Good GDZ sources provide explanations for why a comma is used or how a word is decomposed.
Known for providing multiple ways to solve a single exercise.
If you want to find a specific exercise or need a breakdown of a particular grammar rule: (e.g., Exercise 142) The Topic (e.g., Participles, Verbs, or Nouns)
Most sites allow you to type the exercise number directly.
Remember that the 6th-grade textbook is often split into Part 1 and Part 2.
(e.g., the 2023 "Prosveshcheniye" version)