Apparently, by making the bot checker reject most users so that the total number stays small.

The challenge with scaling a url _shortener_ is that multiple urls might end up with the same short url. That presents a scaling challenge where you have to deliberately design a coordination framework across your set of machines, which introduces coordination, a DB, prefixes, and all your favorite answers to the interview question de-jour of the late 2010s.

With a URL _lengthener_ though, you don't need it at all. The sheer amount of possible outcomes means that the odds of ever getting two of the same is infinitesimally tiny.