La sinossi non rivela il finale aperto, dunque evita lo spoiler.

Because sinossi is a singular feminine noun, even though its form may look plural to an English speaker.

A few useful points:

• Sinossi means synopsis.
• It is borrowed from Greek and stays invariable in form, so the singular and plural look the same.
• The article tells you the number:
  • la sinossi = singular
  • le sinossi = plural

So the -i ending here does not mean plural.

In Italian, standard negation is made by putting non directly before the verb.

So:

• rivela = reveals
• non rivela = does not reveal

This is the normal pattern in simple sentences:

• Non capisco = I do not understand
• Non arriva = he/she is not arriving

Rivela is the third-person singular present indicative of rivelare.

That means it matches a singular subject such as la sinossi:

• La sinossi rivela = the synopsis reveals
• La sinossi non rivela = the synopsis does not reveal

The verb rivelare is a regular -are verb.

Italian often leaves out subject pronouns when they are clear from the verb form or the context.

Here, the subject is already stated as la sinossi, so Italian does not need to repeat essa or another pronoun.

This is very common:

• Maria parla = Maria speaks
• Parla bene = she speaks well

In English, you usually need the subject pronoun; in Italian, you often do not.

Finale aperto is a noun + adjective combination:

• finale = ending
• aperto = open

In Italian, adjectives often come after the noun, especially in neutral, descriptive expressions.

So:

• finale aperto = open ending

That is the normal order here. Putting the adjective after the noun sounds natural and straightforward.

Yes. Italian adjectives usually agree with the noun in gender and number.

Here:

• finale is masculine singular
• so the adjective is aperto, also masculine singular

For comparison:

• un finale aperto = an open ending
• una questione aperta = an open question
• finali aperti = open endings

Dunque means something like therefore, so, or then depending on context.

It is correct Italian, but it can sound a bit more formal or literary than quindi or allora in everyday speech.

Very roughly:

• dunque = therefore / so
• quindi = therefore / so
• allora = so / then

In many everyday contexts, learners will hear quindi more often.

Because spoiler begins with sp-, and in Italian masculine singular nouns that begin with:

• s + consonant
• z
• ps
• gn
• and a few other special sounds

usually take lo instead of il.

So:

• lo spoiler
• lo studente
• lo zaino
• lo psicologo

That is why lo spoiler is correct.

Yes. Spoiler is very commonly used in modern Italian, especially in speech, online, and in entertainment contexts.

You may hear things like:

• fare spoiler
• senza spoiler
• attenzione: spoiler
• mi hai fatto uno spoiler

So even though it is an English borrowing, it is well established in Italian usage.

Formally, evita can be either:

• third-person singular present indicative of evitare = he/she/it avoids
• second-person singular imperative = avoid!

So by itself, evita is ambiguous.

In this sentence, the most natural grammatical reading is that it still refers to la sinossi, so:

• la sinossi ... evita lo spoiler

However, a learner may notice that it could also look like a command in another context.

This kind of ambiguity is normal in Italian, and the surrounding context usually makes the intended meaning clear.

Because evitare normally takes a direct object.

So Italian says:

• evitare qualcosa = to avoid something

Examples:

• evitare il problema
• evitare errori
• evitare lo spoiler

You do not need a preposition like di or a before the object in this structure.

It is understandable, but in everyday Italian you might also hear alternatives that sound a bit more idiomatic, especially with spoiler.

For example:

• La sinossi non rivela il finale aperto, quindi non fa spoiler.
• La sinossi non svela il finale, quindi evita gli spoiler.
• La sinossi non anticipa il finale aperto.

A useful note:

• rivelare and svelare are both common for revealing something
• with spoiler, Italians often use expressions like fare spoiler

So the original sentence is workable, but there are several natural variants.