Can an app check my lifting form?
Yes — within honest limits. Phone pose tracking can now reliably measure the objective parts of form: range of motion (squat depth), movement speed (tempo), and rep completion, live and on-device. What it can't do is feel what a great coach feels — breathing, bracing, intent. The right way to use a form app is for the measurable fundamentals, every single rep, at a price and availability no human can match.
What's genuinely measurable
Joint angles (is the hip below the knee?), rep tempo (was the descent controlled or a bounce?), rep counting, and consistency across a set. These are geometry and time — exactly what computer vision is good at, and exactly the faults that quietly erode most lifters' training.
What still belongs to a human coach
Bracing and breathing quality, pain versus discomfort, bar-path subtleties on maximal attempts, and the last-2% technique work of competitive lifters. An app that claims otherwise is overselling. Spotter's scoring is deliberately scoped to depth and tempo — the two signals it can measure well every rep.
Live beats after-the-fact
Most form apps grade an uploaded clip: useful audit, weak habit. Live scoring changes behaviour because the feedback arrives while you're still at the bar — the rep count spoken out loud, a warning tone on a shallow rep, the coaching note before your next set. That's the cadence of a coach, not a report.
Privacy is part of the answer
Form checking means filming yourself training. Spotter's analysis runs entirely on-device with Apple's Vision framework: no video upload, no cloud storage, nothing identifiable leaving the phone — only numeric rep scores, which also power the coaching notes and weight progression.
Answers
How accurate is phone-based form analysis?
For measurable fundamentals — depth, tempo, rep counting — modern on-device pose tracking is accurate enough to score every rep in real time. For subtle technique judgment, a human coach still wins.
Do I need special equipment?
No. A phone propped side-on about 3 metres away, full body in frame. Spotter tracks joint angles from the standard camera — no wearable, no depth sensor, no second device.
What does Spotter do when a rep is bad?
It scores it lower, plays a warning haptic/tone, and factors it into the set report. If depth wasn't there across the set, the weight holds next session instead of progressing — the score has consequences, like a real coach's eye.
Related: Is my squat deep enough? · AI squat form app · How Spotter works