A hiánypótlás kötelező.

In Hungarian, the verb to be is often left out in the present tense, third person.

So:

• A hiánypótlás kötelező. = The hiánypótlás is mandatory.

If you said it in the past or future, or with I/you/we, the verb would appear:

• A hiánypótlás kötelező volt. = It was mandatory.
• A hiánypótlás kötelező lesz. = It will be mandatory.
• Kötelező vagyok would be ungrammatical here, but in other sentences with different subjects, the verb would be used.

This missing-is pattern is one of the first things English speakers notice in Hungarian.

A is the definite article, meaning the.

Hungarian has two forms of the definite article:

• a before consonant sounds
• az before vowel sounds

Since hiánypótlás begins with h, which counts as a consonant sound, the sentence uses:

• a hiánypótlás

So this is literally the hiánypótlás.

Hiánypótlás is a noun.

It is built from:

• hiány = lack, deficiency, missing item
• pótlás = replacement, supplying, making up for something

Together, hiánypótlás is a set expression, especially common in official or administrative language, for something like:

• supplying missing documents/information
• correcting an incomplete submission
• deficiency correction

So grammatically, in this sentence, a hiánypótlás is the subject.

Hungarian often forms compound nouns by writing them as one word.

Here:

• hiány
  • pótlás → hiánypótlás

This is very normal in Hungarian. English often prefers separate words, but Hungarian frequently combines them into compounds.

So even if an English speaker expects something more like missing-document submission or deficiency correction, Hungarian naturally uses one compound noun here.

Yes, kötelező is an adjective meaning mandatory, obligatory, or required.

In this sentence, it works as a predicate adjective:

• A hiánypótlás kötelező.
• literally: The hiánypótlás mandatory.
• natural English: The hiánypótlás is mandatory.

Hungarian does this very often: a noun + adjective, with the present-tense is omitted.

Because Hungarian adjectives generally do not agree with the noun in the way they do in many Indo-European languages.

So you do not need different forms for masculine/feminine/neuter or singular/plural here.

• A hiánypótlás kötelező.
• A dokumentumok kötelezőek / kötelezők. = The documents are mandatory.

In predicative use, Hungarian adjectives stay much simpler than English speakers might expect if they know languages with adjective agreement.

Also, in your sentence the subject is singular, so plain kötelező is exactly what you want.

This is a very neutral, standard word order:

• A hiánypótlás kötelező.

It presents the subject first and then says something about it.

You can change Hungarian word order for emphasis, but that changes the focus:

• Kötelező a hiánypótlás.
  = It is the mandatory nature of it that is emphasized a bit more, or it can sound more like an announcement.

Both are possible, but A hiánypótlás kötelező is the straightforward default sentence.

A rough pronunciation is:

• hee-aany-poht-laash

A few helpful points:

• á is a long vowel, somewhat like a in father, but longer
• ó is also long
• s in Hungarian sounds like English sh
• so the end -lás sounds roughly like laash

Also, Hungarian stress is always on the first syllable:

• HIÁNYPÓTLÁS

That fixed first-syllable stress is very important in Hungarian pronunciation.

Yes, very much. In Hungarian, accent marks are not optional decoration; they are part of the spelling and pronunciation.

For example:

• a and á are different vowels
• o, ó, ö, and ő are all different vowels

So in:

• hiánypótlás
• kötelező

the accented vowels must be written correctly. They affect both pronunciation and sometimes meaning.

Yes, it sounds fairly formal or administrative, mainly because of the word hiánypótlás.

You are especially likely to see it in:

• government paperwork
• university administration
• application procedures
• legal or official notices

The grammar itself is completely normal, but the vocabulary gives it a more official tone.