Не испорти сюрприз.

Испорти is the imperative form of the verb испортить, which means to spoil, to ruin, or to mess up.

So Не испорти сюрприз literally means:

• Don’t spoil the surprise
• Don’t ruin the surprise

In natural English, spoil the surprise is often the most idiomatic translation.

Because испортить is the infinitive: to spoil / to ruin.

In the sentence, Russian needs a command form: don’t spoil...

So the verb changes from the infinitive to the imperative:

• испортить = to spoil
• испорти = spoil! / don’t spoil!

With не, it becomes a negative command:

• Не испорти = Don’t spoil

It comes from испортить.

The singular imperative here is:

• испортить → испорти

This is the form used when speaking to one person in an informal ты situation.

Related forms:

• испорти — informal singular: don’t spoil
• испортите — plural or polite: don’t spoil

So if you were speaking politely or to more than one person, you would say:

• Не испортите сюрприз.

Не is the standard Russian word for not.

With an imperative, it makes a negative command:

• Испорти сюрприз. = Spoil the surprise.
• Не испорти сюрприз. = Don’t spoil the surprise.

So the structure is very straightforward:

• не + imperative verb

This is one of the most important questions in Russian.

• испортить is perfective
• портить is imperfective

Both can appear in negative commands, but the nuance changes.

Не испорти сюрприз

This means something like:

• Don’t end up spoiling the surprise
• Make sure you don’t ruin it
• a warning about one specific result

It focuses on the completed bad outcome.

Не порти сюрприз

This sounds more like:

• Don’t spoil the surprise
• Don’t be ruining it
• Stop spoiling it / don’t do that kind of thing

It can sound more like a general prohibition, repeated behavior, or an ongoing action.

In this sentence, Не испорти сюрприз is very natural if someone is warning another person not to give something away.

It is in the accusative case, because it is the direct object of the verb:

• spoil what? → the surprise

So grammatically:

• испортить что? → сюрприз

However, for masculine inanimate nouns, the accusative often looks exactly like the nominative.

That is why you see:

• nominative: сюрприз
• accusative: сюрприз

Same form, different function.

Because сюрприз is:

• masculine
• inanimate
• singular

For masculine inanimate nouns in Russian, the accusative singular is usually the same as the nominative singular.

So:

• Это сюрприз. = This is a surprise.
  Here сюрприз is nominative.
• Не испорти сюрприз. = Don’t spoil the surprise.
  Here сюрприз is accusative.

Same form, different grammatical role.

In Russian, the subject you is usually not stated in commands, because it is understood from the imperative form.

So Не испорти сюрприз means:

• You, don’t spoil the surprise

But Russian normally leaves out the pronoun unless it is being emphasized.

Because the verb is испорти, we know it is addressed to:

• one person
• in an informal way (ты)

If you wanted the polite/plural version, you would use:

• Не испортите сюрприз.

It is informal singular.

That is because испорти is the imperative used with ты.

So you would say this to:

• a friend
• a child
• a family member
• someone you address as ты

For polite or plural you, use:

• Не испортите сюрприз.

So the contrast is:

• Не испорти сюрприз. — one person, informal
• Не испортите сюрприз. — polite singular or plural

The stress is:

• Не испор́ти сюрпри́з.

More clearly:

• испор́ти — stress on -рó-
• сюрпри́з — stress on the last syllable

A rough pronunciation guide:

• nee ees-par-TEE syur-PREES

That is only approximate, but it helps as a starting point.

The normal order here is:

• Не испорти сюрприз.

This is the most natural neutral order:
not + verb + object

Russian word order is flexible, but changing it usually changes the emphasis.

For example:

• Сюрприз не испорти. — possible, but marked; it sounds like special emphasis on the surprise
• Не сюрприз испорти... — not natural for this meaning

So in ordinary speech, stick with:

• Не испорти сюрприз.

By itself, it is usually neutral to mildly firm.

The tone depends a lot on context and intonation.

It can sound like:

• a simple warning
• a friendly reminder
• a firm request

For example, said warmly, it could mean:

• Don’t spoil it!

Said sharply, it could sound more like:

• Don’t you dare ruin the surprise.

So the grammar itself is not rude; the tone comes from the situation and voice.

Yes — and in many contexts, Don’t spoil the surprise is actually the most natural English translation.

Russian испортить has a broad meaning: to spoil, to ruin, to mess up.

With сюрприз, English often prefers spoil the surprise, especially if the idea is:

• don’t reveal it too early
• don’t give it away
• don’t ruin the effect

So depending on context, all of these can work:

• Don’t spoil the surprise
• Don’t ruin the surprise
• Don’t give the surprise away (more interpretive, but often very natural)

Yes, you could, but it is not exactly the same.

Не испорти сюрприз

• focuses on a single result
• sounds like a warning: make sure this does not happen

Не порть сюрприз

• imperfective
• sounds more like don’t be spoiling it, don’t spoil it in general, or stop doing that

If someone is about to reveal a secret, Не испорти сюрприз is very natural.

If someone keeps making comments that are ruining the mood, Не порти сюрприз may sound more appropriate.

So both are possible, but the aspect changes the nuance.