In fact, Yagnobi is just the continuation of one of Sogdian dialects. It has 8 vowels - 5 long and 3 short; and 27 consonant sounds. The morphology is distinguished by combination of inflected and analytic forms - both in verbs and in nominal parts of speech. Many grammar models were borrowed from Tadjik parallel forms. The vocabulary is full of Tadjik borrowings, and the original Sogdian lexics can be met mostly in verbs and pronouns.
Yagnobi is used also among Tadjiks as a "secret", "taboo" language, and the roots for this tradition go far in the history.