v0
storage
Vercel Blob Upload Failing with Size or Type Errors
File uploads to Vercel Blob Storage are failing in your v0-generated application. Users see generic error messages when trying to upload images, documents, or other files. The upload either times out, returns a 413 error, or fails silently with no file stored.
Vercel Blob has specific requirements around request body size, content types, and authentication tokens that v0 may not have configured correctly. The default Vercel serverless function body size limit of 4.5MB is often insufficient for image uploads.
Additionally, client-side upload implementations may fail due to CORS configuration issues or missing the BLOB_READ_WRITE_TOKEN environment variable in the correct scope.
Error Messages You Might See
BlobAccessError: Invalid token
Payload Too Large (413)
BlobUploadError: Failed to upload file
Failed to fetch blob upload URL
CORS error: Access-Control-Allow-Origin missing
Common Causes
- Body size limit exceeded — Vercel serverless functions have a 4.5MB body limit; large files need client-side upload
- Missing BLOB_READ_WRITE_TOKEN — environment variable not set or not available in the correct Vercel environment
- Wrong upload method — using server-side put() instead of client-side upload() for large files
- Content type not set — missing contentType option causes Blob to reject or misidentify the file
- CORS not configured — client-side uploads blocked by browser CORS policy
How to Fix It
- Use client-side uploads for large files — implement
upload()from @vercel/blob/client with a server-side token generation route - Set BLOB_READ_WRITE_TOKEN — add the token from Vercel Dashboard > Storage > Blob to your environment variables
- Configure upload route handler — create an API route that calls
handleUpload()from @vercel/blob for client uploads - Add content type detection — pass
contentType: file.typeor use automatic detection with the multipart upload option - Increase body size limit — export
const config = { api: { bodyParser: { sizeLimit: '10mb' } } }for server-side uploads
Real developers can help you.
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Get HelpFrequently Asked Questions
What is the maximum file size for Vercel Blob?
Server-side uploads are limited to 4.5MB by the serverless function body limit. Client-side uploads support up to 500MB using the @vercel/blob/client upload() method.
How do I get the BLOB_READ_WRITE_TOKEN?
Go to Vercel Dashboard > Storage > Create Blob Store. The token is automatically added to your project environment variables.
Can I upload to Vercel Blob from the browser directly?
Yes, use the upload() function from @vercel/blob/client. You need a server-side route handler that calls handleUpload() to generate secure upload URLs.