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Site Accelerator

Speed up your website’s loading time by optimizing your images and common static assets by serving them from our global network of servers.

Jetpack’s Site Accelerator (a.k.a. Jetpack content delivery network or CDN, formerly known as Photon) helps your pages load faster by optimizing your images and serving them alongside static files (like CSS and JavaScript) from our global network of servers.

For general features and FAQs, please see our CDN features here.

Activate Site Accelerator

Site Accelerator is deactivated by default. To activate it, please follow these steps:

  1. In your site’s dashboard, go to Jetpack → Settings → Performance.
  2. In the Performance & speed section, toggle on
Screenshot of the Performance & Speed dashboard in Jetpack.

Once you turn on Site Accelerator, please keep your photos on your server for the CDN to work correctly. We only make copies, and any images that are removed from your server will eventually “expire” and be removed from our CDN.

If you ever turn off Site Accelerator, images will continue to show on your website, they will just start loading from your webhost’s server again instead of ours. Please note that it could take a few minutes for these changes to take place.

Check that Site Accelerator is working

To check if images are loading from the CDN, you can follow these steps:

  1. Wait a few moments and then load your site in a different web browser, to avoid any caching issues.
  2. Check an image’s URL in your browser’s inspector, or open the image in its own tab. The images served from our CDN have URLs that begin https://i0.wp.com, https://i1.wp.com, https://i2.wp.com or similar.
  3. If you do not see i0.wp.com or similar, see our troubleshooting steps below.

How Site Accelerator works

Image load times

Our Image CDN is an image optimization and editing service. We copy your photos and then host them from our servers, alleviating the load on your server and providing faster image loading for your readers.

Static file load times (Asset CDN)

The Asset CDN serves a limited set of static files only from WordPress core, Jetpack, and WooCommerce via our global network of servers. This reduces the load on your server for these specific assets.

  • It does NOT serve: static files from themes, third-party plugins, or custom scripts.
  • If you disable Site Accelerator, only WordPress core, Jetpack, and WooCommerce assets will revert to loading from your local server. Theme and plugin assets are not affected, as they were never served by Jetpack’s CDN.
  • Site accelerator filters the URLs of assets that are loaded with every WordPress page.
  • Site accelerator only acts on assets shipped with WordPress core, Jetpack, and WooCommerce.

What happens when you disable Site Accelerator?

If you turn off Site Accelerator:

  • Images will still load on your site but will no longer be served via Jetpack’s CDN.
  • WordPress core, Jetpack, and WooCommerce assets will switch back to loading from your site’s local server.
  • Theme and plugin files were never served by Site Accelerator. They will continue to load exactly as before.
  • If your site breaks after disabling Site Accelerator, check for:
    • Caching conflicts – Clear your browser and site cache (both plugins and server-side caching)
    • Missing assets – Ensure all theme and/or plugin files exist on your local server.
    • Dependencies – Some themes or plugins might expect assets to load from Jetpack’s CDN. If disabling causes problems, check with the theme or plugin developer.

Allow the Photon User Agent to Ensure Site Accelerator Works

Jetpack’s Site Accelerator (also known as the Image CDN) relies on accessing your images using a special user agent: Photon/1.0. If this user agent is blocked—by a security plugin, server rules, or firewall—Jetpack will not be able to fetch your images, and they will not be served via Site Accelerator.

Common causes of blocking:

  • Security plugins may block the Photon user agent by default.
  • Custom .htaccess rules may include blocks for unknown or bot-like user agents.
  • Firewall settings may filter or deny requests from Photon/1.0

To fix this issue:

  1. Look for .htaccess or firewall rules that may include a line like:
  2. Check any active security or optimization plugins for user agent filtering features.
  3. If present, remove it or adjust the rule to allow Photon/1.0.
  4. If you must use user agent filtering, make sure to allowlist Photon/1.0 and Jetpack requests.
  5. Optionally, allow Jetpack’s IP ranges if server-level filtering is applied.

When this is misconfigured, you may see:

  • Images not loading from i0.wp.com, i1.wp.com, etc.
  • Broken images or timeouts in the browser.
  • A 403 or empty response for requests from Jetpack servers.

Image resizing

Site Accelerator resizes photos by first checking the img element’s width and height attributes and then serving an image resized to those dimensions, or to the width of the containing element (whichever is smaller).

If there is no size set on the element, Jetpack will constrain images to the size indicated when adding the image to a post, or to your theme’s “content width” setting.

Finally, if a content width isn’t set in your theme, then Site Accelerator will default to 1,000px. This is to help ensure that sites are not trying to serve images larger than what the theme intended to be able to display.

We remove the width and height arguments to prevent your images from skewing when the resized image doesn’t have the same dimensions as the original. This is particularly important when you switch from one theme to another, and the new theme might be narrower than the previous one. One of the benefits of this is that we will automatically resize your images so they don’t exceed the width supported by your theme.

Limitations of Site Accelerator

Cache and theme/plugins

  • Site Accelerator will not fetch or process images larger than 50 MB in size.
  • Site Accelerator does not do cache invalidations. Static assets are tied to the public version of WordPress, Jetpack, or WooCommerce that you’re using. For images, if you want to “refresh” an image, you will need to change its file name. Adding random query arguments, commonly known as “cache busters,” will not work.
  • Theme and plugin assets are not supported by Site Accelerator at this time.
  • Themes and plugins can also use the Photon API to transform images using GET query arguments. Developers will find Photon API examples and documentation on developer.wordpress.com.