This document presents our research on the the correct formation of a Classical Tibetan syllable. It was triggered by attempts at defining the boundaries of well-formed syllables in Classical Tibetan for spell checking purposes. Formalizing the formation of the syllable led us to inspect the small differences among grammar books, both in Western and Tibetan language. We then checked these differences against the Tibetan dictionaries we consider reliable, and also against the Kangyur. Our inquiry finally led us to study the way to decompose a syllable, discussing the ambiguous cases, as well as the formation of the Dzongkha syllable.