X-CDN
The HTTP X-CDN response header is an unofficial HTTP header identifying which CDN provider served the response.
Usage
The X-CDN header is set by CDN or WAF providers to signal their presence in the delivery chain. Unlike the Server header, which identifies the origin software, X-CDN names the edge network or security service sitting in front of the origin.
The header appears most frequently on responses from Imperva (formerly Incapsula) and its related services. Other CDN providers sometimes set the same header with their own name, making X-CDN a loose convention rather than a standardized field. The value is informational and carries no Caching or routing semantics.
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
CDN provider name
The most common value is a CDN or WAF brand name.
Imperva is the dominant value in the wild, reflecting
sites protected by Imperva Cloud WAF. Other observed
values include Served-By-Zenedge (Zenedge, acquired
by Oracle), Akamai, fastly, and staticcache
(Shopee's internal CDN label).
Boolean indicator
Some implementations set the value to 1 or true,
confirming CDN involvement without naming the provider.
This pattern is less common and provides no identifying
detail.
Example
A response from a site protected by Imperva Cloud WAF includes the provider name directly.
X-CDN: Imperva
A site served through Fastly sets the header to its lowercase brand name. The value format varies by provider since no specification governs the field.
X-CDN: fastly
Zenedge-based configurations use a descriptive string instead of a plain brand name.
X-CDN: Served-By-Zenedge
When the header carries a boolean value, the CDN confirms its presence without disclosing the provider name. Identifying the specific CDN requires checking other headers like Server or Powered-By.
X-CDN: 1
Takeaway
The X-CDN header is a CDN identification marker, most commonly set by Imperva and other edge providers. The value names the serving CDN or confirms CDN involvement with a boolean flag.