Does this exist? Or it is again just the "suggested size" with no hard limits? Im trying to figure out how to best store them in a database.
Tags on the sites are, at most, 25 characters.
Permitted characters are
a-z 0-9 + # - .
However, this is not part of the API contract insofar as if the site definition of a tag changes so will the API's. It is advisable, for correctness, to have a code path to handle tags > 25 characters in length. Simplest would be to truncate them.
All that being said, there are no plans to change tag lengths at this time.