Set 20 to 300 BPM, pick a time signature, add subdivisions and tap in a tempo. Every click is timed on the audio clock.
A metronome plays a steady click at a set number of beats per minute (BPM), and this one runs from 20 to 300 BPM with a click that is placed on the audio clock instead of a page timer. The distance between two beats is 60 divided by the BPM in seconds, so 120 BPM is one beat every 0.5 seconds and 60 BPM is one per second. In 4/4 at 100 BPM a bar of four beats lasts 2.4 seconds. A short timer wakes up every 25 milliseconds and queues each click that falls in the next 0.1 seconds, giving each one an exact start time on the Web Audio clock. If the page is busy for a moment, the clicks already queued still sound at their exact times, so the spacing stays even. The tempo, time signature and subdivision are read again on every wake-up, so you can change them while it plays and hear the change from the next queued click.
The time signature sets how many beats make a bar: 2/4, 3/4, 4/4, 5/4, 6/8, 7/8, 9/8 and 12/8. The BPM always counts the note in the bottom number, so in 4/4 it counts quarter notes and in 6/8 it counts eighth notes. With Accent the first beat on, beat one of each bar is higher and louder. In 6/8, 9/8 and 12/8 every third beat also gets a medium click, which groups the bar as 3 + 3, 3 + 3 + 3 or four groups of three. Other signatures, 7/8 included, are not grouped, and you cannot set your own accent pattern. Subdivisions add softer clicks between beats: 2 per beat gives eighth notes in 4/4, 3 gives triplets and 4 gives sixteenth notes. At 90 BPM in triplets the clicks are 0.2222 seconds apart.
Tap tempo works out a speed from your taps. It averages the gaps between up to your last 8 taps and turns the mean gap into BPM, rounded to a whole number. Four taps at 0, 520, 1040 and 1560 milliseconds have a mean gap of 520 ms, which is 60,000 divided by 520, or 115 BPM. A pause of more than 2 seconds starts a new count, and one tap alone changes nothing. When no field or button has focus, Space starts and stops, Left and Right change the tempo by 1, Down and Up change it by 5, and T taps. Typing in the tempo box or using the slider works as well, and the value is always held between 20 and 300.
The presets from Largo to Presto use the BPM ranges listed on English Wikipedia's Tempo page: Largo 40 to 66, Adagio 44 to 66, Andante 56 to 108, Moderato 108 to 120, Allegro 120 to 156, Vivace 156 to 176 and Presto 168 to 200. Those ranges overlap, and sources disagree, so a preset sets the middle of its range and the page lists every name that fits the current tempo. This metronome has no swing, no polyrhythms, no tempo ramps and no saved songs. Wireless headphones delay all sound, so the click can seem to lag behind your playing even though the spacing between clicks is exact. The page asks the browser to keep the screen on while it runs, where the browser allows it.
Press Tap tempo, or the T key, in time with the music at least twice. The tool averages the gaps between your last 8 taps, so 4 taps 520 ms apart give 115 BPM. If you stop for more than 2 seconds the next tap starts a new count.
Choose 6/8 under Time signature. The bar has 6 beats and the BPM counts eighth notes. With Accent the first beat on, beat 1 is the strongest click and beat 4 gets a medium click, so you hear two groups of three.
It is built to. While the tab is hidden the page queues clicks 1.5 seconds ahead instead of 0.1, because a browser may run a hidden tab's timers only about once a second. A tempo change is then heard up to 1.5 seconds late. If you need to change tempo often, keep the tab visible.
Open Subdivisions, accent and volume and choose 3 per beat for triplets or 4 per beat for sixteenth notes in a quarter-note beat. The sub clicks are softer and lower than the beats. At 120 BPM, 4 per beat puts a click every 0.125 seconds.
Wikipedia's Tempo page lists Andante as 56 to 108 BPM and Allegro as 120 to 156 BPM. The ranges overlap with their neighbours, so the presets set the middle of the range: 82 for Andante and 138 for Allegro.
Nothing is uploaded. The clicks are made in your browser with Web Audio, and no server receives anything. Your tempo, time signature, subdivision, accent and volume are saved in this browser so they are there next time. The page counts visits with Google Analytics, never your settings.