Антиплагиат уже проверил текст.

Антиплагиат is usually the name of an anti-plagiarism system or website, something like Antiplagiarism or the plagiarism checker.

It is capitalized because it is being used like a name. In Russian, names of services, programs, and platforms are often treated this way.

Grammatically, it behaves like a masculine singular noun, which is why the verb form is проверил.

Проверил is past tense: checked or has checked.

So the sentence means that the checking is already completed.

Compare:

• проверяет = is checking / checks
• проверил = checked / has checked
• проверит = will check

In this sentence, проверил shows a finished action in the past.

In Russian, past tense is often formed with -л plus endings that show gender and number.

Here are the singular forms:

• проверил = masculine
• проверила = feminine
• проверило = neuter

And plural:

• проверили = plural

Since Антиплагиат is treated as a masculine singular noun, the verb is проверил.

This is about aspect, which is very important in Russian.

• проверил is perfective
• проверял is imperfective

Проверил focuses on the completed result: the text has already been checked.

Проверял would suggest the process or repeated action, for example:

• Антиплагиат проверял текст = The anti-plagiarism system was checking the text / used to check the text.

Because the sentence contains уже and clearly refers to a completed result, проверил is the natural choice.

Текст is the direct object, so it is in the accusative case.

But for many inanimate masculine nouns in Russian, the accusative singular looks exactly like the nominative singular.

So:

• nominative: текст
• accusative: текст

That is why the object form does not visibly change here.

Уже usually means already.

In this sentence, it adds the idea that the action has been completed by now or sooner than expected / at this point:

• Антиплагиат уже проверил текст = The anti-plagiarism system has already checked the text.

Without уже, the sentence would simply mean:

• Антиплагиат проверил текст = The anti-plagiarism system checked the text.

So уже adds the sense of already.

That word order is very natural in Russian.

• Антиплагиат уже проверил текст.

Here, уже modifies the whole action: already checked.

Russian word order is more flexible than English, so other orders are possible, but they may sound more marked or put emphasis in a different place.

For example:

• Антиплагиат уже проверил текст. = neutral, natural
• Текст уже проверил Антиплагиат. = stronger emphasis on the text
• Антиплагиат проверил текст уже. = possible in speech, but less neutral

So the original order is the best basic version to learn.

Russian has no articles, so there is no word corresponding directly to a or the.

Whether текст means a text or the text depends on context.

So:

• Антиплагиат уже проверил текст could mean
  The anti-plagiarism system has already checked the text

  or, depending on context,

  ...has already checked a text

In most situations, context makes it clear.

Yes, grammatically it can act as the subject just like a person or any other noun:

• Антиплагиат проверил текст.

Even though it is a system or service, Russian often uses such nouns directly as subjects with normal verb agreement.

English does something similar:

• Google found the file
• The software checked the document

So this structure is completely normal.

A helpful stress pattern is:

Антиплагиа́т уже́ прове́рил текст.

Roughly: Antiplagiát uzhé provéril tekst

Important stresses:

• антиплагиа́т
• уже́
• прове́рил
• текст

The word текст is one syllable, so it is naturally stressed there.

Yes. In many contexts, has checked is the best English translation.

Russian does not have a separate grammatical form exactly matching the English present perfect, so the past tense проверил can correspond to either:

• checked
• has checked

In this sentence, because of уже, English often prefers:

The anti-plagiarism system has already checked the text.

That usually captures the meaning best.