You also need to match the connectors to the cable (stranded v. solid), cat 5 connectors don't work well with cat 6 cable, it's basically impossible to get good strain relief with self-terminated RJ45 (the slip on plastic boots are too big when used with a high density switch) etc.
It was with the >$500 crimp tool I used to use at work.
Not so much with a crimp tool that's part of a £15 networking equipment kit bought off ebay.
I don't do enough of it to warrant spending any more on them.