bit-by-bit vs step-by-step

bit-by-bit and step-by-step both are adjectives.

Word	Noun	Adjective	Verb	Adverb
bit-by-bit	No	Yes	No	No
step-by-step	No	Yes	No	No

As adjectives, bit-by-bit and step-by-step are synonyms defined as:

Other synonyms of bit-by-bit include in small stages, piecemeal, stepwise.

bit-by-bit (adjective)	step-by-step (adjective)
one thing at a time	one thing at a time