Is trim_urls enabled by default?

No. trim_urls is not in CoreFilters, the default RewriteLevel; it runs only when you enable it by name with EnableFilters.

How do I enable trim_urls on Apache and nginx?

Add ModPagespeedEnableFilters trim_urls on Apache or pagespeed EnableFilters trim_urls; on nginx. On IIS, add pagespeed EnableFilters trim_urls to pagespeed.config.

filter · HTML filters

Trim URLs (trim_urls)

Q: What does the trim_urls filter do?

trim_urls shortens URLs inside the page by stripping the parts that repeat the page's own origin. An absolute URL whose scheme, host and port match the page loses its origin, and the page's own directory prefix is trimmed too; URLs on any other origin, including the same host over another scheme, are left untouched. left_trim_urls is an accepted alternate spelling of the same filter; both names switch on the same code.

Category:: HTML
CoreFilters:: No
OptimizeForBandwidth:: No
Risk:: Generally safe

trim_urls shortens URLs inside the page by stripping the parts that repeat the page’s own origin. An absolute URL whose scheme, host and port match the page loses its origin, and the page’s own directory prefix is trimmed too; URLs on any other origin, including the same host over another scheme, are left untouched. left_trim_urls is an accepted alternate spelling of the same filter; both names switch on the same code.

How it works

Live demo: trim_urls.

When it helps and when it does not

It saves a few bytes per URL on pages dense with same-origin absolute links, which is typical of CMS output that expands every URL in full; under gzip or Brotli the saving shrinks further, since the repeated origin strings compress well. It does not help pages that already use relative URLs throughout. Keep it off for HTML that lives beyond its origin: a saved page, an emailed copy, or markup served under a second domain resolves relative URLs against the wrong base.

How it decides

Each URL-valued attribute is resolved against the page’s base URL, and a <base> tag wins when present and is never itself rewritten. Only what matches gets trimmed: a full origin match drops the origin, a path under the page’s own directory then drops that directory as well, and a URL on another origin keeps its full form. A trim is kept only when the shorter URL resolves back to exactly the original one.

When to use it

Not in CoreFilters: it runs only when you enable it by name.
Risk rating on these docs: Generally safe.

Risks

Serving the same cached HTML from multiple domains, or any flow that detaches the markup from its origin, turns the trimming into broken links; disable trim_urls for that content.
Verify with the X-Mod-Pagespeed response header and a ?PageSpeedFilters=-trim_urls comparison; Is it working? has the steps.

Configuration

Enable it in the module configuration, at server, virtual-host or location scope:

Apache

ModPagespeedEnableFilters trim_urls

nginx

pagespeed EnableFilters trim_urls;

IIS (pagespeed.config)

pagespeed EnableFilters trim_urls

<!-- page: https://example.com/shop/ -->
<!-- before -->
<a href="https://example.com/shop/cart">Cart</a>
<img src="https://example.com/img/logo.png" />

<!-- after -->
<a href="cart">Cart</a>
<img src="/img/logo.png" />

Scoping, ForbidFilters and the thresholds filters read: Choosing filters .

Live example

Shortens resource URLs to relative form where it is safe to do so.

Measured on the demo page, original against optimized:

HTML size

147 B → 124 B −16%

See the before and after, with the source diff →

Frequently asked questions

What does the trim_urls filter do?: trim_urls shortens URLs inside the page by stripping the parts that repeat the page's own origin. An absolute URL whose scheme, host and port match the page loses its origin, and the page's own directory prefix is trimmed too; URLs on any other origin, including the same host over another scheme, are left untouched. left_trim_urls is an accepted alternate spelling of the same filter; both names switch on the same code.
Is trim_urls enabled by default?: No. trim_urls is not in CoreFilters, the default RewriteLevel; it runs only when you enable it by name with EnableFilters.
How do I enable trim_urls on Apache and nginx?: Add ModPagespeedEnableFilters trim_urls on Apache or pagespeed EnableFilters trim_urls; on nginx. On IIS, add pagespeed EnableFilters trim_urls to pagespeed.config.

left_trim_urls — Trim URLs
rewrite_domains — Rewrite domains
extend_cache — Extend cache
add_base_tag — Add base tag
add_head — Add head
add_ids — Add IDs
add_instrumentation — Add instrumentation
collapse_whitespace — Collapse whitespace

This page is drawn from the trim_urls entry on HTML filters. Every filter in one table: PageSpeed filters.