Provides timing information for cached resources.

Fastly writes this header into responses. It is proprietary to Fastly.

When Fastly-Debug is present in a request, this header is attached to the response and contains information on various timings.

Fastly-Debug-TTL: H cache-jfk1026-JFK 41733294.335 864000.000 2273

The syntax is:

{cacheStatus} {serverIdentity} {remainingTTL} {staleIfErrorTTL} {age}
  • cacheStatus: Whether or not the object was found in cache. H for hit, M for miss. "Hit" in this simplified classification includes all responses where a request was not forwarded to origin.
  • serverIdentity: The value of server.identity.
  • remainingTTL: The amount of time in seconds for which the object will remain fresh in the cache (see obj.ttl).
  • staleIfErrorTTL: The amount of time in seconds for which the object will be served stale if no backends are available (see staleness and revalidation).
  • age: The number of seconds for which the object has been in cache.

WARNING: remainingTTL and staleIfErrorTTL are only available when the server handling the request has the object in its own local cache. Otherwise those values will be shown as -. This is typically the case when a cache hit results from clustering, where the request has been forwarded from the server that initially handled it, to the one that has the item in cache. As a result it may be necessary to fetch the URL you are testing repeatedly until you see those values populated.