Learn Hardcore Croatian: Lozinka za moj profil je duga, ali sigurna. - The password for my profile is long, but secure.

Lozinka is feminine, singular, nominative.
The adjective dug (long) in feminine singular nominative is duga.
Dugo is the neuter form or an adverb (for a long time), so it wouldn’t agree with lozinka.

So you get:

(ta) lozinka je duga – the password is long
Masculine: (taj) auto je dug – the car is long
Neuter: (to) uže je dugo – the rope is long

Why is it duga, not dugačka? Is there a difference?

Both duga and dugačka can be used and are correct in many contexts, but there is a nuance:

dug/duga/dugo – the basic adjective, long.
dugačak/dugačka/dugačko – often feels a bit stronger or more colloquial, like quite long / rather long.

In this sentence:

Lozinka za moj profil je duga, ali sigurna. – neutral: The password is long, but secure.
Lozinka za moj profil je dugačka, ali sigurna. – can sound slightly more expressive: The password is pretty long, but secure.

Both are fine; duga is simpler and more neutral.

Why do both adjectives end in -a: duga and sigurna?

They both describe the same noun, lozinka:

lozinka – feminine, singular, nominative
Therefore, both adjectives must also be feminine singular nominative.

So:

dug → duga (f. sg. nom.)
siguran → sigurna (f. sg. nom.)

The pattern is:

Masculine: dug, siguran → Lozinka je dug / siguran. ❌ (wrong, gender mismatch)
Feminine: duga, sigurna → Lozinka je duga, ali sigurna. ✅

Can I say ali je sigurna instead of just ali sigurna?

Yes. Both are correct, with a small stylistic difference:

... je duga, ali sigurna. – the verb je is understood from the first part and omitted in the second. This is common and natural.
... je duga, ali je sigurna. – fully repeated verb; also correct, slightly heavier or more emphatic.

In writing, especially in shorter sentences like this, Croatian often omits the repeated verb when it’s clear from context.

Why do we use za in za moj profil? Could it be moj profil alone?

The preposition za here means for:

lozinka za moj profil = password for my profile.

Without za, moj profil would just be another noun phrase next to lozinka, not clearly linked:

lozinka moj profil – ungrammatical.

So you need a preposition (just like in English) to show the relationship:

lozinka za e-mail – password for (the) email
karte za koncert – tickets for the concert

Why is it moj profil and not svoj profil?

Both moj profil and svoj profil can be grammatically correct, but there’s a rule:

svoj is a reflexive possessive: it refers back to the subject of the sentence.

Here, the subject is lozinka (the password), not “I”:

Lozinka za moj profil je duga...
- Subject: lozinka
- Owner of the profile: me (the speaker)
- Since the subject is not the same as the owner, we use moj, not svoj.

You would use svoj when the subject owns the thing:

Ja štitim svoj profil. – I protect my (own) profile.
Subject ja = owner, so svoj.

Why is there a comma before ali?

In Croatian, a comma is used before the conjunction ali (but) when it connects two clauses or predicates:

Lozinka ... je duga, ali sigurna.

This is like English:

The password is long, but secure.

Some parallels:

On je pametan, ali lijen. – He is smart, but lazy.
Idem, ali ne volim to. – I’m going, but I don’t like it.

Can the word order be Moja lozinka za profil je duga, ali sigurna?

Yes, that is possible and grammatical:

Lozinka za moj profil je duga, ali sigurna. – neutral, slightly topic–comment: the topic is the password for my profile.
Moja lozinka za profil je duga, ali sigurna. – puts a bit more emphasis on moja (my), useful if you want to contrast with someone else’s password.

Croatian word order is fairly flexible, but it influences emphasis and what is considered known vs. new information. The original sentence is a very natural neutral variant.

Could I drop je and say Lozinka za moj profil duga, ali sigurna?

In standard Croatian, you cannot drop je here:

Lozinka za moj profil je duga, ali sigurna. ✅
Lozinka za moj profil duga, ali sigurna. ❌ (incorrect in standard language)

The verb biti (to be) is normally required in the present tense:

Ona je liječnica. – She is a doctor.
Kuća je velika. – The house is big.

Only in very colloquial speech or special stylistic contexts (headlines, slogans, poetry) might you see je omitted.

How do I know that lozinka is feminine?

You mostly rely on dictionary knowledge and patterns, but there are helpful hints:

Ending pattern: many feminine nouns end in -a:
- kuća, knjiga, stolica, lozinka.
Adjective agreement: the adjectives duga and sigurna are feminine forms, so they reveal that lozinka is feminine.

Some other examples:

lozinka jaka i sigurna – a strong and secure password (both adjectives feminine)
dobra lozinka – a good password (feminine dobra)

When in doubt, check a dictionary, but -a is often a good clue that the noun is feminine.