Chess: a serious opponent you can open in a tab

01  What it is

Chess is a single-player game against a computer opponent that runs entirely inside your browser tab. No account, no download, no sign-up wall, and no game server: the position, the rules and the search all live on your own device. Open the page and you are two taps from a game.

The board is built phone-first and orients to whoever you chose, so your pieces sit at the bottom with the file letters and rank numbers printed on the board edges. Tap a piece and its legal moves light up — a dot where it can move, a ring where it would capture — then tap the destination, or just drag it. Drag works with a mouse and with a thumb, and the pieces are drawn from our own vector Staunton set.

This is not a chess platform. There is no rating, no ladder, no games database and no human opponent here. It is one good game against a decent engine, in the time it takes a heavier site to finish loading.

02  The four opponents, and what actually changes between them

Easy, Medium, Hard and Master are the same engine — same rules, same code, same evaluation. What changes is how long it is allowed to think, and whether it is allowed to go easy on you. Easy is capped at a two-ply search with a 200 ms budget, and on roughly three positions in ten it skips the search and plays a random legal move instead of its best one: this is the level that leaves pieces where you can take them. Medium gets three plies in half a second and no random moves at all. Hard gets four plies and about 900 ms. Master — for players who have run out of Hard — gets up to seven plies on a budget of about 2.4 seconds.

Those extra plies are not just a bigger number. It keeps a transposition table keyed by a Zobrist hash, so a position reached by two different move orders is not analysed twice, and it remembers which replies refuted a line so it tries them first — that is what makes the pruning cut so much more. It resolves captures at the very leaves, so it never stops counting in the middle of a trade.

The honest ceiling: the evaluation is material plus piece-square tables, and that is all of it — no opening book, no endgame tablebase, no pawn-structure or mobility term anywhere in the code. It plays the opening by searching rather than by knowing, so a strong club player will still beat Master.

03  It plays the real rules, including the tedious ones

Castling, en passant and promotion are all in, and they work the way they do on a board: castle by moving your king two squares toward the rook, capture en passant onto the highlighted square, and when a pawn reaches the far rank a small panel asks which piece you want, with a cancel if you change your mind. Check is shown on the board, with the attacked king's square marked.

Checkmate and stalemate are both detected, along with the three draw rules most casual implementations skip: threefold repetition, the fifty-move rule (a hundred half-moves with no pawn move and no capture), and insufficient material — bare kings, king against a lone knight or bishop, or king and bishop against king and bishop on same-coloured squares. One difference from a real board: those draws are declared, not claimed, so playing into a third repetition ends the game the moment it happens.

Move generation is where a chess program quietly gets things wrong, so it is tested hardest: the suite walks the legal move tree from the starting position to depth three and checks the node counts against the known correct values (20, then 400, then 8,902). The engine draws its moves from the same generator your own pieces do, so it cannot cheat you by construction.

04  Tap, drag, undo, and what the board tells you

Both input styles work on both kinds of screen. A tap selects and a second tap moves; a press-and-drag moves the piece directly, and only counts as a drag once your finger has travelled a few pixels, so an unsteady tap does not fling a piece across the board. The last move is highlighted, so you can see what just happened without replaying it in your head. If you prefer the keyboard, every square is focusable, playable with Enter or Space, and labelled for a screen reader.

Undo is the feature people actually lean on. It takes back your move and the engine's reply together, landing you at your own turn in the position as it was — not stuck mid-exchange waiting for a reply that no longer makes sense. There is no limit and no penalty; it is out of reach only while the engine is mid-think. Use it to test an idea, watch it fail, and try the position a different way.

"New game" re-opens the side-and-difficulty panel over the board rather than resetting behind your back, and if you play as Black the engine makes the first move. Your last choice of side and difficulty is remembered on the device, so a rematch is one tap — and the engine thinks off the main thread, so even Master's two-and-a-half seconds never freezes the board.

05  How to actually beat it

Because the opponent is a material count and a piece-square table, some habits work better here than they would against a person.

• Do not offer material hoping it will not notice. From Medium up, anything winnable by a capture will be won.
• A sacrifice that buys lasting compensation is mis-scored in your favour, because compensation is not something this evaluation can see — but you have to genuinely have it.
• Positional pressure is the most reliable way to outplay Master. It has no term for pawn structure, mobility or piece coordination, so a squeeze that never offers a capture is exactly what it cannot measure.
• Do not try to hold a draw by shuffling. Its king evaluation switches from "hide behind the pawns" to "march to the centre" as material comes off, so it walks its king into the ending and tries to convert.
• Its null-move pruning is switched off in the endgame, so zugzwang is handled correctly — do not plan around forcing it to move when every move loses something.
• Against Easy the whole game is patience: take what it leaves, leave nothing of your own, and let the random moves do the work.

06  When it ends: the card

Every finished game ends on a card showing the result, how it ended, how many moves it took and which opponent it was — "Checkmate in 24 · beat Hard", or the less happy version. Behind it is a 1080×1350 image rendered from the actual final position, your pieces exactly where you left them, which you can download as a PNG or hand to your phone's share sheet.

Nothing is signed up for and nothing is synced. The only thing the game remembers is your last side and difficulty, stored in your own browser. It is free and supported by one ad slot below the board and its controls, never on top of the position you are trying to read.

07  Questions people ask

Is this chess game free, and do I need an account?

Free, and no account. There is no sign-up, no login, no download and no paywall on any part of the game. It is supported by one ad slot below the board, and it runs entirely in your browser — pick a side and a difficulty and you are playing.

How strong is the computer opponent?

Four levels, one engine. Easy searches two plies deep with a 200 ms budget and plays a random move about three times in ten, so a beginner can win it. Medium and Hard add depth and remove the deliberate mistakes. Master is allowed seven plies and about 2.4 seconds. It is a material-and-position evaluation with no opening book or endgame tablebase, so a strong club player can still beat Master — a real opponent, not an unbeatable one.

Can I play as Black, and who moves first?

Yes. Choose Black at the start and the board flips so your pieces are at the bottom, and the engine plays the first move as White. Your choice of side is remembered on the device, so your next game starts the way you left it.

Can I undo a move?

Yes, and undo takes back the engine's reply along with your move, so you return to your own turn in the position as it was. It is available at every level with no limit and no penalty, and it is unavailable only while the engine is still thinking.

Can I play against a friend, or online?

No — this version is single-player against the computer only. There is no online multiplayer, no matchmaking and no way to play another person, and there are no chess clocks or time controls either. It is one game against the engine, on your own device.

Does it work on a phone, and does it need to be online?

It is built phone-first: the board fits a small screen without pinching or scrolling, and you can move by tapping or dragging. The page needs to load once over the network; after that the game, the engine and your result card all run locally in your browser, and nothing about the game is sent anywhere.

08  More from the shelf

• Tilewright — Draw seven tiles. Outword the AI.
• Dominoes — Match the ends. Block them out.
• Backgammon — Roll the race. Take the cube.
• Fiveaside — Score past the keeper. Post the scoreline.

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