    model: openai('gpt-4-turbo'),
    messages,
  });

  return result.toAIStreamResponse();
}

Let's take a look at what is happening in this code:

1. Define an asynchronous POST request handler and extract messages from the body of the request. The messages variable contains a history of the conversation between you and the chatbot and provides the chatbot with the necessary context to make the next generation.
2. Call streamText, which is imported from the ai package. This function accepts a configuration object that contains a model provider (imported from @ai-sdk/openai) and messages (defined in step 1). You can pass additional settings to further customise the model's behaviour.
3. The streamText function returns a StreamTextResult. This result object contains the toAIStreamResponse function which converts the result to a streamed response object.
4. Finally, return the result to the client to stream the response.

This Route Handler creates a POST request endpoint at /api/chat.

Wire up the UI

Now that you have a Route Handler that can query an LLM, it's time to setup your frontend. Vercel AI SDK's UI package abstracts the complexity of a chat interface into one hook, useChat.

Update your root page (app/page.tsx) with the following code to show a list of chat messages and provide a user message input:

'use client';

import { useChat } from 'ai/react';

export default function Chat() {
  const { messages, input, handleInputChange, handleSubmit } = useChat();
  return (
    <div className="flex flex-col w-full max-w-md py-24 mx-auto stretch">
      {messages.map(m => (
        <div key={m.id} className="whitespace-pre-wrap">
          {m.role === 'user' ? 'User: ' : 'AI: '}
          {m.content}
        </div>
      ))}

      <form onSubmit={handleSubmit}>
        <input
          className="fixed bottom-0 w-full max-w-md p-2 mb-8 border border-gray-300 rounded shadow-xl"
          value={input}
          placeholder="Say something..."
          onChange={handleInputChange}
        />
      </form>
    </div>
  );
}

This page utilizes the useChat hook, which will, by default, use the POST API route you created earlier (/api/chat). The hook provides functions and state for handling user input and form submission. The useChat hook provides multiple utility functions and state variables:

• messages - the current chat messages (an array of objects with id, role, and content properties).
• input - the current value of the user's input field.
• handleInputChange and handleSubmit - functions to handle user interactions (typing into the input field and submitting the form, respectively).
• isLoading - boolean that indicates whether the API request is in progress.

Running Your Application

With that, you have built everything you need for your chatbot! To start your application, use the command:

pnpm run dev

Head to your browser and open http://localhost:3000. You should see an input field. Test it out by entering a message and see the AI chatbot respond in real-time! Vercel AI SDK makes it fast and easy to build AI chat interfaces with Next.js.

Stream Data Alongside Response

Depending on your use case, you may want to stream additional data alongside the model's response. This can be done using StreamData.

Update your Route Handler

Make the following changes to your Route Handler (app/api/chat/route.ts):

import { openai } from '@ai-sdk/openai';
import { streamText, StreamData } from 'ai';

// Allow streaming responses up to 30 seconds
export const maxDuration = 30;

export async function POST(req: Request) {
  const { messages } = await req.json();

  const data = new StreamData();
  data.append({ test: 'value' });

  const result = await streamText({
    model: openai('gpt-4-turbo'),
    messages,
    onFinish() {
      data.close();
    },
  });

  return result.toAIStreamResponse({ data });
}

In this code, you:

1. Create a new instance of StreamData.
2. Append the data you want to stream alongside the model's response.
3. Listen for the onFinish callback on streamText and close the stream data.
4. Pass the data into the toAIStreamResponse method.

Update your frontend

To access this data on the frontend, the useChat hook returns an optional value that stores this data. Update your root route with the following code to render the streamed data:

'use client';

import { useChat } from 'ai/react';

export default function Chat() {
  const { messages, input, handleInputChange, handleSubmit, data } = useChat();
  return (
    <div className="flex flex-col w-full max-w-md py-24 mx-auto stretch">
      {data && <pre>{JSON.stringify(data, null, 2)}</pre>}
      {messages.map(m => (
        <div key={m.id} className="whitespace-pre-wrap">
          {m.role === 'user' ? 'User: ' : 'AI: '}
          {m.content}
        </div>
      ))}

      <form onSubmit={handleSubmit}>
        <input
          className="fixed bottom-0 w-full max-w-md p-2 mb-8 border border-gray-300 rounded shadow-xl"
          value={input}
          placeholder="Say something..."
          onChange={handleInputChange}
        />
      </form>
    </div>
  );
}

Head back to your browser (http://localhost:3000) and enter a new message. You should see a JSON object appear with the value you sent from your API route!

Introducing more granular control with ai/rsc

So far, you have used Vercel AI SDK's UI package to connect your frontend to your API route. This package is framework agnostic and provides simple abstractions for quickly building chat-like interfaces with LLMs.

The Vercel AI SDK also has a package (ai/rsc) specifically designed for frameworks that support the React Server Component architecture. With ai/rsc, you can build AI applications that go beyond pure text.

Next.js App Router

The Next.js App Router is a React Server Component (RSC) framework. This means that pages and components are rendered on the server. Optionally, you can add directives, like "use client" when you want to add interactivity using Javascript and "use server" when you want to ensure code will only run on the server.

The server-first architecture of RSCs enables a number of powerful features, like Server Actions, which we will use as our server-side environment to query the language model.

Create a Server Action

Create your first Server Action (app/actions.tsx) and add the following code:

'use server';

import { createStreamableValue } from 'ai/rsc';
import { CoreMessage, streamText } from 'ai';
import { openai } from '@ai-sdk/openai';

export async function continueConversation(messages: CoreMessage[]) {
  const result = await streamText({
    model: openai('gpt-4-turbo'),
    messages,
  });

  const stream = createStreamableValue(result.textStream);
  return stream.value;
}

Let's take a look at what is happening in this code:

1. Add the "use server" directive at the top of the file to mark the function as a Server Action.
2. Define and export an async function (continueConversation) that takes one argument, messages, which is an array of type CoreMessage. The messages variable contains a history of the conversation between you and the chatbot and will provide the chatbot with the necessary context to make the next generation.
3. Call the streamText function which is imported from the ai package. To use this function, you pass it a configuration object that contains a model provider (imported from @ai-sdk/openai) and messages (defined in step 2). You can pass additional settings to further customise the model's behaviour.
4. Create a streamable value using the createStreamableValue function imported from the ai/rsc package. To use this function you pass the model's response as a text stream which can be accessed directly on the model response object (result.textStream).
5. Finally, return the value of the stream (stream.value).

Update the UI

Now that you have created a Server Action that can query an LLM, it's time to update your frontend. With ai/rsc, you have much finer control over how you send and receive streamable values from the LLM.

Update your root page (app/page.tsx) with the following code:

'use client';

import { type CoreMessage } from 'ai';
import { useState } from 'react';
import { continueConversation } from './actions';
import { readStreamableValue } from 'ai/rsc';

// Allow streaming responses up to 30 seconds
export const maxDuration = 30;

export default function Chat() {
  const [messages, setMessages] = useState<CoreMessage[]>([]);
  const [input, setInput] = useState('');
  return (
    <div className="flex flex-col w-full max-w-md py-24 mx-auto stretch">
      {messages.map((m, i) => (
        <div key={i} className="whitespace-pre-wrap">
          {m.role === 'user' ? 'User: ' : 'AI: '}
          {m.content as string}
        </div>
      ))}

      <form
        onSubmit={async e => {
          e.preventDefault();
          const newMessages: CoreMessage[] = [
            ...messages,
            { content: input, role: 'user' },
          ];

          setMessages(newMessages);
          setInput('');

          const result = await continueConversation(newMessages);

          for await (const content of readStreamableValue(result)) {
            setMessages([
              ...newMessages,
              {
                role: 'assistant',
                content: content as string,
              },
            ]);
          }
        }}
      >
        <input
          className="fixed bottom-0 w-full max-w-md p-2 mb-8 border border-gray-300 rounded shadow-xl"
          value={input}
          placeholder="Say something..."
          onChange={e => setInput(e.target.value)}
        />
      </form>
    </div>
  );
}

Let's look at how your implementation has changed. Without useChat, you have to manage your own state using the useState hook to manage the user's input and messages, respectively. The biggest change in your implementation is how you manage the form submission behaviour:

1. Define a new variable to house the existing messages and append the user's message.
2. Update the messages state by passing newMessages to the setMessages function.
3. Clear the input state with setInput("").
4. Call your Server Action just like any other asynchronous function, passing the newMessages variable declared in the first step. This function will return a streamable value.
5. Use an asynchronous for-loop in conjunction with the readStreamableValue function to iterate over the stream returned by the Server Action and read its value.
6. Finally, update the messages state with the content streamed via the Server Action.

Streaming Additional Data

Stream additional data alongside the response from the model by simply returning an additional value in your Server Action. Update your app/actions.tsxwith the following code:

'use server';

import { createStreamableValue } from 'ai/rsc';
import { CoreMessage, streamText } from 'ai';
import { openai } from '@ai-sdk/openai';

export async function continueConversation(messages: CoreMessage[]) {
  'use server';
  const result = await streamText({
    model: openai('gpt-4-turbo'),
    messages,
  });
  const data = { test: 'hello' };
  const stream = createStreamableValue(result.textStream);
  return { message: stream.value, data };
}

The only change that you make here is to declare a new value (data) and return it alongside the stream.

Update the UI

Update your root page with the following code:

'use client';

import { type CoreMessage } from 'ai';
import { useState } from 'react';
import { continueConversation } from './actions';
import { readStreamableValue } from 'ai/rsc';

// Allow streaming responses up to 30 seconds
export const maxDuration = 30;

export default function Chat() {
  const [messages, setMessages] = useState<CoreMessage[]>([]);
  const [input, setInput] = useState('');
  const [data, setData] = useState<any>();
  return (
    <div className="flex flex-col w-full max-w-md py-24 mx-auto stretch">
      {data && <pre>{JSON.stringify(data, null, 2)}</pre>}
      {messages.map((m, i) => (
        <div key={i} className="whitespace-pre-wrap">
          {m.role === 'user' ? 'User: ' : 'AI: '}
          {m.content as string}
        </div>
      ))}

      <form
        onSubmit={async e => {
          e.preventDefault();
          const newMessages: CoreMessage[] = [
            ...messages,
            { content: input, role: 'user' },
          ];

          setMessages(newMessages);
          setInput('');

          const result = await continueConversation(newMessages);
          setData(result.data);

          for await (const content of readStreamableValue(result.message)) {
            setMessages([
              ...newMessages,
              {
                role: 'assistant',
                content: content as string,
              },
            ]);
          }
        }}
      >
        <input
          className="fixed bottom-0 w-full max-w-md p-2 mb-8 border border-gray-300 rounded shadow-xl"
          value={input}
          placeholder="Say something..."
          onChange={e => setInput(e.target.value)}
        />
      </form>
    </div>
  );
}

In the code above, you first create a new variable to manage the state of the additional data (data). Then, you update the state of the additional data with setData(result.data). Just like that, you've sent additional data alongside the model's response.

The ai/rsc library is designed to give you complete control over streamable values. This unlocks LLM applications beyond the traditional chat format.

Where to Next?

You've built an AI chatbot using the Vercel AI SDK! Experiment and extend the functionality of this application further by exploring tool calling or introducing more granular control over AI and UI states.

If you are looking to leverage the broader capabilities of LLMs, Vercel AI SDK Core provides a comprehensive set of lower-level tools and APIs that will help you unlock a wider range of AI functionalities beyond the chatbot paradigm.