X-Akamai-Transformed
When Akamai's CDN applies image compression, minification, or format conversion at the edge, the X-Akamai-Transformed unofficial response header records what transformation was applied.
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.
Usage
When Akamai's CDN processes a response, edge servers apply content transformations such as image Compression (via Image Manager), HTML and JavaScript minification, and adaptive media delivery. The X-Akamai-Transformed header records what transformation was applied, giving operators visibility into how the edge modified the original response.
Akamai publishes no documentation for the value format, so the field meanings are known only from observation. Operators use the header's presence as a signal that edge processing touched the response, and compare transformed versus original response sizes for performance tuning where a size field is recognizable.
Values
Transformation string
The value is a space-separated string, typically with four
fields. Akamai does not document the field semantics, and
observed values in the wild show more variation than any
single decoding scheme accounts for, including forms like
9 - 0 pmb=mNONE,1mRUM,2. A few patterns are consistent
across observations. The second field, when numeric, lines
up with a content size in bytes, and - acts as a
placeholder in several positions. Values containing
pmb=mRUM appear on HTML pages from sites running Akamai's
mPulse real user monitoring, consistent with edge script
injection rather than image transformation. The remaining
fields stay opaque without an Akamai statement on their
meaning.
Example
A response from a website served through Akamai's edge
carries a four-field value. The 42534 field lines up with
a content size in bytes, and the pmb=mRUM marker matches
sites running mPulse monitoring. The other fields are
undocumented.
X-Akamai-Transformed: 9 42534 0 pmb=mRUM,2
A different response replaces the size position with a dash placeholder while keeping the same overall shape.
X-Akamai-Transformed: 9 - 0 pmb=mRUM,3
A minimal value appears on other responses, with every field zeroed or replaced by a placeholder. The exact condition producing this form is undocumented.
X-Akamai-Transformed: 0 - 0 -