How Chessdox works

1. A room is created for one game

When you press Create game, the server opens a room with its own game code and gives your browser a private seat key. The key is stored in your browser, not in the address bar, so the link you see can be shared or bookmarked without handing over your seat. Reloading the page, closing the tab or coming back later on the same browser puts you straight back at the board.

2. One invitation, used once

For a game against another person, Chessdox shows an invite link. It carries a single-use invitation: the first person who opens it and joins takes the second seat, and from then on the link can no longer claim a seat. If the link went to the wrong place, replace it before anyone joins and the old invitation stops working. Against the computer there is nothing to share; the engine takes the other seat immediately.

3. Every move is checked by the server

Your browser shows legal moves as soon as you pick up a piece, but the decision is made on the server. Each move is validated against the full rules of chess, including castling rights, en passant and promotion, before it is recorded and sent to your opponent. The server also detects check, checkmate, stalemate, threefold and fivefold repetition, the fifty- and seventy-five-move rules and positions where neither side can mate.

Because the server holds the official game, both players always see the same position, and a lost connection never loses a move. When you reconnect, the board catches up from the last confirmed state.

4. Clocks run on the server, too

With a time control, the server measures each player's thinking time and adds the increment after every move. Your browser displays a smooth countdown that is regularly corrected against the server, so the clock you see matches the clock that decides the game. The panel of the player to move lights up, and in the last seconds the clock turns red and shows tenths. Run out of time and the game is lost, unless your opponent has no way left to mate.

5. A board built for play

You can drag pieces or tap a piece and then its destination. Promotion asks which piece you want, premoves let you queue a reply while your opponent thinks, and right-click or a long press draws arrows and circles for planning. The arrow keys, the mouse wheel or a swipe step through earlier positions. Coordinates and move sounds can be switched on or off in the board settings, and those choices are remembered in your browser.

6. When the game ends

A game ends with checkmate, resignation, a draw by agreement or by rule, or on time. Both players can then download the complete score as PGN. Games between two people stay private for good. A finished game against the computer can be published as an anonymous replay if the public replay option was left on when the game was created; the replay contains the moves and the result, never a name you entered.

Published replays are collected in the replay library and grouped by opening, so you can see how a line you play turns out against the engine.