Why 'super', 'egal' and 'pleite' never take endings
Most German adjectives change their ending before a noun: ein schöner Abend, eine gute Idee. A small group of very common words refuses to do this. Some of them, like super, klasse and prima, can stand before a noun but stay exactly as they are. Others, like egal, pleite and allein, normally cannot stand before a noun at all. They only come after a verb such as sein.
English speakers trip over this in two ways. Once you have drilled adjective endings, you start adding them everywhere, so ein superer Abend slips out. And because English happily says "a broke student" or "an alone man", it feels natural to put pleite or allein in front of a noun. German usually doesn't allow that.
These words split into two groups, and the groups follow different rules:
Words that can go before a noun but never take an ending: super, klasse, prima.
Words that normally go after a verb (sein, werden, bleiben) or describe how something is done: egal, pleite, allein, bereit, gewillt, gratis, online, offline.
Both groups share one result: you never see an ending on them. For group 1 the rule of thumb is to put the word before the noun and change nothing. For group 2 you should keep the word after the verb. If you need it before a noun, use a different word or a relative clause.
Super, klasse and prima all mean "great" and are informal praise. Whatever the gender or case of the noun, they stay unchanged. Only the article shows the grammar.
They work after sein too, of course: Das ist super! Spitze behaves the same way in casual speech.
Egal and pleite describe a state and live after sein. Egal usually comes with a dative person: whoever doesn't care.
Allein follows a verb or describes how someone does something.
Bereit and gewillt usually take an infinitive with zu. Gewillt is more formal and is often negated.
Gratis, online and offline also stay after the verb or work like adverbs.
Schade, schuld (schuld sein), quitt and futsch belong to this group as well: Das ist schade, Wir sind quitt.
The classic mistake is adding an ending out of habit: ein superer Abend or eine prima Idee with an extra -e. Leave the word bare.
For group 2, don't move the word in front of a noun. Use a substitute instead:
- pleite: say eine bankrotte Firma, or eine Firma, die pleite ist.
- gratis: say ein kostenloser Kaffee.
- online, offline: use a compound, as in der Onlinekurs or der Offlinemodus.
- allein: use a relative clause, as in ein Mann, der allein lebt.
- bereit: compounds like einsatzbereit can take endings, but plain bereit stays after the verb.
In very casual speech you may hear things like die pleite Firma. This is colloquial, so don't copy it in careful German.
Never put an ending on these words. Use super, klasse and prima before a noun exactly as they are: ein super Abend. Keep egal, pleite, allein, bereit, gewillt, gratis, online and offline after the verb: Das ist mir egal. When you need one of these meanings before a noun, switch to another word, a compound or a relative clause.