X-Cache-Group
The HTTP X-Cache-Group unofficial response header identifies which cache group a caching proxy assigned to a response. WP Engine's page cache is the primary sender, using the header to expose its device-detection groups.
Usage
WP Engine's Varnish-based page cache stores separate cached copies of each page per device class. The cache inspects the User-Agent request header, assigns the request to a group, and serves the cached variant belonging to the group. The X-Cache-Group header exposes the assignment, making the classification visible for debugging.
Splitting the cache by device class keeps mobile-specific markup from being served to desktop visitors and vice versa. Each group maintains its own cached copy, so a purge or a cache miss in one group leaves the others untouched.
This header is primarily a diagnostic tool. Developers and operators verify device detection is routing responses into the expected group. When a response ends up in the wrong group, the header makes the misclassification visible without needing to inspect the platform's internal configuration.
Note
The "X-" naming convention for HTTP headers, "X" referring to "experimental", has been deprecated and needs to be transitioned to the formal naming convention for HTTP headers.
Values
Values are labels defined by the caching platform. WP Engine's
device-detection groups are the dominant set observed in the
wild, with normal accounting for the vast majority of
responses.
normal
The normal value indicates a desktop request served from the
default cache group. This is the most common value by a wide
margin.
iphone
The iphone value covers all mobile user agents, and the
response came from the mobile cache group. The group name is
historical rather than iPhone-specific.
ipad
The ipad value indicates the request was classified as
coming from an iPad and served from the iPad cache group.
bot
The bot value indicates the platform identified the client
as a crawler or automated agent and served the bot cache
group.
bot-mobile
The bot-mobile value indicates a crawler presenting a mobile
User-Agent, such as Googlebot Smartphone, served from a
dedicated mobile-bot group.
mobile-maybe
The mobile-maybe value indicates the User-Agent matched a
generic mobile pattern without mapping to a specific device
group.
Other platforms define their own labels. Observed values on
non-WP Engine deployments include site-specific group names
such as content, public, generic, article, and
guest.
Example
A desktop page served from WP Engine's page cache carries the
normal group. Operators confirm the default cache variant
was used.
X-Cache-Group: normal
A request from an iPhone is routed to the device-specific cache group, confirming the platform stores and serves a separate cached copy for iPhone visitors.
X-Cache-Group: iphone
X-Cache: HIT