Keuwl Guitar Tuner is a free tuning app that helps you determine if your instrument needs to be tuned. It picks up sounds via your device's microphone, and it shows you three separate gauges for information about the sound or note. The three gauges are arranged from inside a circle to the outside, and the inside gauge measures octave. The middle gauge measures the name of the note, and the outer gauge measures the actual tune of the note and whether it is sharp or flat. There is an orange region around the perfect tuning of the note that comes within 10 cents of the correct tuning, and the internal green section covers a more accurate 5-cent range.

This app is completely free and has no ads or restrictions. As long as you give the app permission to use your device's microphone, it can do everything it offers with no other need on your end. You can even alter the tuner to work for other instruments. If you need to tune your instrument to something other than the standard 440Hz A, you can use the Shift function to maintain balanced tuning in a shifted position. The reset button will return to normal settings.