Everything you need to know about how Filestack delivers your content.


Filestack leverages a CDN to ensure fast and reliable global access to your assets. The CDN is used to access all files that are managed by your Filestack application. This is the base URL for all assets on the Filestack CDN; a file can be accessed by appending its handle:


Filestack’s CDN caches Filestack URLs the first time they are accessed, such as in the case of storage aliases or transformations. The cached copy of any unique Filestack URL will live for 30 days – it will then be re-cached only when it is requested again.

If desired, you can bypass the cache (retrieve a file directly from its storage location) by adding the /cache=false/ task to your URL: /cache=false/ HANDLE

If you would like to explicitly control how long the file stays cached, you may specify an expiry in seconds: /cache=expiry:VALUE/ HANDLE

You can find more information about the /cache/ task in the Processing API reference.

NOTE 1: Files are cached based on their associated unique URLs. Adding an expiry will only affect that specific URL. Security policies and signatures are excluded when determining URL uniqueness.

NOTE 2: If your files are not accessed frequently they can be purged from the CDN regardless of your expiry settings.

Responsive Images

Use Filestack’s adaptive library to generate HTML picture elements using your assets and powered by the Filestack CDN. The picture element is part of the latest HTML specification, and it lets the browser decide what kind of images to request based on viewport information and user-defined breakpoints. It can also be used to request WebP images whenever the browser supports it.

You can use adaptive to ensure that smaller files are requested for smaller screens, thus improving site load times and user experience.

Custom CNAME

Custom CNAME is a premium feature that allows you to format Filestack URLs with a custom origin. This means you can replace the base Filestack domain with a fs subdomain on your own fully qualified domain name:

So this…

Becomes this:


This can be useful if you expose your Filestack URLs to customers or need all of your assets to be derived from the same origin.

It requires that we add your domain to our managed wild-card SSL certificate in the Filestack CDN, and that you add the required DNS records for each Filestack service you intend to use.

The custom CNAME works for delivery and also for ingress traffic, such as when making requests to our API endpoints. For instance, you can configure the JavaScript API client to use your CNAME for all outgoing requests by setting the client’s cname option:

const options = { cname: '' };
const client = filestack.init('apikey', options);

Please contact sales if you would like to set up a custom CNAME for your application.