ETag
HTTP header that identifies a specific version of a resource; enables conditional requests and 304 Not Modified to save bandwidth.
Definition
An ETag (entity tag) is an opaque string returned in the ETag response header that identifies the current version of a resource (e.g. a hash of the content). On a subsequent request, the client can send If-None-Match: "that-etag"; if the resource is unchanged, the server responds with 304 Not Modified and no body. This reduces bandwidth and lets crawlers check for updates without re-downloading full pages.
Relevance to GEO
ETags help AI crawlers and CDNs avoid re-fetching unchanged content, reducing load and speeding up freshness checks. Use with Cache-Control for an effective caching and revalidation strategy.