name	cloudflare-images
description	Store and transform images with Cloudflare Images API and transformations. Use when: uploading images, implementing direct creator uploads, creating variants, generating signed URLs, optimizing formats (WebP/AVIF), transforming via Workers, or debugging CORS, multipart, or error codes 9401-9413.

Cloudflare Images

Status: Production Ready ✅ Last Updated: 2025-11-23 Dependencies: Cloudflare account with Images enabled Latest Versions: Cloudflare Images API v2, @cloudflare/workers-types@4.20251121.0

Recent Updates (2025):

August 2025: AI Face Cropping GA (gravity=face with zoom control, GPU-based RetinaFace, 99.4% precision)
May 2025: Media Transformations origin restrictions (default: same-domain only, configurable via dashboard)
Upcoming: Background removal, generative upscale (planned features)

Overview

Two features: Images API (upload/store with variants) and Image Transformations (resize any image via URL or Workers).

Quick Start

1. Enable: Dashboard → Images → Get Account ID + API token (Cloudflare Images: Edit permission)

2. Upload:

curl -X POST https://api.cloudflare.com/client/v4/accounts/<ACCOUNT_ID>/images/v1 \
  -H 'Authorization: Bearer <API_TOKEN>' \
  -H 'Content-Type: multipart/form-data' \
  -F 'file=@./image.jpg'

3. Serve: https://imagedelivery.net/<ACCOUNT_HASH>/<IMAGE_ID>/public

4. Transform (optional): Dashboard → Images → Transformations → Enable for zone

<img src="/cdn-cgi/image/width=800,quality=85/uploads/photo.jpg" />

Upload Methods

1. File Upload: POST to /images/v1 with file (multipart/form-data), optional id, requireSignedURLs, metadata

2. Upload via URL: POST with url=https://example.com/image.jpg (supports HTTP basic auth)

3. Direct Creator Upload (one-time URLs, no API key exposure):

Backend: POST to /images/v2/direct_upload → returns uploadURL Frontend: POST file to uploadURL with FormData

CRITICAL CORS FIX:

✅ Use multipart/form-data (let browser set header)
✅ Name field file (NOT image)
✅ Call /direct_upload from backend only
❌ Don't set Content-Type: application/json
❌ Don't call /direct_upload from browser

Image Transformations

URL: /cdn-cgi/image/<OPTIONS>/<SOURCE>

Sizing: width=800,height=600,fit=cover
Quality: quality=85 (1-100)
Format: format=auto (WebP/AVIF auto-detection)
Cropping: gravity=auto (smart crop), gravity=face (AI face detection, Aug 2025 GA), gravity=center, zoom=0.5 (0-1 range, face crop tightness)
Effects: blur=10,sharpen=3,brightness=1.2
Fit: scale-down, contain, cover, crop, pad

Workers: Use cf.image object in fetch

fetch(imageURL, {
  cf: {
    image: { width: 800, quality: 85, format: 'auto', gravity: 'face', zoom: 0.8 }
  }
});

Variants

Named Variants (up to 100): Predefined transformations (e.g., avatar, thumbnail)

Create: POST to /images/v1/variants with id, options
Use: imagedelivery.net/<HASH>/<ID>/avatar
Works with signed URLs

Flexible Variants: Dynamic params in URL (w=400,sharpen=3)

Enable: PATCH /images/v1/config with {"flexible_variants": true}
❌ Cannot use with signed URLs (use named variants instead)

Signed URLs

Generate HMAC-SHA256 tokens for private images (URL format: ?exp=<TIMESTAMP>&sig=<HMAC>).

Algorithm: HMAC-SHA256(signingKey, imageId + variant + expiry) → hex signature

See: templates/signed-urls-generation.ts for Workers implementation

Critical Rules

Always Do

✅ Use multipart/form-data for Direct Creator Upload ✅ Name the file field file (not image or other names) ✅ Call /direct_upload API from backend only (NOT browser) ✅ Use HTTPS URLs for transformations (HTTP not supported) ✅ URL-encode special characters in image paths ✅ Enable transformations on zone before using /cdn-cgi/image/ ✅ Use named variants for private images (signed URLs) ✅ Check Cf-Resized header for transformation errors ✅ Set format=auto for automatic WebP/AVIF conversion ✅ Use fit=scale-down to prevent unwanted enlargement

Never Do

❌ Use application/json Content-Type for file uploads ❌ Call /direct_upload from browser (CORS will fail) ❌ Use flexible variants with requireSignedURLs=true ❌ Resize SVG files (they're inherently scalable) ❌ Use HTTP URLs for transformations (HTTPS only) ❌ Put spaces or unescaped Unicode in URLs ❌ Transform the same image multiple times in Workers (causes 9403 loop) ❌ Exceed 100 megapixels image size ❌ Use /cdn-cgi/image/ endpoint in Workers (use cf.image instead) ❌ Forget to enable transformations on zone before use

Known Issues Prevention

This skill prevents 13+ documented issues.

Issue #1: Direct Creator Upload CORS Error

Error: Access to XMLHttpRequest blocked by CORS policy: Request header field content-type is not allowed

Source: Cloudflare Community #345739, #368114

Why It Happens: Server CORS settings only allow multipart/form-data for Content-Type header

Prevention:

// ✅ CORRECT
const formData = new FormData();
formData.append('file', fileInput.files[0]);
await fetch(uploadURL, {
  method: 'POST',
  body: formData // Browser sets multipart/form-data automatically
});

// ❌ WRONG
await fetch(uploadURL, {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' }, // CORS error
  body: JSON.stringify({ file: base64Image })
});

Issue #2: Error 5408 - Upload Timeout

Error: Error 5408 after ~15 seconds of upload

Source: Cloudflare Community #571336

Why It Happens: Cloudflare has 30-second request timeout; slow uploads or large files exceed limit

Prevention:

Compress images before upload (client-side with Canvas API)
Use reasonable file size limits (e.g., max 10MB)
Show upload progress to user
Handle timeout errors gracefully

const MAX_FILE_SIZE = 10 * 1024 * 1024; // 10MB

if (file.size > MAX_FILE_SIZE) {
  alert('File too large. Please select an image under 10MB.');
  return;
}

Issue #3: Error 400 - Invalid File Parameter

Error: 400 Bad Request with unhelpful error message

Source: Cloudflare Community #487629

Why It Happens: File field must be named file (not image, photo, etc.)

Prevention:

// ✅ CORRECT
formData.append('file', imageFile);

// ❌ WRONG
formData.append('image', imageFile); // 400 error
formData.append('photo', imageFile); // 400 error

Issue #4: CORS Preflight Failures

Error: Preflight OPTIONS request blocked

Source: Cloudflare Community #306805

Why It Happens: Calling /direct_upload API directly from browser (should be backend-only)

Prevention:

ARCHITECTURE:
Browser → Backend API → POST /direct_upload → Returns uploadURL → Browser uploads to uploadURL

Never expose API token to browser. Generate upload URL on backend, return to frontend.

Issue #5: Error 9401 - Invalid Arguments

Error: Cf-Resized: err=9401 - Required cf.image options missing or invalid

Source: Cloudflare Images Docs - Troubleshooting

Why It Happens: Missing required transformation parameters or invalid values

Prevention:

// ✅ CORRECT
fetch(imageURL, {
  cf: {
    image: {
      width: 800,
      quality: 85,
      format: 'auto'
    }
  }
});

// ❌ WRONG
fetch(imageURL, {
  cf: {
    image: {
      width: 'large', // Must be number
      quality: 150 // Max 100
    }
  }
});

Issue #6: Error 9402 - Image Too Large

Error: Cf-Resized: err=9402 - Image too large or connection interrupted

Source: Cloudflare Images Docs - Troubleshooting

Why It Happens: Image exceeds maximum area (100 megapixels) or download fails

Prevention:

Validate image dimensions before transforming
Use reasonable source images (max 10000x10000px)
Handle network errors gracefully

Issue #7: Error 9403 - Request Loop

Error: Cf-Resized: err=9403 - Worker fetching its own URL or already-resized image

Source: Cloudflare Images Docs - Troubleshooting

Why It Happens: Transformation applied to already-transformed image, or Worker fetches itself

Prevention:

// ✅ CORRECT
if (url.pathname.startsWith('/images/')) {
  const originalPath = url.pathname.replace('/images/', '');
  const originURL = `https://storage.example.com/${originalPath}`;
  return fetch(originURL, { cf: { image: { width: 800 } } });
}

// ❌ WRONG
if (url.pathname.startsWith('/images/')) {
  // Fetches worker's own URL, causes loop
  return fetch(request, { cf: { image: { width: 800 } } });
}

Issue #8: Error 9406/9419 - Invalid URL Format

Error: Cf-Resized: err=9406 or err=9419 - Non-HTTPS URL or URL has spaces/unescaped Unicode

Source: Cloudflare Images Docs - Troubleshooting

Why It Happens: Image URL uses HTTP (not HTTPS) or contains invalid characters

Prevention:

// ✅ CORRECT
const imageURL = "https://example.com/images/photo%20name.jpg";

// ❌ WRONG
const imageURL = "http://example.com/images/photo.jpg"; // HTTP not allowed
const imageURL = "https://example.com/images/photo name.jpg"; // Space not encoded

Always use encodeURIComponent() for URL paths:

const filename = "photo name.jpg";
const imageURL = `https://example.com/images/${encodeURIComponent(filename)}`;

Issue #9: Error 9412 - Non-Image Response

Error: Cf-Resized: err=9412 - Origin returned HTML instead of image

Source: Cloudflare Images Docs - Troubleshooting

Why It Happens: Origin server returns 404 page or error page (HTML) instead of image

Prevention:

// Verify URL before transforming
const originResponse = await fetch(imageURL, { method: 'HEAD' });
const contentType = originResponse.headers.get('content-type');

if (!contentType?.startsWith('image/')) {
  return new Response('Not an image', { status: 400 });
}

return fetch(imageURL, { cf: { image: { width: 800 } } });

Issue #10: Error 9413 - Max Image Area Exceeded

Error: Cf-Resized: err=9413 - Image exceeds 100 megapixels

Source: Cloudflare Images Docs - Troubleshooting

Why It Happens: Source image dimensions exceed 100 megapixels (e.g., 10000x10000px)

Prevention:

Validate image dimensions before upload
Pre-process oversized images
Reject images above threshold

const MAX_MEGAPIXELS = 100;

if (width * height > MAX_MEGAPIXELS * 1_000_000) {
  return new Response('Image too large', { status: 413 });
}

Issue #11: Flexible Variants + Signed URLs Incompatibility

Error: Flexible variants don't work with private images

Source: Cloudflare Images Docs - Enable flexible variants

Why It Happens: Flexible variants cannot be used with requireSignedURLs=true

Prevention:

// ✅ CORRECT - Use named variants for private images
await uploadImage({
  file: imageFile,
  requireSignedURLs: true // Use named variants: /public, /avatar, etc.
});

// ❌ WRONG - Flexible variants don't support signed URLs
// Cannot use: /w=400,sharpen=3 with requireSignedURLs=true

Issue #12: SVG Resizing Limitation

Error: SVG files don't resize via transformations

Source: Cloudflare Images Docs - SVG files

Why It Happens: SVG is inherently scalable (vector format), resizing not applicable

Prevention:

// SVGs can be served but not resized
// Use any variant name as placeholder
// https://imagedelivery.net/<HASH>/<SVG_ID>/public

// SVG will be served at original size regardless of variant settings

Issue #13: EXIF Metadata Stripped by Default

Error: GPS data, camera settings removed from uploaded JPEGs

Source: Cloudflare Images Docs - Transform via URL

Why It Happens: Default behavior strips all metadata except copyright

Prevention:

// Preserve metadata
fetch(imageURL, {
  cf: {
    image: {
      width: 800,
      metadata: 'keep' // Options: 'none', 'copyright', 'keep'
    }
  }
});

Options:

none: Strip all metadata
copyright: Keep only copyright tag (default for JPEG)
keep: Preserve most EXIF metadata including GPS

Using Bundled Resources

Templates (templates/)

Copy-paste ready code for common patterns:

wrangler-images-binding.jsonc - Wrangler configuration (no binding needed)
upload-api-basic.ts - Upload file to Images API
upload-via-url.ts - Ingest image from external URL
direct-creator-upload-backend.ts - Generate one-time upload URLs
direct-creator-upload-frontend.html - User upload form
transform-via-url.ts - URL transformation examples
transform-via-workers.ts - Workers transformation patterns
variants-management.ts - Create/list/delete variants
signed-urls-generation.ts - HMAC-SHA256 signed URL generation
responsive-images-srcset.html - Responsive image patterns
batch-upload.ts - Batch API for high-volume uploads

Usage:

cp templates/upload-api-basic.ts src/upload.ts
# Edit with your account ID and API token

References (references/)

In-depth documentation Claude can load as needed:

api-reference.md - Complete API endpoints (upload, list, delete, variants)
transformation-options.md - All transform params with examples
variants-guide.md - Named vs flexible variants, when to use each
signed-urls-guide.md - HMAC-SHA256 implementation details
direct-upload-complete-workflow.md - Full architecture and flow
responsive-images-patterns.md - srcset, sizes, art direction
format-optimization.md - WebP/AVIF auto-conversion strategies
top-errors.md - All 13+ errors with detailed troubleshooting

When to load:

Deep-dive into specific feature
Troubleshooting complex issues
Understanding API details
Implementing advanced patterns

Scripts (scripts/)

check-versions.sh - Verify API endpoints are current

Advanced Topics

Custom Domains: Serve from your domain via /cdn-cgi/imagedelivery/<HASH>/<ID>/<VARIANT> (requires domain on Cloudflare, proxied). Use Transform Rules for custom paths.

Batch API: High-volume uploads via batch.imagedelivery.net with batch tokens (Dashboard → Images → Batch API)

Webhooks: Notifications for Direct Creator Upload (Dashboard → Notifications → Webhooks). Payload includes imageId, status, metadata.

Troubleshooting

Problem: Images not transforming

Symptoms: /cdn-cgi/image/... returns original image or 404

Solutions:

Enable transformations on zone: Dashboard → Images → Transformations → Enable for zone
Verify zone is proxied through Cloudflare (orange cloud)
Check source image is publicly accessible
Wait 5-10 minutes for settings to propagate

Problem: Direct upload returns CORS error

Symptoms: Access-Control-Allow-Origin error in browser console

Solutions:

Use multipart/form-data encoding (let browser set Content-Type)
Don't call /direct_upload from browser; call from backend
Name file field file (not image)
Remove manual Content-Type header

Problem: Worker transformations return 9403 loop error

Symptoms: Cf-Resized: err=9403 in response headers

Solutions:

Don't fetch Worker's own URL (use external origin)
Don't transform already-resized images
Check URL routing logic to avoid loops

Problem: Signed URLs not working

Symptoms: 403 Forbidden when accessing signed URL

Solutions:

Verify image uploaded with requireSignedURLs=true
Check signature generation (HMAC-SHA256)
Ensure expiry timestamp is in future
Verify signing key matches dashboard (Images → Keys)
Cannot use flexible variants with signed URLs (use named variants)

Problem: Images uploaded but not appearing

Symptoms: Upload returns 200 OK but image not in dashboard

Solutions:

Check for draft: true in response (Direct Creator Upload)
Wait for upload to complete (check via GET /images/v1/{id})
Verify account ID matches
Check for upload errors in webhooks

Official Documentation

Cloudflare Images: https://developers.cloudflare.com/images/
Get Started: https://developers.cloudflare.com/images/get-started/
Upload Images: https://developers.cloudflare.com/images/upload-images/
Direct Creator Upload: https://developers.cloudflare.com/images/upload-images/direct-creator-upload/
Transform Images: https://developers.cloudflare.com/images/transform-images/
Transform via URL: https://developers.cloudflare.com/images/transform-images/transform-via-url/
Transform via Workers: https://developers.cloudflare.com/images/transform-images/transform-via-workers/
Create Variants: https://developers.cloudflare.com/images/manage-images/create-variants/
Serve Private Images: https://developers.cloudflare.com/images/manage-images/serve-images/serve-private-images/
Troubleshooting: https://developers.cloudflare.com/images/reference/troubleshooting/
API Reference: https://developers.cloudflare.com/api/resources/images/

Package Versions

Last Verified: 2025-11-23 API Version: v2 (direct uploads), v1 (standard uploads) Optional: @cloudflare/workers-types@4.20251121.0

cloudflare-images

Install Skill

SKILL.md

Cloudflare Images

Overview

Quick Start

Upload Methods

Image Transformations

Variants

Signed URLs

Critical Rules

Always Do

Never Do

Known Issues Prevention

Issue #1: Direct Creator Upload CORS Error

Issue #2: Error 5408 - Upload Timeout

Issue #3: Error 400 - Invalid File Parameter

Issue #4: CORS Preflight Failures

Issue #5: Error 9401 - Invalid Arguments

Issue #6: Error 9402 - Image Too Large

Issue #7: Error 9403 - Request Loop

Issue #8: Error 9406/9419 - Invalid URL Format

Issue #9: Error 9412 - Non-Image Response

Issue #10: Error 9413 - Max Image Area Exceeded

Issue #11: Flexible Variants + Signed URLs Incompatibility

Issue #12: SVG Resizing Limitation

Issue #13: EXIF Metadata Stripped by Default

Using Bundled Resources

Templates (templates/)

References (references/)

Scripts (scripts/)

Advanced Topics

Troubleshooting

Problem: Images not transforming

Problem: Direct upload returns CORS error

Problem: Worker transformations return 9403 loop error

Problem: Signed URLs not working

Problem: Images uploaded but not appearing

Official Documentation

Package Versions