Missing comma before clause

One of 72 rules YabLab tracks in Russian writing.

A typical slip

Я точно знаю что ты прав.

Я точно знаю, что ты прав.

The rule

Missing comma before clause

Punctuation marks the boundaries and relationships that speech expresses through pauses and intonation. Each mark must match the sentence structure.

Structure first
Identify clauses and phrases A comma, period or other mark follows the grammatical boundary, not the length of the sentence.
Meaning
Choose the relationship Different marks can signal continuation, separation, explanation or interruption.
Read aloud
Use sound only as a final check A pause can confirm a boundary, but grammar decides whether punctuation is required.

What YabLab does with this mistake

  1. Catches it right as you write — comments, email, docs.
  2. Explains the why in your language, not just the fix.
  3. Helps you practice it until it is gone for good.