on your resume, did you put how good/experienced you are at each skill?

I did but I limited it to a scale of "very familiar with, know, have used".

nope

Never.

Well I mention overall not with each skill

I did group my skills into 3 categories:
-- confident
-- good enough
-- getting rusty

some tools I haven't used for a while and I'm getting rusty. Remembering them will be easier than learning anew.

Others I use as my BAU and feel confident about them.

The rest I use occasionally - I know how to get things done but I'm prolly not the right person if you want to train someone else to use it.

Resumes are primarily meant to be fed into a machine. Check the boxes the job asks for, list relevant experience and not much else.

The entire process is a balancing act between giving enough info to get through the filters, and not so much that you may be filtered by someone's bias.

You can always qualify your skill level during the interview. Pre-qualification only works against you.

Idk about resumes but I almost always ask interviewees how well they know the stuff they put on there anyway. Seems like a useful thing to add but probably depends on country and culture.

I see some cvs posted here and I don't get what are the metrics behind the dots (3 out of 5) or percentages that someone uses next to a skill (or more specifically a programming language)

Never ever helped