HTML Filters

Configure HTML optimization filters in mod_pagespeed 1.1. Whitespace removal, comment stripping, attribute elision, DNS prefetch, and resource preloading.

Overview

mod_pagespeed 1.1 includes filters that optimize HTML structure, remove unnecessary content, and add performance hints. Two HTML filters (add_head, convert_meta_tags) are CoreFilters and run by default.

Quick reference

Filter	Core	Description	Safe
`add_head`	Yes	Adds `<head>` if missing	Yes
`convert_meta_tags`	Yes	Converts meta http-equiv to headers	Yes
`collapse_whitespace`	No	Removes excess whitespace	Generally safe
`remove_comments`	No	Strips HTML comments	Generally safe
`elide_attributes`	No	Removes default-value attributes	Generally safe
`remove_quotes`	No	Removes unnecessary attribute quotes	Generally safe
`trim_urls`	No	Shortens absolute URLs to relative	Generally safe
`combine_heads`	No	Merges multiple `<head>` elements	Generally safe
`pedantic`	No	Adds type attributes for HTML4	Generally safe
`insert_dns_prefetch`	No	Adds DNS prefetch hints	Generally safe
`hint_preload_subresources`	No	Adds preload headers	Generally safe
`add_instrumentation`	No	Injects page load timing JS	Test first

IIS syntax

On IIS, use the same filter names with the pagespeed prefix in pagespeed.config (no semicolons):

pagespeed EnableFilters collapse_whitespace,remove_comments

See IIS Configuration for the full file format reference.

CoreFilters

add_head {#add_head}

Adds a <head> element if the HTML lacks one. Several other filters inject content into <head>, so this filter ensures one exists. Runs automatically as a CoreFilter.

convert_meta_tags {#convert_meta_tags}

Reads <meta http-equiv="Content-Type"> and similar tags and adds corresponding HTTP response headers. This helps browsers discover the content type and character encoding earlier in the response. Runs automatically as a CoreFilter.

HTML minification filters

These filters reduce HTML payload size by removing unnecessary bytes.

collapse_whitespace {#collapse_whitespace}

Removes excess whitespace from HTML. Preserves whitespace inside <pre>, <script>, <style>, and <textarea> elements. Never removes whitespace entirely between inline elements.

remove_comments {#remove_comments}

Strips HTML comments from the page. Use RetainComment to keep specific comments matching a wildcard pattern.

Configuration for nginx:

pagespeed RetainComment "*copyright*";

Configuration for Apache:

ModPagespeedRetainComment "*copyright*"

elide_attributes {#elide_attributes}

Removes HTML attributes that are set to their default values. For example, <form method="get"> becomes <form> because get is the default method.

remove_quotes {#remove_quotes}

Removes unnecessary quotation marks around HTML attribute values when the value contains no special characters. Saves a few bytes per attribute.

trim_urls {#trim_urls}

Shortens absolute URLs to relative URLs where the base URL matches the page URL. Reduces HTML payload at the cost of less portable HTML. Disable this filter if you serve the same HTML from multiple domains.

Structural filters

combine_heads {#combine_heads}

Merges multiple <head> elements into one. Only useful for pages that aggregate content from multiple sources, each contributing their own <head> section.

pedantic {#pedantic}

Adds type="text/javascript" and type="text/css" attributes to <script> and <style> elements. This satisfies HTML4 validators. Not needed for HTML5, where these types are the defaults.

Performance hint filters

insert_dns_prefetch {#insert_dns_prefetch}

Adds <link rel="dns-prefetch" href="//example.com"> tags for third-party domains referenced in the page. This allows the browser to resolve DNS for external domains in parallel with page loading, reducing latency for subsequent resource fetches.

hint_preload_subresources {#hint_preload_subresources}

Adds Link: rel=preload HTTP headers for CSS and JavaScript files discovered on previous visits to the same page. Uses the beacon system to collect resource data, so it becomes effective after the first page view.

add_instrumentation {#add_instrumentation}

Injects JavaScript that measures page load time and reports it back to the mod_pagespeed statistics system via the beacon endpoint (/mod_pagespeed_beacon or /ngx_pagespeed_beacon). Enable this filter to get client-side performance data in the admin console histograms.

Test this filter before deploying to production. The injected JavaScript adds a small overhead and sends beacon requests on every page load.