Adjectives come in 4 patterns. They are called AB, C1, C2, and C3.

AB adjectives decline as follows:
-ys for masculine nouns
-u for feminine nouns
-o for neuter nouns

C2 adjectives decline as follows:
-es for masculine and feminine nouns
-e for neuter nouns

C3 adjectives decline as follows:
-es for feminine nouns
-e for neuter nouns
For masculine nouns, C3 adjectives are only the stem, unless the consonant cluster at the end is hard to pronounce, which is when an E is added to separate the cluster. However, K turns to Č and G to DŽ before an E.

If the adjective doesn’t fall into any of these categories, it is a C1 adjective, which is declined the same for all grammatical genders.