How to use it
- Choose a time control. Tap a preset such as 20 min + 5 × 30 s — the most common club setting worldwide — or enter your own main time, period count and period length below. Setting the period count to 0 gives plain sudden death; setting the main time to 0 starts you in byo-yomi from move one.
- Place the device beside the board. On a phone, lay it flat at the side within reach of both players. The upper half is rotated so your opponent reads it upright. On a laptop, share the keyboard: A or ← for one side, L or → for the other.
- Play your stone, then press your half. That stops your clock and starts your opponent's, exactly like pressing a physical clock.
- Watch for byo-yomi. When main time runs out the half turns amber, shows the running period and counts the periods you have left. The last ten seconds of each period tick audibly.
What it does, and what it does not
It implements one system properly rather than several badly.
It does: Japanese byo-yomi with periods that reset on a move in time and are consumed permanently on an overrun — including burning several periods at once when a single think runs long. Sudden death, by setting the period count to zero. Byo-yomi from move one, by setting the main time to zero. Tenths of a second under 20 seconds, as a tournament clock shows. A move counter, pause, reset and an audible tick for the closing seconds. It also pauses itself if the tab goes into the background, so nobody loses time to a locked phone.
It does not: Canadian overtime (no stone counter), Fischer bonus time, Ing, the NHK reserve format, a spoken countdown, or separate settings per player. A browser tab can also be covered by a notification or locked mid-game. Those are the reasons the app exists — but for trying byo-yomi at a real board, this is enough.
Test whether byo-yomi is implemented correctly
This clock is a convenient way to see the rule that most timers get wrong. Set the main time to 0, the period count to 3 and the period length to 10 seconds, then start playing:
- Press within a few seconds. The period jumps back to 10.0 and the count still reads 3×. A move in time costs you nothing — that is byo-yomi.
- Now let a period expire. The count drops to 2× and a fresh 10 seconds starts for the same move.
- Let all three run out and the clock flags — you have lost on time.
Apply the same test to any Go clock you are considering. If a move consumes a period, or the period keeps draining after you move, it is a delay mode with the wrong label. There is more detail on how byo-yomi works.
When the app is the better tool
A browser tab is fine for a quick game and a poor choice for a serious one: the screen can lock, a notification can cover the clock, and there is no stone counter or voice.
Byoyomi Timer keeps the screen awake, works in airplane mode, and keeps counting on the Lock Screen through a Live Activity. It adds Canadian overtime with a tappable stone counter, Progressive overtime, Fischer bonus time with an optional cap, Ing overtime and the NHK format, independent clocks for each player, pass buttons that stop the clock for counting, referee tools, sixteen themes, saved setups and history — and it reads the closing seconds aloud in Japanese, Korean, Mandarin, English or German.
Want the clock that cannot be interrupted?
Byoyomi Timer keeps the screen awake, works offline, counts stones for Canadian overtime and reads the seconds aloud.
Coming soon to the App Store