Same word as painstaking:

assiduous, by the book, by the numbers, careful, conscientious, conscionable, diligent, earnest, exact, exacting, finicky, fussbudget, fussy, hard-working, heedful, industrious, particular, persevering, persnickety, picky, punctilious, punctual, scrupulous, sedulous, stickler, strenuous, thoroughgoing