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.