Metronome

Set the tempo and the beats to a bar. The click is synthesised in the page; nothing is downloaded and nothing is recorded.

120beats per minute

The click is scheduled against the browser's audio clock a quarter of a second ahead, not counted off a timer, so it does not drift. It stops when the tab goes to the background, because a throttled tab cannot keep time.

The words at this tempo

WordRange
Grave20–39 BPM
Largo40–59 BPM
Adagio60–75 BPM
Andante76–107 BPM
Moderato108–119 BPM
Allegro120–155 BPM
Vivace156–175 BPM
Presto176–199 BPM
Prestissimo200–299 BPM

These are the ranges this site uses; sources disagree by several beats a minute. Why they are printed rather than assumed.