Learn Hardcore Russian: Я проверил текст сообщения и убедился, что всё правильно. - I checked the text of the message and made sure everything was correct.

Russian verbs come in pairs of imperfective (ongoing/habitual) and perfective (completed) aspect.
• проверял (imperfective) would mean “I was checking” or “I used to check.”
• проверил (perfective) means “I checked” – the action is finished.
Since the speaker completed the check, the perfective проверил is appropriate.

Why is текст in the accusative case, and how can I tell?

текст is the direct object of the verb проверил, and in Russian direct objects generally take the accusative case.
• For masculine inanimate nouns like текст, the accusative form looks identical to the nominative, so you don’t see an ending change.
• You know it’s accusative because it answers the question “what did you check?” (что проверил? – текст).

Why is сообщения in the genitive case?

Here сообщения is a genitive attribute modifying текст. In Russian the “of” relationship between two nouns is shown by putting the second noun in the genitive.
• текст сообщения literally means “text of message.”
• If you translated it word-for-word into English you’d say “text of the message,” so Russian marks сообщения as genitive singular.

Why is there a comma before что?

The word что here introduces a subordinate (object) clause: “that everything is correct.” In Russian, subordinate clauses are separated from the main clause by a comma.
Structure:
• Main clause: Я проверил текст сообщения и убедился
• Subordinate clause: что всё правильно

What’s the difference between все and всё, and why do we use правильно instead of правильный here?

• все (plural) means “all” (people or things).
• всё (neuter singular) means “everything.”
In our sentence you assert that “everything” is correct, so you use всё.

As for правильно vs правильный:
• правильно is an adverb meaning “correctly/rightly” and is used to describe a state or action.
• правильный is an adjective meaning “correct” and modifies a noun.
In the clause что всё правильно, you need an adverb to say “everything is correct,” so правильно is the right choice.

What is the difference between убедиться, что and быть уверенным, что?

• убедиться, что is a perfective verb meaning “to make sure (by checking) that…” – it emphasizes the action of verifying.
• быть уверенным, что is an adjective phrase “to be confident/sure that…” – it states a mental state, not the act of checking.
So if you want to say “I actively checked and made sure,” you use убедился, что. If you simply want to say “I am sure that,” you use я уверен, что.

Can you use убедиться в том, что instead of убедиться, что?

Yes. Both are correct:
• убедиться, что всё правильно
• убедиться в том, что всё правильно
Adding в том (literally “in the fact”) is a bit more formal or emphatic, but it doesn’t change the basic meaning.