# Chess clock

> How much time does each player have? Two chess clocks with increment or delay, a move counter and a flag at zero.

Free online chess clock for two players: blitz, rapid and classical presets, increment or delay, move counter and a flag. Works full screen on a phone.

- Page: https://how.box/en-us/datetime/chess-clock/
- Runs entirely in the browser.

## Inputs

Answer link: https://how.box/en-us/datetime/chess-clock/?m={m}&i={i}&t={t}

- `m` (whole number 1 to 180): Starting time per player in whole minutes, 1–180. Never starts a clock. Example: `10`.
- `i` (whole number 0 to 180): Seconds per move, 0–180. Example: `0`.
- `t` (increment or delay): increment (added after each move) or delay (counted down before the clock runs). Example: `increment`.

Example answer: https://how.box/en-us/datetime/chess-clock/?m=10&i=0&t=increment

The page computes the answer in the browser: read results from the agent tools below, not from the page HTML.

## Agent tools

- `chess_clock_time_budget`: The time one player has under a chess time control.
  - MCP, one POST to https://how.box/mcp: `{"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"chess_clock_time_budget","arguments":{"base_minutes":10,"increment_seconds":0,"mode":"increment"}}}`
  - GET: https://how.box/mcp/run/chess_clock_time_budget?base_minutes=10&increment_seconds=0&mode=increment

## How it works

A chess clock gives each player the same total thinking time. Only the clock of the player to move runs; when they make their move and press their button, their clock stops and the opponent's starts. A player whose time runs out loses on time, which is called the flag falling.

Most games add a little time per move. With an increment (Fischer), the seconds are added to your clock after each move, so you can never lose time by moving fast. With a delay, the clock waits for the seconds at the start of each turn and only then counts down; unused delay is lost. A control is written base plus seconds: 3+2 is 3 minutes with 2 seconds per move. For example, with 90+30 and 40 moves, a player can use up to 90 × 60 + 40 × 30 = 6,600 seconds, or 110 minutes.

This clock does not know the rules of a tournament, such as extra time after move 40, and it does not check the moves. It keeps counting after a reload, but it is a convenient clock for casual play, not an arbiter.

## FAQ

**What is the difference between increment and delay?**
An increment adds time to your clock after every move, so a quick move can even gain time. A delay just postpones the countdown at the start of your turn; if you move within the delay, your clock does not change.

**Who starts?**
White. Select Start or press Space and White's clock runs. After White moves they select their side and Black's clock starts.

**What happens at zero?**
The clock stops, the flag falls for that player and the other clock stays where it was. Select Reset for a new game.

**Does it keep running if I lock the phone?**
The time keeps counting and shows the right value when you return, but a sound only plays while the page is visible. Use full screen to keep the display awake.

**Does the clock add extra time after move 40?**
No. It uses one time control throughout the game. Multi-stage tournament controls are not supported.

More: [HowToolbox index](https://how.box/llms.txt) · [agent guide](https://how.box/agents.md) · [agent terms](https://how.box/en-us/about/agents/)