Learn Hardcore German: Am Schluss der Feier sind alle satt und müde, aber glücklich. - At the end of the celebration everyone is full and tired, but happy.

Am Schluss = at the end (of something), often a process or event
- Am Schluss der Feier = at the end of the party
Am Ende = also “at the end”, slightly more neutral and very common
- Am Ende des Films = at the end of the film
Zum Schluss = “finally / in conclusion / at the end (as the last point)”
- Zum Schluss sagte er Danke. = Finally / In conclusion he said thank you.

In your sentence, Am Schluss der Feier could also be Am Ende der Feier without changing the meaning. Zum Schluss would sound more like “Finally, at the party, everyone is full and tired, but happy,” which slightly shifts the focus to the last action rather than simply the time point.

Why is Schluss capitalized, and what is am grammatically?

Schluss is capitalized because it is a noun. In German, all nouns are capitalized.

am is a contraction of an dem:

an = preposition that can take dative or accusative
dem = dative masculine/neuter article (“the”)

So:

an dem Schluss → am Schluss

Here Schluss is masculine, so in the dative it’s dem Schluss, contracted to am Schluss.

Why is it der Feier and not die Feier or von der Feier?

Die Feier is the basic (nominative) form:

Nominative: die Feier (the party/celebration)

In am Schluss der Feier, der Feier is genitive singular, depending on Schluss:

der Schluss der Feier = the end of the party

So the structure is:

am Schluss (dative)
- der Feier (genitive)
  = at the end of the party

You could also say:

am Ende der Feier (same structure)
am Schluss von der Feier is possible in everyday speech, but sounds less elegant or more colloquial. The genitive (der Feier) is the standard written form.

What does Feier mean exactly, and how is it different from Party or Fest?

Feier is a general word for a celebration or festive event. It can be formal or informal:

Geburtstagsfeier = birthday celebration
Weihnachtsfeier = Christmas party (often work-related)
Hochzeitsfeier = wedding reception/celebration

Compared:

Party = usually an informal, often younger, more “English-influenced” word; think of a house party, club party, etc.
Fest = “festival / (public) festivity,” often larger or more traditional
- Volksfest, Oktoberfest, Straßenfest

In your sentence, Feier suggests a celebration (e.g. birthday, wedding, office party) rather than a big public festival.

Why does the verb sind come before alle? I thought German word order was like English: Subject–Verb–Object.

German main clauses follow the “verb-second” rule (V2), not strict SVO.

The finite verb must be in second position in the sentence, but “second position” means second element, not the second word.

Your sentence:

Am Schluss der Feier = first element (a time phrase)
sind = finite verb (must be in second position)
alle satt und müde, aber glücklich = the rest (subject + predicates)

So the underlying order is still:

Alle sind satt und müde, aber glücklich. (Subject–Verb–Complement)

When you move Am Schluss der Feier to the front for emphasis or style, the verb jumps before the subject to remain in second position:

Am Schluss der Feier sind alle satt und müde, aber glücklich.

What does alle refer to here? Does it need a noun after it?

Here alle is a pronoun meaning “everyone / all (of them)”.

Alle sind satt und müde… = Everyone is full and tired…

In other contexts, alle can also be a determiner before a noun:

Alle Gäste sind satt und müde. = All (the) guests are full and tired.

In your sentence, the people have already been mentioned or are obvious from context, so German can just say alle (“everyone”) without repeating the noun.

Why is it sind and not ist?

Sind is the 3rd person plural form of sein (“to be”).
Ist is the 3rd person singular form.

The subject is alle (“everyone / all”), which is grammatically plural, even though in English you might say “everyone is”.

So German requires the plural verb:

Alle sind … (not Alle ist…)

Why don’t the adjectives satt, müde, and glücklich have endings like satte or müden?

Because here they are predicate adjectives after the verb sein:

alle sind satt
alle sind müde
alle sind glücklich

Predicate adjectives in German never take endings.

Adjective endings appear only when the adjective stands directly in front of a noun (attributive position):

die müden Gäste = the tired guests
die glücklichen Kinder = the happy children
ein satter Hund = a full/satisfied dog

But after sein, werden, bleiben (and similar verbs), the adjective is uninflected:

Die Gäste sind müde.
Die Kinder bleiben glücklich.

What is the difference between satt and voll when talking about eating?

In English you say “I am full” after eating.
In German you normally say Ich bin satt.

satt = full (because you have eaten enough), satisfied in terms of food
- Ich bin satt. = I’m full / I’ve had enough to eat.
voll = full (physically filled up), or colloquially drunk
- Das Glas ist voll. = The glass is full.
- Ich bin voll. (colloquial) = I’m drunk.

So in the sentence:

alle sind satt und müde = everyone has eaten enough and is tired.

Saying alle sind voll would sound like “everyone is drunk” (and is not what you want here).

Why is there a comma before aber?

Aber is a coordinating conjunction meaning “but”. In German, a comma is required before most coordinating conjunctions when they connect independent clauses or larger parts of a sentence:

…, aber …

In your sentence:

[Am Schluss der Feier sind alle satt und müde], aber [glücklich].

The second part is a shortened clause (elliptical); the full form would be:

Am Schluss der Feier sind alle satt und müde, aber (sie sind) glücklich.

Even with this ellipsis, the comma before aber stays.