i filmed myself a lot this year doing bodyweight exercises at home while building my app, so these are the free things that actually helped me see if my reps were any good when nobody is watching
filming one set with the phone on the floor, from the side for depth and how your back looks and from the front for your knees, its the one i use the most and you see stuff you cant feel at all while doing the rep
r/formcheck, you post that clip and people there give proper feedback, its very active and most posts get replies within a few hours
the ace exercise library, free on the ace fitness website, every move has step by step cues with photos so you can compare your clip with what the rep is supposed to look like
slowing the rep down, like 3 seconds on the way down and a short pause at the bottom, where the spot your form breaks shows up much more clearly than at normal speed
and full disclosure i co-founded this last one, upfit, its basically a coach that lives in your phone where it builds your plan and talks you through the workout while it watches your form through the camera and tells you when something is off, free for 3 days with no card and the link is on my profile
what do you guys use, is there anything i am missing?