Choosing the best Go clock app

The tests, in order of importance

1. The byo-yomi reset test. Set a 10-second period, then complete a move in 5 seconds. The period must return to a full 10 seconds and the period count must not drop. If either fails, the app has a delay mode labelled byo-yomi. This is the single most common defect in the category.
2. The period count. Is the number of remaining periods on screen while you play? "You are in byo-yomi" is not useful information; "two periods left" is.
3. The stone counter. Select Canadian overtime. Are stones owed shown per player, do they decrement as the clock is pressed, and does the block refill at the quota? If Canadian is missing entirely, that is a legitimate choice — but know it before your club night.
4. Correcting mistakes. Can you adjust time, periods and stones mid-game? Real games produce mis-taps and miscounts, and an app without this forces a restart.
5. Independent players. Can each side have a different main time, a different period count, ideally a different system? Handicap and teaching games need it.
6. Behaviour under interruption. Does the screen stay awake for two hours? What happens on an incoming call? A clock that dims mid-game is unusable.
7. Ads and accounts. An advertisement during a two-hour game is disqualifying. So is an account requirement — a clock has nothing to synchronise.

What this app does

Measured against that list, Byoyomi Timer implements all seven systems Go is played under — Japanese byo-yomi, Canadian and Progressive overtime, Fischer bonus time with an optional cap, sudden death, time per move with NHK-style reserves, and Ing overtime — each with the display that system needs.

Byo-yomi periods reset properly and the remaining count is always visible. Canadian overtime has a tappable stone counter. Time, periods and stones can all be corrected mid-game. Both clocks are fully independent. The voice reads the last ten seconds of each period, the entry into byo-yomi, the final period and every lost period, in Japanese, Korean, Mandarin, English or German — set separately from the interface language, which is available in seventeen languages.

The screen stays awake, the clock continues on the Lock Screen through a Live Activity, and everything works offline with no account, no analytics and no advertising.

Where it is not the right choice

Being straightforward about the limits is more useful than a feature list:

• You need Android. This is an iOS app. It does not run on Android, and no amount of wanting will change that.
• You want a chess clock too. Bronstein delay and hourglass mode are deliberately absent, because Go does not use them. For chess, use a chess clock app.
• You want an online playing platform. This times a physical board. To play Go over the internet you want OGS, Fox, Tygem, IGS-Pandanet or KGS.
• You want a board scorer. It does not read the board, count territory or score the game. It measures time.
• You need a clock that cannot be interrupted at all. A phone is a phone. For a national championship, dedicated hardware remains the conservative choice.

Hardware, for comparison

Dedicated Go clocks are a small market. The best known is DGT's byo-yomi timer, sold specifically for Go and Shogi, on which both the period length and the number of periods are settable — worth knowing about, because most clocks that mention byo-yomi are not built for Go at all.

The trade-off is straightforward. Hardware is durable, cannot ring, and has a battery measured in months. A phone has a far better display — it can show a running period, the periods remaining, a stone counter and the system name at once, which a segment display cannot — and it can speak the countdown. Neither is strictly better; they fail differently.

Try before installing

The online Go clock on this site runs byo-yomi in a browser with no signup and no download. It is intentionally limited compared to the app — a browser tab can lock or be covered by a notification, and it has no stone counter or voice — but it is enough to run the reset test above and see whether a screen beside your board suits you at all.