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GuidesIntegrationsAPI ReferencesRelease notes
  • Introduction
    • Overview
    • Quick Start
    • Projects
    • Billing
  • Uploading
    • Overview
    • Uploading files with API
    • File analysis on upload
  • Optimization
    • Overview
  • Transformations
  • Delivery
    • Overview
    • On-the-fly operations
    • CDN settings
    • Proxy
  • Security
    • Overview
    • Validation and moderation
    • Signed uploads
    • Signed URLs
    • Unsafe content moderation
    • Malware protection
    • HIPAA workflows
  • Storage
    • Uploadcare storage
    • Cloudflare R2
    • Google Cloud Storage
    • Azure Blob Storage
  • File management
    • Overview
    • Managing files
    • File groups
    • Webhooks
    • Arbitrary file metadata
  • CLI
    • Overview
    • Configuration
  • Migration
    • Migration to Uploadcare
    • Migration from Filestack
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On this page
  • How it works
  • Search engine optimization
  • Table of Contents
Delivery

File delivery with Uploadcare

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List of on-the-fly CDN operations

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Built with

Every uploaded file is immediately available on the Uploadcare CDN — the best place to host your files for media delivery.

CDN domains — effective since September 4, 2025

By default, files are delivered from your personal subdomain on :subdomain.ucarecd.net. The legacy global domain ucarecdn.com is available for accounts created before September 4, 2025.

  • Global CDN network
  • Fastest on-the-fly image operations
  • Huge set of image transformations
  • Deliver files from any remote storage
  • Access control
  • Unlimited scalability on demand

CDN is a geographically distributed system of servers that delivers content to client devices from the servers nearby, which saves time on long-distance data exchange.

While traditional CDNs are typically limited to basic copying and caching functions, Uploadcare CDN stands out by offering dynamic image modifications. This unique feature not only ensures faster page load times and better uptime, but also allows on-the-fly image optimization and transformation to suit the device they are being consumed on.

How it works

Access files in Uploadcare CDN using subdomains by default:

1https://:subdomain.ucarecd.net/:uuid/
2https://:subdomain.ucarecd.net/:uuid/-/:operation/:params/:filename
https://:subdomain.ucarecd.net/:uuid/

You can add CDN operations by including directives in the CDN URL:

https://:subdomain.ucarecd.net/:uuid/-/:operation/:params/:filename
  • :subdomain is your project’s subdomain — find it in Delivery.
  • :uuid stands for the unique file identifier, UUID, assigned on upload.
  • /-/ is a mandatory parsing delimiter to divide operations and other path components.
  • :operation/:params/ is a CDN operation directive with parameters.
  • :filename is an optional filename you can add after a trailing slash /.

You can stack two and more operations like this:

/:operation/:params/-/:operation/:params/

Same applies when using Proxy:

https://yoursite.ucr.io/-/preview/-/resize/500x/https://yoursite.com/assets/image.jpg

Search engine optimization

One way to improve your site’s SEO is to name your files relevantly, such as integrating keywords into your image URLs.

Valid URLs typically have words separated by a hyphen, for example seo-optimize-images.

You can specify an additional filename after the UUID instead of the automatically generated one:

https://:subdomain.ucarecd.net/:uuid/:filename

The filename can be added to both the original (after the UUID) and at the end of the URL with operations applied, as in the example above.

Table of Contents

ArticleDescription
On-the-fly operationsUploadcare CDN features on-the-fly image optimization, large set of image transformations, and non-image file operations, such as getting file information or changing file delivery behavior
Image optimizationScale your images and compress them without sacrificing quality to improve the performance of your website or application
Image transformationsBuild custom image processing workflows and automate most image transformation tasks: scaling, rotation, overlays, effects and enhancements, face-detection, SVG transformation and many more
CDN settingsSet up custom CDN CNAME, cache duration, search engine indexing behavior, or even bring your own CDN
Fetch and deliver remote filesWhen you need to get all the benefits of image optimization for files that you already store somewhere else, use Proxy. It automatically retrieves files from existing remote locations and delivers them using the CDN
Signed URLsControl who and for how long can access files in your project via signed URLs. Protect end-users sensitive data, authorize clients, limit access by time
URL APIList of all CDN operations, its limitations, and settings