What does "ei" mean in the Google homepage url https://www.google.co.in/?gws_rd=cr&ei=xgH...?

Question

I know about some of the parameters in a google url, such as:

• gws =google web server
• rd = redirected
• cr = country reffered

But I noticed one I cannot identify: &ei=. What does the ei mean in this URL?

http://www.google.co.in/url?ei=qWwlUqD4MIrRrQfD9ICIDw&...etc... 

Answer 1

The ei parameter contains a timestamp—probably with microseconds—which corresponds to the time when the search results were served.

Your particular ei value (qWwlUqD4MIrRrQfD9ICIDw) contains the following values:

Array (     [0] => 1378184361     [1] => 801824     [2] => 15427722     [3] => 4043323971 ) 

The timestamp (1378184361) corresponds to 03/09/2013 05.59.21. The microseconds are 801824 (probably).

(Unfortunately no-one is going to be able to confirm whether they are microseconds or not, but the timestamp (in seconds) is obvious.)

See this guide to decoding ei values, which also provides an open-source PHP function.