Chessbot

The controls above the board are all you need:

• Play as – White or Black. Choosing a side starts a new game. As Black, the board is turned around and Chester opens the game.
• Skill – how hard Chester thinks. Your choice is remembered in this browser.
• Think – the time budget for each computer move, in milliseconds.
• New game – reset the board to the starting position.
• Computer move – ask Chester to move even when it is your turn.
• Undo – take back your last move and Chester’s reply.

Chester replies automatically after each of your moves.

There are two ways to move:

• Drag a piece to the square you want and let go.
• Click a piece, then click its destination. Click the piece again to deselect it.

Moves are checked by the engine, so illegal moves are simply refused. To castle, move the king two squares towards the rook — the rook follows automatically. En passant is handled for you. A pawn reaching the last rank always promotes to a queen.

You can also type a move in the Move or FEN box at the bottom and press Send move, for example e2e4, g1f3 or e7e8q.

The skill menu sets how many moves ahead the engine looks before it commits. A shallow search sees fewer tactics, so it misses things a human would spot.

• Clueless – moves at random, no thinking at all. For the very youngest players.
• Pathetic – picks whichever move scores best right now, without considering the reply.
• Beginner – one move ahead. Takes free material, but leaves pieces hanging.
• Easy – two moves ahead. A gentle club beginner.
• Medium – three moves ahead, the default. A reasonable casual opponent.
• Hard – four moves ahead. Punishes loose pieces and simple tactics.
• Expert – as deep as the time budget allows, usually six to ten moves ahead.

On the strongest level, a larger Think value gives a better move. It is safe to change skill or thinking time in the middle of a game; the next computer move uses the new setting.

To the right of the board is the same position written as text, the format Chester used when it played on Twitter. Each rank is eight characters and the board is drawn from your side:

• ♔ ♕ ♖ ♗ ♘ ♙ and their black counterparts are the pieces.
• ☐ is a light square and _ is a dark square.
• The first line names the side to move, and the last line gives the files (abcdefgh, or hgfedcba when you play Black).

The panel is rendered in a monospace font so every character occupies one cell and the ranks line up.

Under the board, Moves shows the game in standard PGN notation, including the final result. The FEN box holds the current position: copy it to save a game, or paste any FEN and press Set position to analyse or continue from there.

Click Analysis: Off to let the engine study the current position as long as it likes. The line under the board shows the depth reached, the engine’s evaluation in centipawns and the move sequence it expects. Click the link again to stop and carry on playing.

Positive scores favour White, negative scores favour Black. A score near zero means the position is balanced.

The status line above the board reports check, checkmate and draws, and the PGN ends with the result (1-0, 0-1 or 1/2-1/2). Chester agrees a draw for stalemate, the fifty-move rule, threefold repetition and positions where neither side has enough material to mate. Once a game is over, moves are refused until you press New game or Undo.

Chester is also a bot on Bluesky (@chessbot.bsky.social). You can play in the app or in a browser, and games are public posts that followers can watch.

Solo game

• Post or reply: new w 3 @chessbot.bsky.social — side (w/b) and skill (1–10).
• Chester replies with the board. Reply with your move as from-square to-square, e.g. e2e4.
• Chester answers each move. Use help in the thread for the full command list.

Play a friend — Chester referees

Mention Chester and your playing partner in the same post. Chester offers to referee: you are White, your partner is Black.

• Post: @chessbot.bsky.social @peter.bsky.social fancy a game?
• Each player replies accept (reply swap first to change colours).
• Take turns replying your move, e.g. e2e4. Chester records the moves, enforces turns, and announces check, checkmate, resignations and draws.
• Commands: resign, draw / accept / decline, score (head-to-head record), rematch (colours swap).

Chester never plays a side in a friend game — it only keeps the board and the score. See the Bluesky section above for a quick start.

Chester started life as @chess_robot, a Twitter bot that accepted a move by tweet and replied with a text board. It now lives on Bluesky as @chessbot.bsky.social, where you can play solo or invite a playing partner and let Chester referee. Just post "new w 3 @chessbot.bsky.social" to start a game.

Everything happens in your browser: no positions, moves or accounts are sent anywhere. The only thing stored is your skill preference, kept in this browser’s local storage.