X-SiteId
The HTTP X-SiteId response header is an unofficial header identifying a specific site within a multi-tenant hosting platform.
Note
The X- prefix for non-standard headers is
deprecated per RFC 6648.
Usage
The X-SiteId header is set by shared hosting environments, managed WordPress platforms, and SaaS infrastructure where multiple sites run on common backend systems. The value is a numeric or string identifier uniquely distinguishing which site on the platform generated the response.
When many sites share the same servers, load balancers, and Caching layers, a site identifier in the response header gives operators a way to correlate requests with specific tenants. Server logs, monitoring systems, and debugging tools use the value to filter traffic by site without relying solely on the request domain.
The header carries no semantic meaning to browsers or end users. Its audience is the platform operator and the site owner inspecting response headers for diagnostic purposes.
Values
The value format varies by platform. Numeric identifiers are most common, typically assigned sequentially or randomly at site creation. Some platforms use alphanumeric slugs or UUID-style strings instead.
Example
A response from a shared hosting platform where site 4827 generated the request. The numeric value maps to a specific tenant account in the platform's internal database.
X-SiteId: 4827
A platform using an alphanumeric identifier to distinguish sites.
X-SiteId: prod-site-abc123
Takeaway
The X-SiteId header identifies which site within a multi-tenant platform produced the response. The value is an internal identifier used for log correlation and debugging in environments where multiple sites share infrastructure.