Filter Reference

Complete reference table of all 56 mod_pagespeed 1.1 filters. Names, categories, CoreFilter status, safety ratings, and descriptions at a glance.

Platform syntax

Filter names are the same across all platforms. The directive syntax differs:

Platform	Enable filter	Disable filter
nginx	`pagespeed EnableFilters rewrite_images;`	`pagespeed DisableFilters rewrite_images;`
Apache	`ModPagespeedEnableFilters rewrite_images`	`ModPagespeedDisableFilters rewrite_images`
IIS	`pagespeed EnableFilters rewrite_images`	`pagespeed DisableFilters rewrite_images`

IIS uses the same pagespeed prefix as nginx but without the trailing semicolon. All directives go in pagespeed.config. See IIS Configuration for the full file format reference.

All filters

Filter	Category	Core	OFB	Description	Safe
`add_head`	HTML	Yes	No	Adds `<head>` element if missing	Generally safe
`add_instrumentation`	HTML	No	No	Injects JavaScript to measure page load time	Test first
`collapse_whitespace`	HTML	No	No	Removes excess whitespace from HTML	Generally safe
`combine_css`	CSS	Yes	No	Combines multiple CSS files into one	Generally safe
`combine_heads`	HTML	No	No	Merges multiple `<head>` elements	Generally safe
`combine_javascript`	JavaScript	Yes	No	Combines multiple JS files into one	Generally safe
`convert_gif_to_png`	Image	Yes	Yes	Converts GIF to PNG	Generally safe
`convert_jpeg_to_progressive`	Image	Yes	Yes	Converts large JPEGs to progressive format	Generally safe
`convert_jpeg_to_webp`	Image	Yes	Yes	Converts JPEG to WebP for capable browsers	Generally safe
`convert_meta_tags`	HTML	Yes	No	Adds HTTP headers from `<meta http-equiv>` tags	Generally safe
`convert_png_to_jpeg`	Image	Yes	Yes	Converts PNG to JPEG when no transparency	Generally safe
`convert_to_webp_animated`	Image	No	No	Converts animated GIF to WebP	Test first
`convert_to_webp_lossless`	Image	No	No	Converts PNG/GIF to lossless WebP	Generally safe
`dedup_inlined_images`	Image	No	No	Replaces repeated inlined images with JS reference	Test first
`defer_javascript`	JavaScript	No	No	Defers JS execution until after page load	Test first
`elide_attributes`	HTML	No	No	Removes default-value HTML attributes	Generally safe
`extend_cache`	Caching	Yes	No	Content-hashed URLs with 1-year browser cache	Generally safe
`extend_cache_pdfs`	Caching	No	No	Cache extension for PDF links	Generally safe
`fallback_rewrite_css_urls`	CSS	Yes	No	Rewrites resource URLs in unparseable CSS	Generally safe
`flatten_css_imports`	CSS	Yes	No	Inlines CSS `@import` rules	Generally safe
`hint_preload_subresources`	HTML	No	No	Adds `Link: rel=preload` headers	Generally safe
`in_place_optimize_for_browser`	Image	No	Yes	Browser-specific in-place optimization	Test first
`inline_css`	CSS	Yes	No	Inlines small external CSS into HTML	Generally safe
`inline_images`	Image	Yes	No	Inlines small images as data: URIs	Generally safe
`inline_import_to_link`	CSS	Yes	No	Converts `<style>@import</style>` to `<link>`	Generally safe
`inline_javascript`	JavaScript	Yes	No	Inlines small external JS into HTML	Generally safe
`inline_preview_images`	Image	No	No	Inserts low-quality image placeholders	Test first
`insert_dns_prefetch`	HTML	No	No	Adds `<link rel=dns-prefetch>` for third-party domains	Generally safe
`insert_image_dimensions`	Image	No	No	Adds width and height attributes to `<img>` tags	Generally safe
`jpeg_sampling`	Image	Yes	Yes	Reduces chroma sampling to 4:2:0	Generally safe
`lazyload_images`	Image	No	No	Defers offscreen image loading	Test first
`local_storage_cache`	Caching	No	No	Caches inlined resources in localStorage	Experimental
`move_css_above_scripts`	CSS	No	No	Moves CSS `<link>` above `<script>` tags	Generally safe
`move_css_to_head`	CSS	No	No	Moves CSS `<link>` into `<head>`	Generally safe
`outline_css`	CSS	No	No	Externalizes large inline CSS blocks	Experimental
`outline_javascript`	JavaScript	No	No	Externalizes large inline JS blocks	Experimental
`pedantic`	HTML	No	No	Adds `type` attributes for HTML4 validation	Generally safe
`prioritize_critical_css`	CSS	No	No	Inlines above-fold CSS, defers the rest	Test first
`recompress_images`	Image	Yes	Yes	Lossless image recompression	Generally safe
`recompress_jpeg`	Image	Yes	Yes	JPEG-specific recompression	Generally safe
`recompress_png`	Image	Yes	Yes	PNG-specific recompression	Generally safe
`recompress_webp`	Image	Yes	Yes	WebP-specific recompression	Generally safe
`remove_comments`	HTML	No	No	Strips HTML comments	Generally safe
`remove_quotes`	HTML	No	No	Removes unnecessary attribute quotes	Generally safe
`resize_images`	Image	Yes	No	Resizes images to match `<img>` dimensions	Generally safe
`resize_mobile_images`	Image	No	No	Smaller placeholders for mobile	Test first
`resize_rendered_image_dimensions`	Image	Yes	No	Resizes to rendered dimensions	Test first
`responsive_images`	Image	No	No	Generates `srcset` for multiple resolutions	Test first
`rewrite_css`	CSS	Yes	Yes	Minifies CSS, rewrites embedded URLs	Generally safe
`rewrite_domains`	Caching	No	No	Applies domain mappings to original resources	Test first
`rewrite_images`	Image	Yes	No	Master image optimization (enables sub-filters)	Generally safe
`rewrite_javascript`	JavaScript	Yes	Yes	Minifies JavaScript	Generally safe
`rewrite_javascript_external`	JavaScript	Yes	Yes	Minifies external JavaScript files	Generally safe
`rewrite_javascript_inline`	JavaScript	Yes	Yes	Minifies inline JavaScript	Generally safe
`rewrite_style_attributes`	CSS	No	No	Applies CSS rewriting to inline `style` attributes	Generally safe
`rewrite_style_attributes_with_url`	CSS	Yes	No	Same, only for styles containing `url()`	Generally safe
`sprite_images`	Image	No	No	Combines CSS background images into sprites	Test first
`strip_image_color_profile`	Image	Yes	Yes	Removes ICC color profiles	Generally safe
`strip_image_meta_data`	Image	Yes	Yes	Removes EXIF and other metadata	Generally safe
`trim_urls`	HTML	No	No	Shortens URLs relative to base URL	Generally safe

Notes

Core filters are enabled by default with RewriteLevel CoreFilters. Some image sub-filters (e.g., recompress_images, jpeg_sampling, strip_image_meta_data) are implicitly enabled by their parent filter rewrite_images and are marked Core for that reason. See Filter Selection for the explicit CoreFilters list.
OFB filters are active under RewriteLevel OptimizeForBandwidth, which optimizes resources in-place without rewriting URLs.
“Test first” filters are safe for most sites but can cause issues with specific JavaScript frameworks or CSS patterns. Test on a staging environment before enabling in production.
“Experimental” filters are available but rarely needed. Use only if you have a specific reason.

Deprecated filters

These filters remain available for backward compatibility but target retired or deprecated services:

canonicalize_javascript_libraries —redirects to Google Hosted Libraries CDN
insert_ga —inserts Google Analytics snippet (ga.js is retired)
make_google_analytics_async —targets retired ga.js
make_show_ads_async —targets deprecated AdSense show_ads.js

Platform syntax

All filters

Notes

Deprecated filters

See also