SpellCheckerBot

For Russian text the practical question is not grammar theory but the two mistakes that actually embarrass you: a misspelt word and the same word three times in a paragraph. The bot covers both — spelling through the Yandex speller engine, which handles Russian morphology properly, and a check for repetitions.

That makes it a reasonable last pass before sending something: a post, a listing, a message to a client. It is not an editor and will not rewrite a clumsy sentence; it tells you where the text is wrong, and the wording stays your problem.