For derusting tools, there is a commonly used method (in the woodworking and antiques trades) of doing it without removing any good metal at all - which is not true of any of the acid methods as far as I know. Do a google search on Reverse Electrolysis and you will find many simple descriptions, as well as a few that get too fussy and complicated.

It is not practical for frames, and will lift chrome or paint if they have the least bit of rust under them. So it is good but for simple steel items... like tools.