X-Vercel-Id
The HTTP X-Vercel-Id response header is an unofficial HTTP header containing a request identifier assigned by Vercel's edge network.
Note
The X- prefix for non-standard headers is
deprecated per RFC 6648.
Usage
Vercel adds the X-Vercel-Id header to every response passing through its edge network. The value encodes the regions the request passed through and a unique identifier for the request. This makes tracing a single request across Vercel's infrastructure straightforward.
The header also serves as an infinite loop prevention mechanism. When Vercel sees its own X-Vercel-Id on an incoming request, the platform detects a routing loop and stops the request before the loop continues.
Values
region
The region code at the start of the value identifies the
Vercel edge location handling the request. Vercel uses
short region identifiers like iad1 (Ashburn, Virginia),
sfo1 (San Francisco), cdg1 (Paris), lhr1 (London),
bom1 (Mumbai), and fra1 (Frankfurt). These correspond
to Vercel's global edge network locations.
request-id
The request identifier is a unique string following the region code. The format combines a short alphanumeric node identifier, a Unix timestamp in milliseconds, and a hex-encoded hash, separated by hyphens. Each request gets a distinct identifier for log correlation and debugging.
Example
A request served by the Ashburn, Virginia edge location
(iad1). The identifier after the :: separator encodes
the node, timestamp, and a unique hash for the request.
X-Vercel-Id: iad1::d4285-1769280933622-449e98882f00
A request routed through San Francisco (sfo1). Different
regions appear in the header depending on which edge
location is closest to the client.
X-Vercel-Id: sfo1::hmvhs-1771412927491-912582182ea4
When a request passes through multiple regions, the header
lists each region separated by ::. In this case, the
request entered through San Francisco (sfo1) and was
forwarded to Ashburn (iad1) where the function executed.
X-Vercel-Id: sfo1::iad1::4f7bd-1767573844669-3e8b87bee054
Takeaway
The X-Vercel-Id response header identifies the Vercel edge regions involved in handling a request and attaches a unique identifier for tracing and debugging purposes.