Is there an app that checks if I'm singing in tune?
Yes. Singsteady runs in your browser, listens through your microphone and measures every note you sing in cents (hundredths of a semitone). It plays a note on the piano, you sing it back, and you see how far off you were, flat or sharp, as you sing.
On 817 seconds of real singing, the pitch engine's median error per frame was 0.87 cents. The note averages it reports land within about 5–8 cents of studio analysis, which is far finer than the ±25 cents we treat as “in tune”.
More questions: How accurate is an online pitch or vocal range test? · What is a cent in singing? · Can you learn to sing in tune? · How do I find my vocal range? · How do I sing high notes without straining?