"Fix your form" is easy advice and a hard thing to act on alone. You can't watch your own squat from the side while you're in it, and a mirror only shows you one angle at a time. That gap — between knowing form matters and actually being able to check it mid-set — is what an entire category of apps has grown up to close. The problem is they close it in very different ways.
Form-correction apps split into two real categories: camera-based checkers like Kemtai, Onyx, and Zing Coach that watch your rep in real time and flag joint angles or depth, and cue-based coaching apps like Krato that pair every prescribed set with the technique cue that keeps it safe and effective. Camera apps catch it as it happens; Krato prevents the miss by telling you what to focus on before the set starts.
What "Correcting Your Form" Actually Requires
Every app in this space is solving one of two different problems, and it's worth being clear on which one you actually have:
- Catching a breakdown you can't see yourself. This is a real-time, in-the-moment problem — your knee caves, your back rounds, and you need something watching that you aren't.
- Not knowing the right form to begin with. This is a knowledge problem. No amount of camera feedback helps if you don't know a squat should track your knee over your toes in the first place — you need the cue before the rep, not a correction after it.
Most people assume they need the first. A lot of bad form is actually the second — nobody ever told them what to check, so there's nothing to watch for even with a camera pointed at them.
Krato
Krato takes the second problem seriously: every exercise in your program comes with an expert coaching cue attached to the set, not filed away in a separate tutorial you have to go find. "3x8 squat" shows up next to the exact thing to focus on — where your knee should track, how deep to go, what a clean rep feels like — so the form guidance is part of the workout, not something bolted on afterward.
Because Krato also adapts your routine session to session based on what you actually logged, the cue you get stays attached to the weight and rep target that's actually appropriate for you that day — not a generic tip disconnected from what you're about to lift.
Every exercise in Krato comes with an expert coaching cue alongside the target, so you know how to hit the number, not just that you have to. Free on the App Store.
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Kemtai
Kemtai uses your phone or laptop camera to track your body in real time during a set, flagging joint angles, tempo, and range of motion as you move. It's built to feel like a trainer standing next to you counting reps and calling out corrections live, which makes it one of the more genuinely real-time options in the category. The trade-off is it needs a clear, well-lit view of your full body, which isn't always practical in a crowded gym.
Onyx
Onyx (Onyx Coach) turns your phone into a motion-tracking coach, using computer vision to count reps and score form on exercises you perform in front of the camera. It leans into feedback as a habit-building loop — you see your form score improve over time, not just a pass/fail on a single set. It works best for bodyweight and dumbbell movements where a single camera angle can capture the full range of motion.
Zing Coach
Zing Coach positions itself as an AI personal trainer that watches your workout through the camera and adjusts in real time, pairing form feedback with rep counting and a generated plan. It's aimed at people who want the camera-based correction and the "what do I do today" program decision handled by the same app, rather than stitching two tools together.
Picking Based on the Problem You Actually Have
- Bad form because nobody's watching? Kemtai, Onyx, and Zing Coach all put a camera on the problem in real time.
- Bad form because you don't know the cue in the first place? That's what Krato is built to prevent — the coaching shows up with the set, before the rep happens.
- Training in a crowded gym without room to set up a camera? Camera-based apps need a clear line of sight; a cue-based approach works anywhere you can read your phone between sets.
Neither category is strictly better — they're catching the problem at a different point. One watches the rep as it happens. The other makes sure you know what a good rep looks like before you take it.
Frequently Asked Questions
Do I need a camera-based app if I already have a coach cueing me at the gym?
Not really — a coach's live cue is doing the same job a camera-based app does, just from a person instead of computer vision. Camera apps exist to fill that gap when you're training alone, which is most people, most sessions.
Can a cue-based app like Krato replace real-time camera feedback?
It solves a different failure mode. A cue-based app makes sure you know what correct form looks like and reminds you at the right moment; it won't catch a breakdown mid-set the way a camera watching your joint angles will. If you already know the cues and just occasionally break down under fatigue, a camera-based checker fills that specific gap.
Why do so many lifters have bad form even when they know the cues?
Knowing a cue intellectually and applying it under load, mid-set, on rep 7, are different skills. That's why pairing the cue with the actual set — not a separate tutorial you watched once — matters: the reminder shows up exactly when you need it, not whenever you happen to remember it.
Krato pairs every exercise with an expert coaching cue and adapts your plan session to session. Free on the App Store.