Atbash of tsryb → ghiby (not English). Caesar ROT-5: tsryb → yxwdg (nonsense).
So not ROT-13.
Given the lack of context, the most useful review I can give is: tsryb fydyw nwdz ktkwtt msryt shrynyt... REPACK
A quick check shows that if you apply a (or +21 in the other direction), it may decode to something readable. Atbash of tsryb → ghiby (not English)