Der Eintritt ist heute gratis.

Because Eintritt is a masculine noun in German, so its nominative singular article is der.

• der Eintritt = the admission / the entrance fee / entry
• German nouns have grammatical gender, and you usually need to learn the gender together with the noun.

In this sentence, Eintritt is the subject, so the nominative article der is used.

In this sentence, Eintritt means admission or entry, especially in the sense of the cost of getting in.

So in contexts like museums, concerts, swimming pools, or events:

• Der Eintritt ist gratis. = Admission is free.

Be careful: Eintritt can also mean entry in a more general sense depending on context, but here it clearly refers to admission.

Because German main clauses usually follow the verb-second rule.

In a normal statement, the finite verb goes in position 2:

• Der Eintritt | ist | heute gratis

Here:

1. Der Eintritt = first position
2. ist = second position
3. heute gratis = the rest

This is one of the most important German word-order rules.

Because gratis is being used as a predicate adjective/adverb-like expression after sein.

After verbs like sein, adjectives usually do not take endings:

• Der Eintritt ist gratis.
• Das Essen ist gut.
• Die Preise sind niedrig.

Compare that with an adjective before a noun, where endings are required:

• der kostenlose Eintritt
• ein gratiser Eintritt is not the normal choice; kostenloser Eintritt sounds much more natural

So in this sentence, gratis stays unchanged.

Very close, yes. Both mean free in the sense of costing nothing.

• gratis = free of charge
• kostenlos = free of charge

In many situations, they are interchangeable:

• Der Eintritt ist gratis.
• Der Eintritt ist kostenlos.

A small nuance:

• gratis can sound a bit more like for free
• kostenlos can sound slightly more neutral or formal

Both are very common and correct.

Because German is flexible about word order, but some placements sound more natural than others.

In Der Eintritt ist heute gratis, heute comes before gratis because the sentence is structured like:

• subject: Der Eintritt
• verb: ist
• time expression: heute
• complement: gratis

This is very natural German.

You may also hear:

• Heute ist der Eintritt gratis.

That version emphasizes today more strongly because Heute is in the first position.

Yes, absolutely.

Both are correct:

• Der Eintritt ist heute gratis.
• Heute ist der Eintritt gratis.

The difference is emphasis:

• Der Eintritt ist heute gratis. → neutral statement about the admission
• Heute ist der Eintritt gratis. → stronger focus on today

When you move Heute to the front, the verb still stays in second position:

• Heute | ist | der Eintritt gratis

Because all German nouns are capitalized.

So:

• der Eintritt
• das Haus
• die Musik

This is one of the easiest visual clues in German: if a word is a noun, it is normally capitalized.

Yes. German often uses Eintritt for both the idea of entering and the admission charge, depending on context.

Examples:

• Eintritt nur für Mitglieder. = Entry only for members.
• Der Eintritt kostet 10 Euro. = Admission costs 10 euros.

In Der Eintritt ist heute gratis, it most naturally means admission is free today.

Yes, that is also common.

• gratis
• kostenlos
• umsonst

can all mean free of charge in many contexts.

So these are all possible:

• Der Eintritt ist heute gratis.
• Der Eintritt ist heute kostenlos.
• Der Eintritt ist heute umsonst.

One thing to know: umsonst can also mean for nothing / in vain in other contexts, so sometimes it has a possible double meaning. In this sentence, though, the meaning would normally be clear.

It sounds completely natural.

A native speaker might say it in situations like:

• at a museum
• at a special event
• at a club or concert on a promotion day
• at a public attraction

You could also hear slightly different natural versions such as:

• Heute ist der Eintritt frei.
• Der Eintritt ist heute frei.
• Heute ist der Eintritt kostenlos.

Note that frei is also common for admission is free, especially in everyday speech.