Many adults who write to me have already tried an app. Simply Piano, flowkey, Playground Sessions, Skoove: they are well made, they are encouraging, and for a few weeks they work. Then something stalls. The songs get harder, the hands get tired, and the progress bar stops telling you anything useful.
I am not against apps. I want you to know exactly what they do well and what they cannot do, so you can use one without paying for it later.
What apps do well
They get you started. The first sound, the first song, the first small victory. For an adult who has been putting off the piano for years, that matters enormously.
They check notes and timing. Through your device's microphone, or a cable from a digital piano, an app can tell whether you played the right key at roughly the right moment. That is real feedback, and it is available at eleven at night.
They keep you coming back. Streaks, stars and levels are designed by people who understand motivation very well. Used lightly, they help.
What an app cannot see
Your hand. Whether the fingers are curved or collapsed, whether the thumb hangs off the keyboard, whether the wrist has sunk below the keys. An app hears that the note was correct. It does not see that you played it with a flat finger and a locked wrist. Those habits feel fine for months and then cap your progress, and sometimes they hurt. The wrist is the most common adult fault, and no app I know of can see it.
Your shoulders. Tension is silent to a microphone. It shows up as a raised shoulder, a held breath, a forearm that aches after twenty minutes. You may not notice it yourself; that is exactly why it needs eyes from the outside.
What an app cannot hear
The sound itself. Two people can press the same key at the same moment and produce completely different sounds: one harsh and thin, one round and singing. An app counts both as correct. A trained ear hears the difference instantly, and that difference is what people mean when they say someone "really plays." I wrote about this in you can play all the right notes and it still sounds wrong.
The balance between the hands. The melody should sing above the accompaniment. An app hears both hands as a list of correct notes.
The reason for a mistake. An app can tell you that bar twelve went wrong. It cannot tell you that it went wrong because your fourth finger was preparing too late, two bars earlier. A teacher's job is the why.
What an app usually skips
Most apps teach song by song. You follow colored notes, or a highlighted key, and you play. It is efficient for the first song and inefficient for the hundredth, because you never learn to read music independently, and every new piece starts again from zero. Reading takes weeks, not years, when it is taught in the right order. That order matters more than most adults realize, which is why different schools of teaching spend so much thought on it.
How to use an app well, if you use one
Treat it as a practice partner, not a teacher. Use it for drilling notes and rhythm. Get your hand position, your sound and your reading from somewhere that can actually see and hear you.
Film your hands once a week. Prop your phone at the side of the keyboard, level with the keys, and record a minute. Watch it with the sound off. Are the fingers curved? Is the wrist level? Do the shoulders stay down? You will learn more from that minute than from a week of stars.
Learn to read alongside it. Twenty minutes of the app, ten minutes of real reading, every day. Start with the grand staff.
Stop chasing the streak when your hands hurt. No streak is worth a strained tendon. If something aches, read what hand pain at the piano means.
Signs an app has stopped helping you
You can play songs, but you cannot read a new one. If every new piece needs the app to show you the keys, you have learned songs, not music.
You only play in "wait" mode. Some apps offer a mode that waits for the correct note before moving on. It is useful for learning notes and harmful for rhythm if it becomes the only way you play, because real music never waits.
Your forearm aches after practice. That is a technique problem, and no score on a screen will show it.
You have been stuck on the same level for weeks. A plateau is normal; here is why month four feels like going backwards. But if the only advice available is "try again," you need a different kind of help.
Your playing sounds mechanical. Correct and even, but not like music. That is the moment to start working on sound, and sound is learned from a musician.
The one thing you cannot do alone
The hardest part of learning without a trained musician beside you is that you cannot hear yourself from the outside. That is not a weakness of yours; it is true of every pianist, at every level, including me. It is why I read and answer recordings: send me a minute of your playing and I will tell you, in writing, the one thing to change first. And if you want to learn in the order musicians are taught, from the first lesson, start here.
For more on what you can and cannot fix on your own, read learning piano without a teacher.