Write notes on a grand staff and hear them straight away. Nothing to install.
Click the staff to place a note at that pitch. Pick the length in the note panel, where dots, accidentals and ties live too.
You can type as well. A to G give the pitch, 1 to 6 the length, the up and down arrows move the pitch, the left and right arrows move the cursor.
Slurs, dynamics, pedal and repeats come from the expression panel. For anything that spans a range, click the first note and then the last.
During playback the sounding notes light up. Your score stays in the browser, and you can move it in and out as JSON or MusicXML.