vercel-ai-sdk

# Vercel AI SDK

The Vercel AI SDK provides React hooks and server utilities for building streaming chat interfaces with support for tool calls, file attachments, and multi-step reasoning.

## Quick Reference

### Basic useChat Setup

```typescript
import { useChat } from '@ai-sdk/react';

const { messages, status, sendMessage, stop, regenerate } = useChat({
  id: 'chat-id',
  messages: initialMessages,
  onFinish: ({ message, messages, isAbort, isError }) => {
    console.log('Chat finished');
  },
  onError: (error) => {
    console.error('Chat error:', error);
  }
});

// Send a message
sendMessage({ text: 'Hello', metadata: { createdAt: Date.now() } });

// Send with files
sendMessage({
  text: 'Analyze this',
  files: fileList // FileList or FileUIPart[]
});
```

### ChatStatus States

The `status` field indicates the current state of the chat:

- **`ready`**: Chat is idle and ready to accept new messages
- **`submitted`**: Message sent to API, awaiting response stream start
- **`streaming`**: Response actively streaming from the API
- **`error`**: An error occurred during the request

### Message Structure

Messages use the `UIMessage` type with a parts-based structure:

```typescript
interface UIMessage {
  id: string;
  role: 'system' | 'user' | 'assistant';
  metadata?: unknown;
  parts: Array<UIMessagePart>; // text, file, tool-*, reasoning, etc.
}
```

Part types include:
- `text`: Text content with optional streaming state
- `file`: File attachments (images, documents)
- `tool-{toolName}`: Tool invocations with state machine
- `reasoning`: AI reasoning traces
- `data-{typeName}`: Custom data parts

### Server-Side Streaming

```typescript
import { streamText } from 'ai';
import { convertToModelMessages } from 'ai';

const result = streamText({
  model: openai('gpt-4'),
  messages: convertToModelMessages(uiMessages),
  tools: {
    getWeather: tool({
      description: 'Get weather',
      inputSchema: z.object({ city: z.string() }),
      execute: async