X-Cache-Group
The HTTP X-Cache-Group response header is an unofficial header identifying the cache group or tier applied to a response by a CDN or caching proxy.
Usage
CDNs and caching proxies classify responses into cache groups, each with its own set of policies governing how long content is stored, when content is revalidated, and under what conditions content is bypassed. The X-Cache-Group header exposes which group classification the server applied to the response.
The value is a label defined by the server or CDN
configuration. A common value is normal, indicating the
response falls under the default caching policy. Other
deployments define groups such as aggressive for
long-lived assets, or bypass for content excluded from
caching entirely.
This header is primarily a diagnostic tool. Developers and operators verify Cache-Control rules are routing responses into the expected group. When a response ends up in the wrong group, the header makes the misconfiguration visible without needing to inspect internal CDN dashboards.
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 strings defined by the CDN or reverse proxy configuration. Common group names include:
normal
The normal value indicates the response was classified under
the default caching policy. TTLs, revalidation rules, and
storage behavior follow the standard configuration for the
deployment.
aggressive
The aggressive value indicates the response was placed in a
long-lived cache group, often used for static assets like
images, fonts, or versioned JavaScript files where freshness
requirements are relaxed.
bypass
The bypass value signals the response was excluded from
caching entirely. Dynamic responses, authenticated content, or
responses with Cache-Control: no-store typically fall into
this group.
Example
A CDN serving a standard page response labels the response
with the normal group. Operators confirm default TTL and
revalidation rules apply.
X-Cache-Group: normal
A CDN serving a versioned JavaScript bundle applies the
aggressive group, indicating extended caching with a long
TTL and no early revalidation.
X-Cache-Group: aggressive
X-Cache: HIT
Takeaway
The X-Cache-Group header identifies which cache policy group a CDN applied to the response. A diagnostic header making cache classification visible for debugging and configuration verification.