Rules for writers, Tenth edition - Diana Hacker, Nancy Sommers 2021

Use adverbs to modify verbs, adjectives, and other adverbs
Choose adjectives and adverbs with care
Grammar

When adverbs modify verbs (or verbals), they nearly always answer the question When? Where? How? Why? Under what conditions? How often? or To what degree? When adverbs modify adjectives or other adverbs, they usually qualify or intensify the meaning of the word they modify. (See 47e.)

Adjectives are often used incorrectly in place of adverbs in casual or nonstandard speech.