The site accelerator is the Content Delivery Network (CDN) on WordPress.com, optimized to speed up your site by delivering faster images and static files. In this guide, you will learn about the site accelerator, how to enable it on your website, and the limitations of a CDN.
In this guide
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Ask our AI assistantThe site accelerator CDN is enabled by default on WordPress.com sites, with the ability to turn it on or off on higher-level plans:
- Visit your site’s dashboard.
- Navigate to Jetpack → Settings.
- Click on the tab labeled “Performance”.
- Locate the “Performance & speed” section.
- Toggle the option next to “Enable Site Accelerator” and enable the following settings:
- Speed up image load times: We host your images from our servers, providing faster image loading for your readers.
- Speed up static file load times: We host static assets like JavaScript and CSS from our servers, alleviating the load on your site.
The site accelerator only works with publicly available images. If your site is set to private, turning on the “Speed up image load times” setting will cause images, including those in your media library, to return a 403 Forbidden error.
To check if your images are loading from the CDN, follow these steps:
- Wait a few minutes after enabling the feature, then open your site in a different browser or incognito window to avoid cached results.
- Right-click an image and inspect its URL using your browser’s developer tools, or open the image in a new tab.
- If the image is being served from the CDN, the URL will start with something like
https://i0.wp.com,https://i1.wp.com, orhttps://i2.wp.com.
The site accelerator is a collection of tools to help improve the performance of your WordPress.com site:
The image CDN speeds up image delivery to your visitors and reduces server load times. It works by creating copies of the images you upload and storing them on WordPress.com servers, allowing your site to load images faster without relying on your site’s main server.
The site accelerator applies to old and new posts and can be turned on or off easily, applying the changes in just a few minutes. It serves WebP image data to browsers that support the WebP image format (note that the file extension won’t change).
The site accelerator improves image performance by resizing images based on the img element’s width and height attributes, or the width of the containing element—whichever is smaller.
If no size is set on the image, the CDN uses the dimensions selected when the image was added to a post, or falls back to the theme’s defined content width. If the theme doesn’t define a content width, the site accelerator defaults to 1000px to prevent oversized images from being served.
To avoid distortion, the width and height attributes are removed when the resized image doesn’t match the original proportions. This is especially helpful when switching themes, as images will automatically adjust to fit the new layout without manual updates.
To speed up page load times with parallel downloads, the site accelerator uses multiple subdomains: i0.wp.com, i1.wp.com, and i2.wp.com. If your pages include many images, spreading them across these subdomains can improve performance. For better caching, it’s best to use the same subdomain for repeated image requests.
The site accelerator works on secure (HTTPS) pages without triggering mixed content warnings. Simply use https://i0.wp.com, https://i1.wp.com, or https://i2.wp.com when referencing images.
The asset CDN serves static files, such as JavaScript and CSS from WordPress core, Jetpack, and WooCommerce, from WordPress.com’s servers. This helps reduce the load on your site’s server and improves overall performance.
The site accelerator filters the URLs of assets that are loaded with every WordPress page. It acts only on assets shipped with WordPress core, Jetpack, and WooCommerce.
If you’ve enabled the site accelerator and your images appear broken, try the following steps:
- Wait a few minutes, then open your site in a different browser to rule out any caching issues. It can take a little time for the changes to take effect across your site.
- Make sure your Jetpack connection is working correctly.
- Temporarily disable all plugins except Jetpack and check your images again. If they display correctly, another plugin may be causing the issue. Re-enable your plugins one by one, checking the images after each, to identify the source of the conflict.
- If the issue persists, try switching to a default theme like Twenty Twenty-Four. If that fixes the problem, the conflict is likely theme-related, and you may want to reach out to the theme’s developer for support.
The site accelerator does not support cache invalidation. Static files are tied to the public versions of WordPress, Jetpack, or WooCommerce in use. For images, if you need to refresh or update a file, you must rename it. Adding query strings (also known as cache busters) will not force an update.
Assets loaded from third-party themes or plugins are not served through site accelerator.
There is no way to automatically purge all images from the site accelerator. If an image has been removed from your server but still appears via the CDN (e.g., from i0.wp.com, i1.wp.com, etc.), you can contact support with the direct image URL. Keep in mind that images can only be removed one at a time, so there is a limit to how many we can process.
The site accelerator only handles .gif, .png, .jpg, and .webp images from servers listening on port 80 (HTTP) or port 443 (HTTPS), which includes nearly all web servers. If you’re having trouble, you can try using the jetpack_photon_reject_https filter.
The site accelerator will not enlarge images beyond their original size. For example, if your original image is 1000px wide and you request it at 5000px, it will still be served at 1000px to maintain quality.
Filters that require significant processing (such as brightness, contrast, colorize, or smooth) will not be applied to large images.
If your server takes more than 10 seconds to respond when the CDN tries to retrieve an image, the request will time out and the image may appear broken. To fix this, try uploading a smaller or renamed version of the file.
You cannot control or restrict which global CDN location serves your images. Our system automatically chooses the most efficient server based on the visitor’s location and other factors.
Animated PNG files are not supported by the site accelerator.
The site accelerator does not serve media files like .mp3, .wav, .mp4, or similar formats. If you want to host video content on our CDN, consider using VideoPress.
