ETags, or entity-tags, are an important part of HTTP, being a critical part of caching, and also used in "conditional" requests. So what is an etag?

Part of the problem may be that my sparklines web service returns an ETag with each response.

Part of the problem may be that my sparklines web service returns an ETag with each response.

Entity tags are used for comparing two or more entities from the same requested resource.

The ETag response-header field provides the current value of the entity tag for the requested variant.

A client that has one or more entities previously obtained from the resource can verify that one of those entities is current by including a list of their associated entity tags in the If-Match header field.

A client that has one or more entities previously obtained from the resource can verify that none of those entities is current by including a list of their associated entity tags in the If-None-Match header field.

HTTP is typically used for distributed information systems, where performance can be improved by the use of response caches. The HTTP/1.1 protocol includes a number of elements intended to make caching work as well as possible. Because these elements are

Sure, the server response may contain an ETag header, you save this away ascociated with the URL, then on subsequent requests for that url, you include a If-None-Match header with the etag value. If the contents haven't changed, then the server will reply