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 Enable Site Accelerator.

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.

• Site Accelerator filters content but doesn’t change your database.
• Site Accelerator acts on images in posts and pages, as well as featured images/post thumbnails via the image_downsize filter. Examples of WordPress functions using the image_downsize filter:
  • the_post_thumbnail_url
  • get_the_post_thumbnail
  • get_the_post_thumbnail_url
  • wp_get_attachment_image
  • wp_get_attachment_image_src
• Site Accelerator will apply to old and new posts alike and can be turned on or off easily, applying the changes in just a few minutes total.
• Browsers that support the WebP image format will be served WebP image data (note that the file extension won’t change).

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.

Self-served image purge

It is not possible to automatically purge or delete all cached site images from Jetpack servers.

If there is an image that is no longer on your server and you’d like us to remove it, please contact Jetpack support with a direct link to the file as it appears on your site. Cached image links usually begin with i0.wp.com, i1.wp.com, i2.wp.com, or i3.wp.com.

Since images can only be purged or deleted manually by individual URL, there is a limit to how many we can remove. Bulk purges or whole-site deletions for cached images are not possible.

Size edit, and type of files

• We will not “upscale” an image in most circumstances. If your original image is 1,000px wide and you ask for Jetpack to make it 5,000px, we will serve the original 1,000px image. Upscaled images are usually of poor quality, and we want to avoid that.
• Site Accelerator only handles GIF, PNG, JPG, and WebP images from servers that listen on port 80 for HTTP and port 443 for HTTPS. This applies to about 99.99% of the web servers in the world. If you are having issues, please try using the jetpack_photon_reject_https filter.
• Site Accelerator does not support animated PNGs.
• Site Accelerator does not serve audio (.mp3, .wav, .flac, etc.) or video (.mp4, .wmv, .flv, etc.) files. If you’d like to host videos on our CDN, check out our Video Hosting feature.

Server time out and serving image location

• If your server takes longer than 10 seconds when an image is being retrieved for our CDN, the process will time out and your image will appear to be broken. Try to upload a differently-named image with a smaller dimension or file size if this happens.
• It’s not possible to choose or limit where in the world your images will be served from. We have servers placed all over the world, and which server will load your image is dependent on a variety of factors, including the visitor’s location.

Site Accelerator is only allowed to be used by sites hosted on WordPress.com or on Jetpack-connected WordPress sites. If you move to another platform or disconnect Jetpack from your site, please also switch to another image CDN service. Any abuse of Jetpack or violation of the WordPress.com Terms of Service could result in the suspension of your site from WordPress.com-connected services, including Site Accelerator.

Troubleshooting Site Accelerator

My images don’t load

1. Wait a few minutes and reload your site in an incognito/private browsing window. It may take time for changes to apply.
2. Right-click an image and open it in a new tab. If the URL doesn’t start with i0.wp.com, i1.wp.com, or similar, image acceleration isn’t active.
3. Make sure Jetpack is properly connected to WordPress.com.
4. Some image optimization plugins may conflict with Site Accelerator by altering image URLs or introducing lazy loading mechanisms. Disable all other plugins except Jetpack and check if the issue resolves. If images display properly, re-enable plugins one by one to identify the conflicting plugin.
5. If images still aren’t loading, switch to a default WordPress theme (e.g., Twenty Twenty-Four) to check for a theme conflict.

The static assets don’t load after disabling Asset CDN

1. Clear your browser cache and site cache to remove any outdated references to Jetpack’s CDN.
2. Check if the missing files exist on your local server. If they’re missing, try reinstalling WordPress core, Jetpack, or WooCommerce. If the issue persists, check for incorrect file paths or conflicts with caching plugins.
3. If using a caching plugin, purge the cache and reload your site. Some plugins may still be referencing the old CDN URLs.
4. Disable all other optimization plugins and test again. Some caching/minification tools may interfere with asset delivery.
5. If issues persist, temporarily re-enable Site Accelerator and check if the problem is resolved. This helps confirm whether the issue is related to disabling the CDN.

Site Accelerator and User Agent Filters

Site Accelerator requires Jetpack to access your images using a specific user agent, Photon/1.0. If this user agent is blocked by a plugin, firewall, or server configuration, Jetpack will not be able to retrieve or cache your images. This prevents Site Accelerator from functioning correctly.

Why this matters

Jetpack’s Site Accelerator fetches and optimizes images directly from your server. This process depends on the `Photon/1.0` user agent being allowed. If it’s blocked, Jetpack cannot deliver your images via its CDN even if the feature is enabled.

Signs that the Photon user agent may be blocked

1. Images are not loading from Jetpack CDN domains like i0.wp.com, i1.wp.com, etc.
2. You see 403 or timeout errors in your browser’s network tools.
3. Site Accelerator appears enabled but has no visible effect on image delivery.

How to check for and resolve user agent blocks

Check for plugin, firewall, or server rules that may be filtering or blocking user agents. Security tools like Blackhole for Bad Bots or WP-Optimize have been known to interfere with Jetpack in this way.

To verify, look for code similar to the following in your .htaccess file:

# Block Photon
RewriteEngine On
RewriteCond %{HTTP_USER_AGENT} Photon/1.0 [NC]
RewriteRule .* - [F,L]

If this rule is present, Site Accelerator will not be able to access your images. You’ll need to remove or modify the rule to allow the Photon/1.0 user agent.

If you use stricter user agent filtering, we recommend allowlisting Photon/1.0 and optionally Jetpack’s IP ranges to avoid unintended blocking.

We provide this example for reference only. Per our Scope of Support, we cannot assist with implementing or troubleshooting custom server rules.

Privacy Information

Site Accelerator is deactivated by default. You can toggle the feature on or off under the Performance & speed section from Jetpack → Settings → Performance in your dashboard.