Adjective Endings
Adjective agreement
Swedish adjectives change their ending to match the noun they describe.
En words
With an en noun, the adjective uses its basic form:en stor bil(a big car)
Ett words
With an ett noun, the adjective usually adds -t:ett stort hus(a big house)
Plural and definite form
With plural nouns and the definite form, the adjective adds -a:stora bilar(big cars)
stora hus(big houses)
den stora bilen(the big car)
det stora huset(the big house)
This is called adjective agreement. The adjective agrees with the noun in gender and number.
Where most adjectives have three forms, there are exceptions to this rule. For instance liten has four forms partly based on different stems: liten (en word), litet (ett word), lilla (definite singular), and små (plural). Normally the definite and plural share one -a form built from the basic stem. So since liten ends in -en, it is expected to change analogous to e.g. öppen → öppna. However, since liten is irregular, the hypothetical litna just does not exist.
Some adjectives are defective, meaning they lack certain forms — most often the neuter or -t form, like rädd.
A handful of adjectives are easy to use because they never change. This includes among others bra, kul, and gratis and colors like rosa, beige, and lila.
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The full grammar article explains how Swedish adjective endings work with en nouns, ett nouns, and plural nouns, including adjective agreement after verbs, adverbial -t, spelling changes, indeclinable adjectives, and common mistakes.