In short. Read x-vercel-cache for CDN status, inspect request headers for domain and deployment context, and use runtime logs to review crawler response details.
Definition: Vercel response header inspection means reading the metadata returned with a deployment's HTTP response. As of 17 October 2026, Vercel documents
x-vercel-cachefor content delivery network (CDN) cache status andx-vercel-idfor the regions involved in handling a request.
Key facts
- Vercel's System Headers documentation distinguishes headers received with a request from headers returned with a response.
- The response header reference identifies
x-vercel-cacheas a CDN indicator; a runtime data cache can still supply data when that header readsMISS. - The cache status reference defines
BYPASSas deliberately skipping the cache and serving fresh content. - The runtime logs documentation provides separate filters for Cache and Status Code.
Where are the headers visible?
Vercel's response header reference documents browser developer tools and this command, with the deployment URL substituted for the placeholder:
curl -I <DEPLOYMENT_URL>
The x-vercel-id value includes the Vercel regions reached by the request and the function execution region. The content-type field describes the response's media format.
Vercel's request header reference documents reading incoming headers through the function's Request object. For deployment diagnosis, host identifies the domain requested by the client, while x-vercel-deployment-url identifies the underlying deployment. These are useful fields when comparing a production domain with a deployment URL.
What does each cache status mean?
The cache status documentation defines the values returned in x-vercel-cache:
HITmeans a stored response serves the request.MISSmeans the function or origin generates the response after an unsuccessful cache lookup.BYPASSmeans Vercel deliberately skips that lookup.STALEmeans an older cached response is served during a background refresh.PRERENDERmeans the response comes from static storage.REVALIDATEDmeans a deleted cache entry requires foreground regeneration.
The same documentation describes a crawler-specific bypass reason: on a path with a prerender fallback, Vercel can wait for the complete page for a matching crawler. A cache bypass therefore has a documented rendering use.
Why can the visible cache policy differ?
Vercel's Cache-Control documentation gives its CDN this priority order when multiple policy headers are present:
Vercel-CDN-Cache-Control
CDN-Cache-Control
Cache-Control
The proxy consumes Vercel-CDN-Cache-Control before sending the response to the client. When Cache-Control is the only cache policy header, Vercel removes its s-maxage directive before forwarding it. Consequently, inspecting the client response needs to be paired with reviewing the policy set by the application.
How are crawler responses checked in logs?
Vercel's runtime logs reference documents Request Path, Request Method, Host and Deployment filters. Its request details include Request User Agent and Firewall, which shows whether the request passed the firewall. Reviewing those details alongside the HTTP status and cache result helps distinguish access handling from cache handling for a recorded request.
Related terms
- Cache-Control
- HTTP status codes
- How do I filter Vercel runtime logs for a function request?
- Where do I manage AI bot access in Vercel?
FAQ
Does MISS mean my page failed?
Vercel's cache status reference describes misses as expected for dynamic routes generated on each request. You can inspect the response's HTTP status separately.
Which field helps me distinguish the requested domain from the deployment?
Vercel's request header reference documents host for the domain accessed and x-vercel-deployment-url for the underlying deployment. You can read both in the function's incoming Request object.
Sources
- Vercel, "System Headers", 11 August 2026
- Vercel, "Response headers", 11 August 2026
- Vercel, "Request headers", 13 December 2025
- Vercel, "Cache Status and Reasons", 15 September 2026
- Vercel, "Cache-Control headers", 14 September 2026
- Vercel, "Runtime Logs", 28 August 2026
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