Experimenting with PageSpeed
The Run Experiment module allows you to gather data on what filters perform best for your site using A/B testing. It reports to your Google Analytics account, storing data in a custom variable. It often makes sense to first experiment manually using the per-request configuration described below to get an idea of which filters might help your site, and then run a controlled experiment to test whether these filters actually speed it up in practice.
Query parameters, request headers, and response headers can be used to disable PageSpeed, specify the set of filters applied to an HTML page, and control some inlining limits.
Query parameters take the form of
and parameters are separated by an ampersand (&). For example:
Request and response headers take the form of
and each header is on its own line. For example:
GET /rewrite_css.html HTTP/1.1 Host: modpagespeed.com PageSpeed: on PageSpeedFilters: rewrite_css
For backwards compatibility, these can start with
PageSpeed, but this usage is deprecated.
Query parameters can be added to the URL of the page or resource being fetched, request headers can be set in the request for pages and resources, and response headers can be set in the response of HTML pages (but not resources). These settings affect only the given request. If all three (query parameters and both headers) are used in the same request the query parameters will be applied first, followed by the request headers, followed by the response headers. Later settings override earlier settings but a filter disable in any location always overrides subsequent enables.
There are two supported methods of adding response headers that PageSpeed will be able to observe and process. The first is to add response headers with a content handler such as PHP or Perl. The second is to add response headers at an origin server and run PageSpeed as a proxy in front of it. The use of mod_headers (Apache) or add_header (Nginx) on the same webserver as PageSpeed will not work because headers will be inserted after PageSpeed has already processed the page.
Sticky Query Parameters
Query parameters can be set to be "sticky" and persist across requests using cookies. Sticky query parameters can be set by providing the sticky query parameter option in a request, and the server will respond with a cookie, valid for the duration specified in the PageSpeed configuration.
To prevent abuse, a "secret token" must be provided in the initial request to enable setting cookies.
pagespeed StickyQueryParameters example_token
The duration, in milliseconds, for which the cookie will be valid can be set in the PageSpeed configuration.
pagespeed OptionCookiesDurationMs 12345
The request must specify the token in a query parameter, for example:
A request with the proper sticky query parameter token will cause the server to
respond with a
Set-Cookie in the response.
Any request not containing the correct token will not receive the
Set-Cookie response. Future responses with the received cookie will
also enable the options set in the query parameter with the sticky query
parameter. In this case, the
remove-comments filter would be
Enabling and disabling PageSpeed
Request & Response headers:
PageSpeed: off PageSpeed: on
The first line disables PageSpeed rewriting, the second line enables it.
Specifying the filters applied
PageSpeedFilters=comma-separated list of names
Request & Response headers:
PageSpeedFilters: comma-separated list of names
This specifies the set of filters to apply to the page. The list of settings includes all filter names and a few shortcut names:
coresets the rewrite level (per
CoreFilters. This enables the core set of filters.
testingenables all filters that are in the
TestingCoreFilterslevel but are not in the
CoreFilterslevel - this is not the same as setting the level to
TestingCoreFiltersbecause that includes all core filters, but the same effect can be achieved by specifying both:
rewrite_imagesenables the following filters:
extend_cacheenables the following filters:
When any filter is specified without a "
-", any filters not explicitly enabled are
disabled. Filters and shortcuts can be explicitly disabled by
preceding the name by a minus sign ('-'), which is useful
after using a shortcut. For example,
core,-combine_css" enables all the core
If all names are prefixed with "
+" or "
-" then the
filter set is incrementally adjusted from the current system settings based on
the configuration files. For example, in a server
RewriteLevel set to
CoreFilters, the query-string
will leave all the core filters enabled, but will add lazyload_images and disable inline images.
Controlling inlining limits
PageSpeedCssFlattenMaxBytes=value PageSpeedCssImageInlineMaxBytes=value PageSpeedCssInlineMaxBytes=value PageSpeedImageInlineMaxBytes=value PageSpeedJsInlineMaxBytes=value
Request & Response headers:
PageSpeedCssFlattenMaxBytes: value PageSpeedCssImageInlineMaxBytes: value PageSpeedCssInlineMaxBytes: value PageSpeedImageInlineMaxBytes: value PageSpeedJsInlineMaxBytes: value
These specify the limits for the following inlining options:
PageSpeedCssFlattenMaxBytessets the maximum size of CSS files that will be flattened.
PageSpeedCssImageInlineMaxBytessets the maximum size of images inside CSS. For inline CSS in HTML files, the value used is the smaller of this value or
PageSpeedCssInlineMaxBytessets the maximum size of CSS files that will be inlined.
PageSpeedImageInlineMaxBytessets the maximum size of image files that will be inlined.
Client options in queries and headers
This is an experimental option, its name and values are subject to change. This option allows the client to customize the optimizations applied to a request and can be used in a header or query parameter.
As a query parameter:
As a Request or Response header:
The format of client-options is
The order of the name-value pairs does not matter. The supported options are:
Version of the header. '1' is the only supported version for now.
Mode. Valid values are
0, the client prefers that the server operates in its default mode.
1, the client prefers that no image is transformed.
2, the client prefers that no resource is transformed. This is equivalent to "?PageSpeedFilters=" in the request URL
Image quality preference. Valid values are
0, the client prefers that the server uses its own default image quality.
1, the client prefers low image quality.
2, the client prefers medium image quality.
3, the client prefers high image quality.
Restrict per-request configuration
Note: New feature as of 220.127.116.11
Interpretation of PageSpeed query parameters and headers can be restricted to requests specifying a request option override token. The token is specified in the server configuration file and disallows request option overriding when the request does not specify the correct token. This option can be used to reduce the attack surface of denial of service attacks.
pagespeed RequestOptionOverride example_token
This feature provides a mechanism to restrict the ability for filters and
options to be specified in query parameters and request headers.
To enable it, an override token must be specified in the configuration file,
and requests must specify the same token for filters and options to be
Query parameters, except for
PageSpeed=noscript will then only
be interpreted when accompanied by the correct
RequestOptionOverride token. For example, the rewrite_css filter
would be used in this example.
The request must specify the token in a query parameter or header, for example:
Any request not containing the correct
token or not containing a
RequestOptionOverride token will ignore
all other PageSpeed filters and options specified.
Note: even if applied, PageSpeed=on/off/noscript still takes effect.
Note: New feature as of 18.104.22.168
To help bust browser caches, especially with experiments, any
PageSpeed URL can accept the
PageSpeedNoop query-paramter with an integer value. This
query-parameter will be ignored by PageSpeed and stripped from the
URL early in the processing flow. The origin will not see the
parameter, and PageSpeed's server-caches will not be affected. However, it
will prevent your browser from using a cached value.