Content Delivery Network

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. In addition to faster page load, delivery networks store cached files on multiple servers and provide a better uptime in case some servers become inaccessable.

Uploadcare uses Akamai CDN and a proprietary CDN layer for better performance and reliability.

CDN operations

Access files in Uploadcare CDN at over HTTP/HTTPS liks this:

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



Your original filenames can be accessed via REST API. Make a request to receive a JSON response with file parameters including original_filename.

You can set an optional filename that users will see instead of the original name:

:filename should comply with file name conventions and it should be a valid part of a URL. For example, filename.ext.

Here are some examples with full CDN URLs:

Group API

What a group is

Groups are file collections. Use them to organize content in your Uploadcare project. A common use case is to use them in single content upload or delivery transactions.

For instance, each time you use multi-upload with File Uploader, a new group is created. It stores UUIDs of uploaded files. You can access file collections via :group_uuid:

:group_uuid is similar to a single file UUID, but it has the file number ~N at the end. A group can contain up to 1000 files.

A group URL will show a list of individual file URLs with their UUIDs, and index numbers in that group.

Technically, our File Uploader will create a group on multi-upload using Uploadcare APIs. Learn more about creating and managing groups.

Accessing single files in a group

Request a specific file in a group by adding /nth/i/, where i is a file index, starting from 0:


Note, there is no /-/ separator after a group UUID. It's required for transformations only.

By the way, you can apply Image Transformations to indivitual files within a group:


You can also group the processed files with the respective operation sequences. When you request a file by its group URL, it'll include all operations before adding to that group. Adding more operations after /-/ will apply them over the existing ones.

Get a group as an archive

Getting a group as an archive is done via the archive group processing operation.

The operation limits are:

  • A total size of uncompressed files ≤ 2 GB.
  • Processing operations will be discarded. Only original files will be archived.

Here's how to get an archived file group:

  • :group_uuid — UUID of a file group you want to get as an archive.
  • :format — the format of that output archive, we support zip and tar.
  • :filename (optional) — output archive filename.

A gallery will display a group of images on a single page. The gallery feature is powered by the Fotorama JavaScript library.

Making a gallery is also based on a group processing operation, gallery. Here’s how it works,


You can customize the layout and behavior of images in a gallery by adding Fotorama options to their URLs. The workflow is pretty much the same as with Image Transformations except for image size, dimensions, and ratio manipulations.


The most common use case with gallery is to embed a collection of images into your page via <iframe>:


Show or Download Images

-/inline/yes/ -/inline/no/

By default, CDN instructs browsers to show images and download other file types. The inline control allows you to change this behavior.


File Information

Get file info as JSON


Returns file-related information, such as image dimensions or geotagging data in the JSON format.


In the second option, json response will contain the original key with the info on your original image.

Get file info as application/javascript


Same as the example above, but it returns data as the application/javascript type. Callback name should always be uploadcare_callback. It should receive the two following arguments: id and a response object. For original files, id is na equivalent to their UUIDs. For processed files, id is an equivalent to their URLs, excluding the last operation, jsonp.


In the first case id will be c5b7dd84-c0e2-48ff-babc-d23939f2c6b4, in the second: /c5b7dd84-c0e2-48ff-babc-d23939f2c6b4/-/preview/.

Perceptual hash

File info response includes a value of a perceptual hash calculated using pixel contents of an image. Perceptual hashing is a common fingerprinting technique to quickly compare images and find duplicates or similar images.

Uploadcare automatically calculates a 64-bit long perceptual hash value and returns it as a HEX string. In this example, the perceptual hash value is 940f5fd09aa48ddc:

  "id": "1b192edb-212d-401a-ad9b-529047272e1b",

It’s easy to find image duplicates by quickly comparing their perceptual hash values. To find similar images, it's important to compare perceptual hash values bitwise (Hamming distance). A small number of unmatched bits (e.g., up to 8 bits) will correspond to subtle changes in the visual contents, while non-similar images will usually have more than 8 different bits.


Use your own domain for CDN links to your files stored with Uploadcare. By default, all file URLs use domain. By setting a Custom CDN CNAME, the file URLs can use instead.

Depending on your plan, you can connect Uploadcare CDN to your domain or subdomain with a Let’s Encrypt SSL certificate. Enterprise plans let you choose any CDN you prefer.