Learn Italian: Il codice è pieno di errori, non possiamo farci niente di buono. - The code is full of errors, we cannot do anything good with it.

Here, ci means "with it" and refers to the code. This is the "instrumental" use of the pronoun ci. Instead of saying non possiamo fare niente di buono con esso (we cannot do anything good with it), Italians use ci to replace con plus the object that was just mentioned.

Could I put ci before the verb instead of attaching it to fare?

Yes! Because fare is paired with the modal verb possiamo, you have two choices for placing the pronoun. You can attach it to the dropped -e of the infinitive (non possiamo farci) or put it before the conjugated verb (non ci possiamo fare). Both are perfectly natural and mean the exact same thing.

Why is there a di in niente di buono?

In English, we just put the adjective right after the word to say "anything good". In Italian, whenever you follow an indefinite pronoun like niente (nothing/anything) or qualcosa (something) with an adjective, you must link them using the preposition di.

Why does the sentence use both non and niente? Doesn't that mean "we cannot do nothing"?