Ocatune is a dynamic practice drone. It listens to the note you are currently playing on the ocarina, and plays the closest equal tempered note for you as a reference pitch.
By doing this, Ocatune makes it easy to hear intonation errors:
Note that you must use headphones, as Ocatune will behave very erratically if it can hear its own output.
When you click 'start' above, your browser will ask you for permission to use the microphone. Once you allow it, the tool will begin detecting the notes you are playing and play the closest in-tune note for you as a reference.
When you are playing in tune with the reference pitch, you will hear a clean sound, but if your pitch is flat or sharp you will hear a 'warbling' sound. What to listen for is demonstrated by the tool below. Notice how the sound changes when you drag the pitch slider left or right.
Ocatune has a few options to visualise the tuning of the note you are playing, in relation to the reference pitch. These are intended to help you understand how your intonation sounds when you are flat or sharp.
The Time between when you start playing, and when Ocatune starts playing the reference pitch is called 'round trip audio latency'. It varies from device to device, and tends to be lower on desktops and laptops than mobile devices in my experience.
Finding a device with lower latency is highly desirable, as higher latency limits your playing speed.
Note that pitch detection using the built in microphone in a laptop or other device with a fan may be unreliable due to noise. In such cases using an external microphone should work better.