PageSpeed markers reference

Excludes a <script> from the defer_javascript filter, so that script runs during page load instead of being deferred to onload.

When you see it: You add it by hand to a script that must execute inline — for example a script that other inline code depends on, or one that writes to the page before load. The deprecated spelling is pagespeed_no_defer; the combine_javascript filter also leaves scripts carrying it alone. The lazyload_images filter honors the same attribute on an <img> to leave that image eagerly loaded.

<script data-pagespeed-no-defer>
  // runs in place, not deferred to onload
</script>

Tells the image filters to leave a specific element alone — no recompression, no resizing, no srcset injection.

When you see it: You add it to an <img> (or other element) you want delivered exactly as authored — a pixel-perfect asset, a tracking pixel, or an image another script measures. The legacy spelling is pagespeed_no_transform. The element may still be cache-extended.

<img src="logo.png" width="160" height="40" data-pagespeed-no-transform>

Disables optimization for a single request, so the origin response is served unrewritten. ?PageSpeed=on forces it back on.

When you see it: You append it while debugging to compare optimized vs. unoptimized output for one URL. On Apache the equivalent legacy spelling is ?ModPagespeed=off. These three values — on, off, and noscript — are honored without a token; any other query-parameter override requires the RequestOptionOverride token configured on the server.

https://example.com/page.html?PageSpeed=off

The no-JavaScript fallback URL. Filters that inject client-side JavaScript also inject a <noscript> meta-refresh that redirects no-JS browsers to this variant, which serves the page without the JS-dependent rewrites.

When you see it: You see ?PageSpeed=noscript (or ?ModPagespeed=noscript) in your address bar after landing on a page with JavaScript disabled, or in the injected <noscript> block in page source. The filters that add it include lazyload_images, inline_preview_images, inline_images, and prioritize_critical_css. The SupportNoScript option controls whether the <noscript> block is inserted.

<noscript>
  <meta http-equiv="refresh" content="0;url='/page.html?PageSpeed=noscript'">
</noscript>

The naming scheme for rewritten static assets. The two-letter code identifies which filter produced the resource; the hash is a content hash that lets the module cache-extend the URL with a long max-age and still invalidate it when the bytes change.

When you see it: You see these in page source and the network tab in place of the original CSS, JS, and image URLs. The shape is original-name.pagespeed.<code>.<hash>.<ext>. Common codes: ic = image recompress/resize, ce = cache extend, jm = JavaScript minify, cf = CSS rewrite/minify, jc = combine JavaScript, cc = combine CSS.

logo.png.pagespeed.ic.GpQ1A7n5Kz.png
site.css.pagespeed.cf.j7l9m2Xp4Q.css
app.js.pagespeed.jm.kZ3w8tRq1Lp.js

The instrumentation beacon endpoint. JavaScript injected by certain filters reports measurements to it: page-load timing from add_instrumentation as a GET, and which images and CSS are above the fold from the critical-image and critical-CSS beacons as a POST.

When you see it: You see requests to /mod_pagespeed_beacon (Apache) or /ngx_pagespeed_beacon (nginx) in your access log or network tab. The default path is set by the ModPagespeedBeaconUrl directive. The data feeds the optimizer: it learns the critical viewport and prioritizes those images and CSS on later requests.

GET /ngx_pagespeed_beacon?ets=load:312  →  204

Holds the real image URL while the lazyload_images filter is active. The filter rewrites <img src> to data-pagespeed-lazy-src and swaps it back in JavaScript once the image scrolls near the viewport.

When you see it: You see it on <img> tags in rendered source when lazyload_images is enabled. If images are not loading and you have JavaScript disabled, this is why — the no-JS fallback above (?PageSpeed=noscript) exists to serve those images normally.

<img data-pagespeed-lazy-src="/photo.jpg" src="/data:image/gif;base64,...placeholder...">

A hash of an image’s original URL, written onto <img> tags by the critical-image beacon. It lets the beacon report which images were in the initial viewport without the client knowing anything about the module’s URL rewriting.

When you see it: You see it alongside the beacon machinery when critical-image beaconing is on. It is bookkeeping for the optimizer, not something you set — the server matches the reported hash back to the original image to learn what was above the fold.

Identifies the module and its version on every response it touches. nginx and IIS emit X-Page-Speed; Apache emits X-Mod-Pagespeed.

When you see it: You see it in response headers when the module is active. Use it to confirm an optimizer is in the request path and which version is running. The header text is configurable via the XHeaderValue directive.

X-Page-Speed: 1.15.0.0