Im Text wird die Ursache des Fehlers beschrieben.

Im is a contraction of in dem.

• in dem Text = im Text

German very often contracts certain preposition + article combinations in everyday usage, and im is the normal form here.

So:

• im Text = in the text

Both are possible grammatically, but im Text sounds more natural in most contexts.

This is because the sentence is in the present passive.

German passive is often formed with:

• werden
  • past participle

Here:

• wird = present tense of werden
• beschrieben = past participle of beschreiben

So the full passive verb is:

• wird beschrieben = is described

In a main clause, the finite verb (wird) goes in the second position, and the past participle (beschrieben) goes to the end.

That is why the sentence looks like this:

• Im Text wird die Ursache des Fehlers beschrieben.

Yes, it is a passive sentence.

A good sign is the pattern:

• werden
  • past participle

Here that pattern is:

• wird beschrieben

The passive focuses on what is being done, not on who does it.

So instead of saying:

• Someone describes the cause of the error in the text

German says:

• In the text, the cause of the error is described

This is very common in formal, academic, and technical German.

A natural active version would be:

• Im Text beschreibt man die Ursache des Fehlers.

Literally:

• In the text, one describes the cause of the error

Or with a more explicit subject, depending on context:

• Der Text beschreibt die Ursache des Fehlers.

The passive version avoids naming the agent and sounds more formal or impersonal.

Ursache is a feminine noun:

• die Ursache = the cause

In this sentence, it is also the grammatical subject of the passive sentence, so it stays in the nominative case.

Compare:

• active: Man beschreibt die Ursache des Fehlers.
  Here die Ursache is the direct object.
• passive: Die Ursache des Fehlers wird beschrieben.
  Here die Ursache becomes the subject.

So die is used because:

1. Ursache is feminine
2. it is nominative singular here

Because des Fehlers is genitive.

The phrase die Ursache des Fehlers means:

• the cause of the error

In German, relationships like of the error are often expressed with the genitive case.

So:

• der Fehler = the error (nominative)
• den Fehler = the error (accusative)
• des Fehlers = of the error (genitive)

The -s on Fehlers is a normal genitive ending for many masculine and neuter singular nouns.

German main clauses follow the verb-second rule.

That means the finite verb must come in the second position, but the first position can be taken by different elements.

Here, Im Text is placed first for emphasis or topic:

1. Im Text
2. wird
3. die Ursache des Fehlers
4. beschrieben

So the sentence structure is perfectly normal.

You could also say:

• Die Ursache des Fehlers wird im Text beschrieben.

That version starts with the subject instead.

Yes, absolutely.

Both are correct:

• Im Text wird die Ursache des Fehlers beschrieben.
• Die Ursache des Fehlers wird im Text beschrieben.

The difference is mainly focus:

• Im Text ... puts emphasis on where it is described
• Die Ursache des Fehlers ... puts emphasis on what is described

German word order is flexible in this way, as long as the finite verb stays in second position in a main clause.

The infinitive is:

• beschreiben = to describe

The past participle is:

• beschrieben = described

This is a strong verb, so its forms include a vowel change:

• beschreiben
• beschrieb
• beschrieben

In the sentence, beschrieben is used as part of the passive construction:

• wird beschrieben

Because passive sentences often leave out the agent when it is:

• unknown
• unimportant
• obvious from context
• deliberately not emphasized

In technical or academic writing, German often prefers this style.

If you wanted to include the agent, you could say something like:

• Im Text wird die Ursache des Fehlers vom Autor beschrieben.

That means:

• In the text, the cause of the error is described by the author.

But very often, German simply leaves that part out.

Yes, very common.

The passive is especially frequent in:

• academic writing
• technical documentation
• reports
• formal explanations

That is because it sounds objective and impersonal.

So a sentence like:

• Im Text wird die Ursache des Fehlers beschrieben.

sounds very natural in formal written German. In everyday spoken German, people might more often use an active sentence instead.