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ChatJS supports file attachments in conversations. Files are uploaded to Vercel Blob storage and processed by AI models that support multimodal input.
File attachments require BLOB_READ_WRITE_TOKEN. If you don’t need attachments, set integrations.attachments: false in chat.config.ts to run ChatJS without this env var.

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Supported File Types

TypeExtensionsProcessing
Images.png, .jpg, .jpegDirect vision input
PDFs.pdfText extraction

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How It Works

  1. User attaches file in chat input
  2. File uploads to Vercel Blob
  3. URL/content included in message
  4. Model processes based on type

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Configuration

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Enable/Disable

Toggle attachments in chat.config.ts: 
integrations: {
  attachments: true, // Requires BLOB_READ_WRITE_TOKEN
}
When disabled:
  • Attachment button is hidden from the chat input
  • Drag-and-drop and paste file handling are disabled
  • File upload API returns 503

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Environment Variables

Requires BLOB_READ_WRITE_TOKEN from Vercel Blob: 
BLOB_READ_WRITE_TOKEN=vercel_blob_...
On Vercel, this is auto-provided via the Blob integration.

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Attachment Settings

File attachment settings are configured in chat.config.ts under the attachments key: 
attachments: {
  maxBytes: 1024 * 1024,  // 1MB max after compression
  maxDimension: 2048,     // Max image width/height
  acceptedTypes: {
    "image/png": [".png"],
    "image/jpeg": [".jpg", ".jpeg"],
    "application/pdf": [".pdf"],
  },
},

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Mobile Behavior

On mobile devices, the attachment button shows a dropdown menu with separate options:
  • Add photos - Opens the device photo gallery
  • Take photo - Opens the camera directly
  • Add files - Opens the file browser for PDFs and documents
This granular selection is intentional: some mobile platforms default to the image picker when the file input accepts both images and other file types, making it difficult for users to select non-image files like PDFs.

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Model Support

Not all models support attachments. Check model.input for capability: 
if (model.input?.image) {
  // Model supports image inputs
}
if (model.input?.pdf) {
  // Model supports PDF inputs
}
When a user attaches a file that the current model doesn’t support, ChatJS automatically switches to a compatible model (configured via config.models.defaults.pdf and config.models.defaults.chatImageCompatible).