X-Akamai-Transformed
The HTTP X-Akamai-Transformed response header is an unofficial HTTP header indicating Akamai's edge platform transformed the response content before delivery.
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.
The value follows a structured format encoding the transformation version, the original content size in bytes, and flags indicating which Akamai features were active. Operators use this header to verify Image Manager and content optimization policies are working as expected, and to compare transformed versus original response sizes for performance tuning.
Values
Transformation string
The value is a space-separated string with four components.
The first segment is a version indicator (commonly 9 for
Image Manager transformations, 0 for pass-through). The
second is the original content size in bytes before
transformation, or - when the size is not recorded. The
third is typically 0. The fourth segment contains
pmb=mRUM (Akamai's performance monitoring beacon) followed
by a comma and a number indicating the compression level or
transformation tier applied.
A version prefix of 9l indicates a large resource
processed through Image Manager. A prefix of l alone
indicates a large resource pass-through. A value of
0 - 0 - signals the response passed through Akamai's
edge without content modification.
Example
A response from a website served through Akamai's edge shows Image Manager compressed the content. The original resource was 42,534 bytes, and Akamai applied a tier-2 transformation with performance monitoring enabled.
X-Akamai-Transformed: 9 42534 0 pmb=mRUM,2
A different response shows Image Manager processed the content, but the original size was not recorded. The dash in the second position indicates the size field was omitted. Tier-3 transformation was applied.
X-Akamai-Transformed: 9 - 0 pmb=mRUM,3
A response passed through Akamai's edge without content
modification. The 0 - 0 - value signals no transformation
was applied. This appears when the resource type or
configuration excludes the response from optimization.
X-Akamai-Transformed: 0 - 0 -
Takeaway
The X-Akamai-Transformed header records content transformations applied by Akamai's edge platform, including image compression and content optimization. The value encodes the transformation type, original content size, and active Akamai features.