gizmobench

Chess Clock

Two clocks, one press to pass the move. Set a base time in minutes, choose increment, delay or sudden death, and the rule is applied the way a tournament clock applies it: the increment is paid to the side that has just completed a move and never to the side still thinking, and the delay is granted once at the start of a turn and what goes unused is not carried over. Each side's remaining time is worked out from the timestamps of the presses rather than counted down frame by frame, so a tab in the background, a locked phone or a slow browser cannot quietly give the thinking player their time back, which is what a general countdown page on this search gets wrong. Undo steps back one press and holds both clocks while the position is sorted out.

White 5:00 · Black 5:00 · not started · 5 min + 3 s increment

Mode
Layout

Base time is in minutes: 5, 2.5, or 1:30 for a minute and a half. The seconds field is the increment added after a move is completed, or the delay granted once at the start of a turn.

Common time controls

Ready. Press Start, then pass the move with the big button, a tap on your own half, or the space bar.

The shortcuts wake up once you have clicked or tabbed into the clock, and only while it is on screen. Until then the space bar pages the article down, the way it does everywhere else.

What a move costs

Worked by the same code the clock runs on, from a five minute base time.

  • Increment 3 sa 2 second move1 s added
  • Delay 3 sa 2 second moveno change
  • Delay 3 sa 5 second move2 s off the clock
  • Sudden deatha 5 second move5 s off the clock
Timed against the clock, not the frame rate. Each side's remaining time is worked out from the timestamps of the presses, so a backgrounded tab, a locked phone or a slow animation frame does not hand anyone time back: the first reading after the page wakes is the right one. Increment is added after a move is completed and delay is applied once at the start of a turn, which is the difference that decides close endings.
Accuracy. Both clocks are worked out from real timestamps rather than from animation frames, so a backgrounded tab or a locked phone does not return time to either player. Increment is added after a move is completed and delay is applied once at the start of a turn. It is a clock only: it does not know the position or the rules. Undo steps back one press at a time and holds the clocks while you sort the position out, so the seconds spent noticing a mis-press are charged to nobody. The settings are remembered in this browser; a game in progress is not, because a clock restored halfway through a reload is a clock nobody could trust.

Common questions

What is the difference between increment and delay?
Increment is added to your clock after you complete a move, so a fast move can leave you with more time than you started the turn with. Delay is a grace period at the start of your turn during which your clock does not run at all; your clock never goes up, and any delay you do not use is gone when the turn ends. A turn therefore costs you the time you used minus the delay, and never less than nothing, which is the same amount the Bronstein rule leaves off the clock by running the clock and adding the used time back afterwards.
Does the clock keep time if the tab goes to the background or the phone locks?
Yes. Nothing is counted down: each side's time is the number it had banked when its turn began minus the wall clock time since the press, so the display can freeze for ten minutes and the first reading after the page wakes is still exactly right. A clock that subtracts a little on every animation frame loses whatever the browser did not deliver, and a hidden tab is not drawn at all.
How do I undo a press?
Press U, or the Undo button under the clocks. It steps back one press at a time and restores the clocks, the move counts and the side to move exactly as they stood when that button went down, then holds both clocks so the seconds spent noticing the mistake are charged to nobody. Press Resume when you are ready. A flag that has already fallen is not undone: the clock will not revive a game that ran out of time.
Can two people play on one device?
Yes, that is what it is for. Each half of the clock is its own button, so you tap your own side to pass the move, and the half that is not to move does nothing when pressed, the way a physical clock's buttons work. The Facing layout turns one half around so the two of you can sit across a table from the same phone or tablet. From a keyboard, the space bar passes the move, P pauses and U undoes.
What time control should I use?
The common ones are one tap away: 1+0 for bullet, 3+2 and 5+3 for blitz, a 5 minute game with a 3 second delay for club play, 10+0 and 15+10 for rapid, and 90+30 for classical. You can also type any base time from 1 second to 720 minutes, as minutes (5), as a decimal (2.5) or as minutes and seconds (1:30), with an increment or delay up to 600 seconds.
Does it know the rules of chess?
No. It is a clock: it counts time, applies the increment or delay, and shows which flag fell first. It does not see the board, does not know whose move is legal, and does not decide the result, because a player who flags when the other side cannot possibly mate has not lost the game. Nothing about the position is entered, stored or sent anywhere.
Is anything uploaded, and does it remember my settings?
Nothing is uploaded and there is no account: the clock runs entirely in the page. Your base time, mode, seconds and layout are remembered in this browser alone, so the clock opens on the control you last used. A game in progress is deliberately not saved, because a clock restored halfway through a reload is a clock neither player could trust.

Both clocks are worked out from real timestamps rather than from animation frames, so a backgrounded tab or a locked phone does not return time to either player. Increment is added after a move is completed and delay is applied once at the start of a turn. It is a clock only: it does not know the position or the rules.