Dnes večer zazvonil zvonek u dveří, ale nikdo tam nebyl.

In Czech, dnes večer is a normal time expression meaning this evening / tonight. Czech often uses bare time words without a preposition in expressions like this.

Compare:

• dnes večer = this evening
• zítra ráno = tomorrow morning
• v noci = at night

So večer here works adverbially, and no preposition is needed.

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

• zazvonil is perfective: it describes a single completed event, like the bell rang.
• zvonil is imperfective: it suggests ongoing or repeated ringing, like the bell was ringing or kept ringing.

In this sentence, the idea is that the doorbell rang once as an event, so zazvonil is the natural choice.

For example:

• Najednou zazvonil zvonek. = Suddenly the bell rang.
• Zvonek dlouho zvonil. = The bell rang for a long time.

In Czech, the past tense is formed differently from English. In the 3rd person, there is usually no separate auxiliary.

So:

• zazvonil = he/it rang
• nebyl = he/it was not

In 1st and 2nd person, you do see auxiliaries:

• zazvonil jsem = I rang / it rang (if speaker is masculine and talking about doing the action)
• zazvonil jsi = you rang

But in the 3rd person, Czech normally just uses the past participle form by itself.

Both are possible. Czech word order is much more flexible than English word order.

Here, Dnes večer zazvonil zvonek... sounds natural because:

• Dnes večer sets the scene first
• then zazvonil presents the event
• then zvonek names what rang

A more neutral version like Dnes večer zvonek zazvonil... is also possible, but the original order flows very naturally in Czech narrative style.

So this is not about strict grammar as much as information structure and emphasis.

u means by, at, near, and in this sentence u dveří means at the door / by the door.

So zvonek u dveří is literally the bell by the door, which in natural English is the doorbell.

Because the preposition u requires the genitive case.

The basic form is:

• dveře = door

But after u, it changes to:

• u dveří = at/by the door

So the form dveří is the genitive form required by the preposition.

Yes. Dveře is a plural-only noun in Czech. Grammatically, it behaves like a plural word even though in English we usually translate it as singular door.

This is similar to how English has nouns like scissors or pants, which are grammatically plural even when they refer to one object.

So:

• dveře jsou otevřené = the door is open
• u dveří = at the door

Even though the English translation is singular, the Czech noun is plural in form.

Yes. It is a perfectly natural descriptive phrase.

• zvonek = bell / buzzer / doorbell
• zvonek u dveří = the bell at the door

In context, a Czech speaker would understand this as a doorbell. Very often, Czech also just says zvonek if the situation is clear.

Yes, it is a kind of double negative by English standards, but in Czech this is normal and required. This is called negative concord.

If you use a negative word like:

• nikdo = nobody
• nic = nothing
• nikdy = never

the verb is also normally negative:

• Nikdo tam nebyl. = Nobody was there.
• Nikdo nepřišel. = Nobody came.
• Nic neřekl. = He/She said nothing.

So nikdo tam nebyl is exactly what Czech grammar expects.

Because nikdo is grammatically singular.

Even though it refers to an unspecified person or people in meaning, Czech treats it as singular for agreement:

• Nikdo tam nebyl. = Nobody was there.

The form nebyl is the default masculine singular past form, which Czech often uses when the gender is unknown or unspecified.

So:

• nikdo ... nebyl = correct
• nikdo ... nebyli = not correct here

Yes, nikdo nebyl would be possible, but tam makes the location clearer.

tam means there, and here it refers back to the place just mentioned — basically there at the door.

So:

• nikdo nebyl = nobody was there / nobody was present
• nikdo tam nebyl = nobody was there, in that specific place

It helps tie the second clause to the door area mentioned in the first clause.

Because a short introductory time expression like Dnes večer normally does not need a comma in Czech.

The comma in the sentence appears before ale, because ale joins two clauses:

• Dnes večer zazvonil zvonek u dveří, ale nikdo tam nebyl.

So the comma is there because of ale, not because of Dnes večer.