Is into an adverb?

The part of speech of the word into is not an adverb. “Into” typically functions as a preposition (e.g., “I saw her walking into the station just now”).

In some traditional grammars, however, “into” may be classified as a type of adverb when it’s part of a phrasal verb (e.g., “I bumped into her on the way to work the other day”). Modern grammars usually classify “into” as a “particle” in this context.

QuillBot’s free Grammar Checker will instantly tell you if “into” is the correct preposition for your context.