Express

You can use the AI SDK in an Express server to generate and stream text and objects to the client.

Examples

The examples start a simple HTTP server that listens on port 8080. You can e.g. test it using curl:

curl -X POST http://localhost:8080

The examples use the OpenAI gpt-4o model. Ensure that the OpenAI API key is set in the OPENAI_API_KEY environment variable.

Full example: github.com/vercel/ai/examples/express

Data Stream

You can use the pipeDataStreamToResponse method to pipe the stream data to the server response.

index.ts

import { openai } from '@ai-sdk/openai';
import { streamText } from 'ai';
import express, { Request, Response } from 'express';

const app = express();

app.post('/', async (req: Request, res: Response) => {
  const result = streamText({
    model: openai('gpt-4o'),
    prompt: 'Invent a new holiday and describe its traditions.',
  });

  result.pipeDataStreamToResponse(res);
});

app.listen(8080, () => {
  console.log(`Example app listening on port ${8080}`);
});

Sending Custom Data

pipeDataStreamToResponse can be used to send custom data to the client.

index.ts

import { openai } from '@ai-sdk/openai';
import { pipeDataStreamToResponse, streamText } from 'ai';
import express, { Request, Response } from 'express';

const app = express();

app.post('/stream-data', async (req: Request, res: Response) => {
  // immediately start streaming the response
  pipeDataStreamToResponse(res, {
    execute: async dataStreamWriter => {
      dataStreamWriter.writeData('initialized call');

      const result = streamText({
        model: openai('gpt-4o'),
        prompt: 'Invent a new holiday and describe its traditions.',
      });

      result.mergeIntoDataStream(dataStreamWriter);
    },
    onError: error => {
      // Error messages are masked by default for security reasons.
      // If you want to expose the error message to the client, you can do so here:
      return error instanceof Error ? error.message : String(error);
    },
  });
});

app.listen(8080, () => {
  console.log(`Example app listening on port ${8080}`);
});

Text Stream

You can send a text stream to the client using pipeTextStreamToResponse.

index.ts

import { openai } from '@ai-sdk/openai';
import { streamText } from 'ai';
import express, { Request, Response } from 'express';

const app = express();

app.post('/', async (req: Request, res: Response) => {
  const result = streamText({
    model: openai('gpt-4o'),
    prompt: 'Invent a new holiday and describe its traditions.',
  });

  result.pipeTextStreamToResponse(res);
});

app.listen(8080, () => {
  console.log(`Example app listening on port ${8080}`);
});