Tests, lessons that build up the keyboard, and code with no autocomplete.
Click the box and start typing; the clock starts on your first key. Backspace works.
WPM counts the correct characters left on screen, five to a word, divided by minutes. Raw WPM counts every key you pressed, right or wrong. Accuracy is correct keystrokes over all keystrokes, so a mistake you backspace over still counts: you made it.