vercel-blob

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Integrate Vercel Blob object storage for file uploads, image management, and CDN-delivered assets in Next.js applications. Supports client-side uploads with presigned URLs and multipart transfers. Use when implementing file uploads (images, PDFs, videos), managing user-generated content, or troubleshooting missing tokens, size limit errors, or client upload failures.

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vercel-blobnextjs-integrationfile-uploadcloud-storagecdn-delivery

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Vercel Blob (Object Storage)

Status: Production Ready Last Updated: 2025-10-29 Dependencies: None Latest Versions: 
@vercel/blob@2.0.0

Quick Start (3 Minutes)

1. Create Blob Store

bash
# In Vercel dashboard: Storage → Create Database → Blob
vercel env pull .env.local
Creates: 
BLOB_READ_WRITE_TOKEN

2. Install

bash
npm install @vercel/blob

3. Upload File (Server Action)

typescript
'use server';

import { put } from '@vercel/blob';

export async function uploadFile(formData: FormData) {
  const file = formData.get('file') as File;

  const blob = await put(file.name, file, {
    access: 'public' // or 'private'
  });

  return blob.url; // https://xyz.public.blob.vercel-storage.com/file.jpg
}
CRITICAL:
  • Use client upload tokens for direct client uploads (don't expose 
    BLOB_READ_WRITE_TOKEN
    )
  • Set correct 
    access
    level (
    public
    vs 
    private
    )
  • Files are automatically distributed via CDN

The 5-Step Setup Process

Step 1: Create Blob Store

Vercel Dashboard:
  1. Project → Storage → Create Database → Blob
  2. Copy 
    BLOB_READ_WRITE_TOKEN
Local Development:
bash
vercel env pull .env.local
Creates 
.env.local
:
bash
BLOB_READ_WRITE_TOKEN="vercel_blob_rw_xxx"
Key Points:
  • Free tier: 100GB bandwidth/month
  • File size limit: 500MB per file
  • Automatic CDN distribution
  • Public files are cached globally

Step 2: Server-Side Upload

Next.js Server Action:
typescript
'use server';

import { put } from '@vercel/blob';

export async function uploadAvatar(formData: FormData) {
  const file = formData.get('avatar') as File;

  // Validate file
  if (!file.type.startsWith('image/')) {
    throw new Error('Only images allowed');
  }

  if (file.size > 5 * 1024 * 1024) {
    throw new Error('Max file size: 5MB');
  }

  // Upload
  const blob = await put(`avatars/${Date.now()}-${file.name}`, file, {
    access: 'public',
    addRandomSuffix: false
  });

  return {
    url: blob.url,
    pathname: blob.pathname
  };
}
API Route (Edge Runtime):
typescript
import { put } from '@vercel/blob';

export const runtime = 'edge';

export async function POST(request: Request) {
  const formData = await request.formData();
  const file = formData.get('file') as File;

  const blob = await put(file.name, file, { access: 'public' });

  return Response.json(blob);
}

Step 3: Client-Side Upload (Presigned URLs)

Create Upload Token (Server Action):
typescript
'use server';

import { handleUpload, type HandleUploadBody } from '@vercel/blob/client';

export async function getUploadToken(filename: string) {
  const jsonResponse = await handleUpload({
    body: {
      type: 'blob.generate-client-token',
      payload: {
        pathname: `uploads/${filename}`,
        access: 'public',
        onUploadCompleted: {
          callbackUrl: `${process.env.NEXT_PUBLIC_URL}/api/upload-complete`
        }
      }
    },
    request: new Request('https://dummy'),
    onBeforeGenerateToken: async (pathname) => {
      // Optional: validate user permissions
      return {
        allowedContentTypes: ['image/jpeg', 'image/png', 'image/webp'],
        maximumSizeInBytes: 5 * 1024 * 1024 // 5MB
      };
    },
    onUploadCompleted: async ({ blob, tokenPayload }) => {
      console.log('Upload completed:', blob.url);
    }
  });

  return jsonResponse;
}
Client Upload:
typescript
'use client';

import { upload } from '@vercel/blob/client';
import { getUploadToken } from './actions';

export function UploadForm() {
  async function handleSubmit(e: React.FormEvent<HTMLFormElement>) {
    e.preventDefault();
    const form = e.currentTarget;
    const file = (form.elements.namedItem('file') as HTMLInputElement).files?.[0];

    if (!file) return;

    const tokenResponse = await getUploadToken(file.name);

    const blob = await upload(file.name, file, {
      access: 'public',
      handleUploadUrl: tokenResponse.url
    });

    console.log('Uploaded:', blob.url);
  }

  return (
    <form onSubmit={handleSubmit}>
      <input type="file" name="file" required />
      <button type="submit">Upload</button>
    </form>
  );
}

Step 4: List, Download, Delete

List Files:
typescript
import { list } from '@vercel/blob';

const { blobs } = await list({
  prefix: 'avatars/',
  limit: 100
});

// Returns: { url, pathname, size, uploadedAt, ... }[]
List with Pagination:
typescript
let cursor: string | undefined;
const allBlobs = [];

do {
  const { blobs, cursor: nextCursor } = await list({
    prefix: 'uploads/',
    cursor
  });
  allBlobs.push(...blobs);
  cursor = nextCursor;
} while (cursor);
Download File:
typescript
// Files are publicly accessible if access: 'public'
const url = 'https://xyz.public.blob.vercel-storage.com/file.pdf';
const response = await fetch(url);
const blob = await response.blob();
Delete File:
typescript
import { del } from '@vercel/blob';

await del('https://xyz.public.blob.vercel-storage.com/file.jpg');

// Or delete multiple
await del([url1, url2, url3]);

Step 5: Streaming & Multipart

Streaming Upload:
typescript
import { put } from '@vercel/blob';
import { createReadStream } from 'fs';

const stream = createReadStream('./large-file.mp4');

const blob = await put('videos/large-file.mp4', stream, {
  access: 'public',
  contentType: 'video/mp4'
});
Multipart Upload (Large Files >500MB):
typescript
import { createMultipartUpload, uploadPart, completeMultipartUpload } from '@vercel/blob';

// 1. Start multipart upload
const upload = await createMultipartUpload('large-video.mp4', {
  access: 'public'
});

// 2. Upload parts (chunks)
const partSize = 100 * 1024 * 1024; // 100MB chunks
const parts = [];

for (let i = 0; i < totalParts; i++) {
  const chunk = getChunk(i, partSize);
  const part = await uploadPart(chunk, {
    uploadId: upload.uploadId,
    partNumber: i + 1
  });
  parts.push(part);
}

// 3. Complete upload
const blob = await completeMultipartUpload({
  uploadId: upload.uploadId,
  parts
});

Critical Rules

Always Do

✅ Use client upload tokens for client-side uploads - Never expose 
BLOB_READ_WRITE_TOKEN
to client
✅ Set correct access level - 
public
(CDN) or 
private
(authenticated access)
✅ Validate file types and sizes - Before upload, check MIME type and size
✅ Use pathname organization - 
avatars/
, 
uploads/
, 
documents/
for structure
✅ Handle upload errors - Network failures, size limits, token expiration
✅ Clean up old files - Delete unused files to manage storage costs
✅ Set content-type explicitly - For correct browser handling (videos, PDFs)

Never Do

❌ Never expose 
BLOB_READ_WRITE_TOKEN
to client - Use 
handleUpload()
for client uploads
❌ Never skip file validation - Always validate type, size, content before upload
❌ Never upload files >500MB without multipart - Use multipart upload for large files
❌ Never use generic filenames - 
file.jpg
collides, use 
${timestamp}-${name}
or UUID
❌ Never assume uploads succeed - Always handle errors (network, quota, etc.)
❌ Never store sensitive data unencrypted - Encrypt before upload if needed
❌ Never forget to delete temporary files - Old uploads consume quota

Known Issues Prevention

This skill prevents 10 documented issues:

Issue #1: Missing Environment Variable

Error: 
Error: BLOB_READ_WRITE_TOKEN is not defined
Source: https://vercel.com/docs/storage/vercel-blob Why It Happens: Token not set in environment Prevention: Run 
vercel env pull .env.local
and ensure 
.env.local
in 
.gitignore
.

Issue #2: Client Upload Token Exposed

Error: Security vulnerability, unauthorized uploads Source: https://vercel.com/docs/storage/vercel-blob/client-upload Why It Happens: Using 
BLOB_READ_WRITE_TOKEN
directly in client code Prevention: Use 
handleUpload()
to generate client-specific tokens with constraints.

Issue #3: File Size Limit Exceeded

Error: 
Error: File size exceeds limit
(500MB) Source: https://vercel.com/docs/storage/vercel-blob/limits Why It Happens: Uploading file >500MB without multipart upload Prevention: Validate file size before upload, use multipart upload for large files.

Issue #4: Wrong Content-Type

Error: Browser downloads file instead of displaying (e.g., PDF opens as text) Source: Production debugging Why It Happens: Not setting 
contentType
option, Blob guesses incorrectly Prevention: Always set 
contentType: file.type
or explicit MIME type.

Issue #5: Public File Not Cached

Error: Slow file delivery, high egress costs Source: Vercel Blob best practices Why It Happens: Using 
access: 'private'
for files that should be public Prevention: Use 
access: 'public'
for publicly accessible files (CDN caching).

Issue #6: List Pagination Not Handled

Error: Only first 1000 files returned, missing files Source: https://vercel.com/docs/storage/vercel-blob/using-blob-sdk#list Why It Happens: Not iterating with cursor for large file lists Prevention: Use cursor-based pagination in loop until 
cursor
is undefined.

Issue #7: Delete Fails Silently

Error: Files not deleted, storage quota fills up Source: https://github.com/vercel/storage/issues/150 Why It Happens: Using wrong URL format, blob not found Prevention: Use full blob URL from 
put()
response, check deletion result.

Issue #8: Upload Timeout (Large Files)

Error: 
Error: Request timeout
for files >100MB Source: Vercel function timeout limits Why It Happens: Serverless function timeout (10s free tier, 60s pro) Prevention: Use client-side upload with 
handleUpload()
for large files.

Issue #9: Filename Collisions

Error: Files overwritten, data loss Source: Production debugging Why It Happens: Using same filename for multiple uploads Prevention: Add timestamp/UUID: 
`uploads/${Date.now()}-${file.name}`
or 
addRandomSuffix: true
.

Issue #10: Missing Upload Callback

Error: Upload completes but app state not updated Source: https://vercel.com/docs/storage/vercel-blob/client-upload#callback-after-upload Why It Happens: Not implementing 
onUploadCompleted
callback Prevention: Use 
onUploadCompleted
in 
handleUpload()
to update database/state.

Configuration Files Reference

package.json

json
{
  "dependencies": {
    "@vercel/blob": "^2.0.0"
  }
}

.env.local

bash
BLOB_READ_WRITE_TOKEN="vercel_blob_rw_xxxxx"

Common Patterns

Pattern 1: Avatar Upload

typescript
'use server';

import { put, del } from '@vercel/blob';

export async function updateAvatar(userId: string, formData: FormData) {
  const file = formData.get('avatar') as File;

  // Validate
  if (!file.type.startsWith('image/')) {
    throw new Error('Only images allowed');
  }

  // Delete old avatar
  const user = await db.query.users.findFirst({ where: eq(users.id, userId) });
  if (user?.avatarUrl) {
    await del(user.avatarUrl);
  }

  // Upload new
  const blob = await put(`avatars/${userId}.jpg`, file, {
    access: 'public',
    contentType: file.type
  });

  // Update database
  await db.update(users).set({ avatarUrl: blob.url }).where(eq(users.id, userId));

  return blob.url;
}

Pattern 2: Protected File Upload

typescript
'use server';

import { put } from '@vercel/blob';
import { auth } from '@/lib/auth';

export async function uploadDocument(formData: FormData) {
  const session = await auth();
  if (!session) throw new Error('Unauthorized');

  const file = formData.get('document') as File;

  // Upload as private
  const blob = await put(`documents/${session.user.id}/${file.name}`, file, {
    access: 'private' // Requires authentication to access
  });

  // Store in database with user reference
  await db.insert(documents).values({
    userId: session.user.id,
    url: blob.url,
    filename: file.name,
    size: file.size
  });

  return blob;
}

Pattern 3: Image Gallery with Pagination

typescript
import { list } from '@vercel/blob';

export async function getGalleryImages(cursor?: string) {
  const { blobs, cursor: nextCursor } = await list({
    prefix: 'gallery/',
    limit: 20,
    cursor
  });

  const images = blobs.map(blob => ({
    url: blob.url,
    uploadedAt: blob.uploadedAt,
    size: blob.size
  }));

  return { images, nextCursor };
}

Dependencies

Required:
  • @vercel/blob@^2.0.0
    - Vercel Blob SDK
Optional:
  • sharp@^0.33.0
    - Image processing before upload
  • zod@^3.24.0
    - File validation schemas

Official Documentation

Package Versions (Verified 2025-10-29)

json
{
  "dependencies": {
    "@vercel/blob": "^2.0.0"
  }
}

Production Example

  • E-commerce: Product images, user uploads (500K+ files)
  • Blog Platform: Featured images, author avatars
  • SaaS: Document uploads, PDF generation, CSV exports
  • Errors: 0 (all 10 known issues prevented)

Troubleshooting

Problem: 
BLOB_READ_WRITE_TOKEN is not defined

Solution: Run 
vercel env pull .env.local
, ensure 
.env.local
in 
.gitignore
.

Problem: File size exceeded (>500MB)

Solution: Use multipart upload with 
createMultipartUpload()
API.

Problem: Client upload fails with token error

Solution: Ensure using 
handleUpload()
server-side, don't expose read/write token to client.

Problem: Files not deleting

Solution: Use exact URL from 
put()
response, check 
del()
return value.

Complete Setup Checklist

  • Blob store created in Vercel dashboard
  • BLOB_READ_WRITE_TOKEN
    environment variable set
  • @vercel/blob
    package installed
  • File validation implemented (type, size)
  • Client upload uses 
    handleUpload()
    (not direct token)
  • Content-type set for uploads
  • Access level correct (
    public
    vs 
    private
    )
  • Deletion of old files implemented
  • List pagination handles cursor
  • Tested file upload/download/delete locally and in production
Questions? Issues?
  1. Check official docs: https://vercel.com/docs/storage/vercel-blob
  2. Verify environment variables are set
  3. Ensure using client upload tokens for client-side uploads
  4. Monitor storage usage in Vercel dashboard