Agree, I didn't understand that one can change the WPM before reading this thread.

Good point, I've added a help button in the top left corner that briefly explains the concept. Maybe that already helps a bit.

it helps, but I was very confused at first too (the button is not very visible)

Do you have any ideas for the feedback when your speed is to low? I am not a designer and struggle to find ideas that keep the UI as minimal as it is right now while improving the user experience.

I like the minimal feedback as it is right now: you just have to try again.

A hint at what wpm I just typed at would be nice. So if I only hit 50 wpm a 50 off to the side or below the dotted line.

This is fascinating when picking a liminal wpm. Single hand words are so much harder.

I can cruise along until I hit words like "exact"

EDIT: You could make a list of bigrams as people type and average the wpm for words with that bigram, then you could weight the randomly chosen words by the difficulty of the bigrams, to really help people focus on their biggest stumbling blocks.

the dashed line under the input could be briefly turned red (for 400-500ms) when you clear it on fail

I think just a brief "too slow" underneath the input would suffice.