1) You are doing browser level cache optimization and bike-shedding, I am looking at it from an ISP level. Once you have a big pipe and many users, things like

1) You are doing browser level cache optimization and bike-shedding, I am looking at it from an ISP level. Once you have a big pipe and many users, things like this actually start to have a noticeable effect on bandwidth usage. Further, no matter what your use case, it has almost no bearing on the normal (statistically normal no digressions please) use case. 2) So I see what you are saying, but you are wrong -- the ETag still requires a lookup of "did content change since then, based on this tag". My system does not preclude a similar mapping of (tag value, last change) in the server. 3) Yeah, I know, my point is that a standardized hashing method for the ETag provides benefits on top of the ETag. Sometimes everyone playing nicely together actually works out better than lots of flexibility.