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
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.
Matthew Jordan
I've been working at a large software company named Kainos for 2 years, and mainly specialise in Platform Engineering. I regularly enjoy working on software products outside of work, and I'm a huge fan of game development using Unity. I personally enjoy Python & C# in my spare time, but I also specialise in multiple different platform-related technologies from my day job.
Krishna Sai Kuncha
Experienced Professional Full stack Developer with 8+ years of experience across react, python, js, ts, golang and react-native. Developed inhouse websearch tooling for AI before websearch was solved : )
Pratik
SWE with 15+ years of experience building and maintaining web apps and extensive BE infrastructure
Simon A.
I'm a backend developer building APIs, emulators, and interactive game systems. Professionally, I've developed Java/Spring reporting solutions, managed relational and NoSQL databases, and implemented CI/CD workflows.
Tejas Chokhawala
Full-stack engineer with 5 years experience building production web apps using React, Next.js and TypeScript.
Focused on performance, clean architecture and shipping fast.
Experienced with Supabase/Postgres backends, Stripe billing, and building AI-assisted developer tools.
Mehdi Ben Haddou
- Founder of Chessigma (1M+ users) & many small projects
- ex Founding Engineer @Uplane (YC F25)
- ex Software Engineer @Amazon and @Booking.com
prajwalfullstack
Hi Im a full stack developer, a vibe coded MVP to Market ready product, I'm here to help
Dor Yaloz
SW engineer with 6+ years of experience,
I worked with React/Node/Python
did projects with React+Capacitor.js for ios
Supabase expert
Nam Tran
10 years as fullstack developer
Milan Surelia
Milan Surelia is a Mobile App Developer with 5+ years of experience crafting scalable, cross-platform apps at 7Span and Meticha. At 7Span, he engineers feature-rich Flutter apps with smooth performance and modern UI. As the Co-Founder of Meticha, he builds open-source tools and developer-focused products that solve real-world problems.
Expertise:
💡 Developing cross-platform apps using Flutter, Dart, and Jetpack Compose for Android, iOS, and Web.
🖋️ Sharing insights through technical writing, blogging, and open-source contributions.
🤝 Collaborating closely with designers, PMs, and developers to build seamless mobile experiences.
Notable Achievements:
🎯 Revamped the Vepaar app into Vepaar Store & CRM with a 2x performance boost and smoother UX.
🚀 Launched Compose101 — a Jetpack Compose starter kit to speed up Android development.
🌟 Open source contributions on Github & StackOverflow for Flutter & Dart
🎖️ Worked on improving app performance and user experience with smart solutions.
Milan is always happy to connect, work on new ideas, and explore the latest in technology.
You don't need to be technical. Just describe what's wrong and a verified developer will handle the rest.
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.