Chess with the whole rule book actually in it — castling that won't let you pass through check, en passant only on the very move it's allowed, stalemate told apart from checkmate, the fifty-move rule — against an opponent you can set anywhere from one that hangs pieces to one that won't give you anything.
The goal
Trap the other king. A king is in check when a piece attacks it, and the player in check must get out of it — move the king, block the line, or take the attacker. If there is no legal way out, that's checkmate and the game is over.
You never actually capture a king. Every legal move here is filtered so that it doesn't leave your own king in check, which is why a piece that's pinned against your king will refuse to move even though the square it wants looks empty. That isn't the board being awkward; it's the rule.
How the pieces move
- PawnOne square forward, or two from its opening square. Captures diagonally only — the one piece that takes in a different direction from the way it walks.
- KnightAn L: two squares one way and one square across. The only piece that jumps over anything in the way.
- BishopAny distance diagonally. It never leaves the colour of square it started on.
- RookAny distance along a rank or a file.
- QueenRook and bishop together — any distance, any straight line.
- KingOne square in any direction, and never onto a square that is attacked.
Tap a piece and every square it can legally reach is marked, so you never have to argue with the board about whether something is allowed. If a move you expected isn't offered, the reason is almost always a pin you hadn't spotted.
The three rules people forget
Castling
The king steps two squares toward a rook and the rook hops over to the other side of it — the one move where two pieces go at once. It's only legal if neither piece has moved yet, the squares between them are empty, and the king is not in check now, does not pass through check, and does not land in it. Castle by moving the king two squares; the rook follows on its own.
En passant
When a pawn uses its two-square opening move to slip past a pawn that would have been able to take it, the opponent may capture it as though it had only moved one — but only on the very next move. Wait a turn and the right is gone for good. It's the rule most often played wrong, and it is enforced properly here.
Promotion
A pawn that reaches the far rank becomes another piece, and a picker opens so you choose. It's a modal on purpose rather than an automatic queen: a rook or a knight is occasionally the right answer, and a knight that arrives with check is a real move, not a curiosity.
How a game ends
- Checkmate — in check with no legal move. Somebody won.
- Stalemate — not in check and no legal move at all. A draw, and the single most common way a winning position gets thrown away.
- Threefold repetition — the same position, with the same options, three times.
- Fifty moves — fifty moves each with no capture and no pawn moved.
- Insufficient material — neither side has enough left to force mate. King and bishop against a bare king is a draw whatever either player does.
- Flag falls — if you're playing with a clock, running out of time loses. Unless the other side couldn't have mated you anyway, which is scored as a draw.
Controls
- Tap, then tapThe piece, then where it goes. The legal squares light up in between.
- Or drag itPick the piece up and drop it. Same move, whichever feels better.
- UTake the last move back. Against the computer it takes back the pair, so it's your turn again.
- FFlip the board and look at the position from the other side.
- NStart a new game.
- EscDrop the piece you have selected. In the settings sheet, it closes it.
- GearOpens the setup sheet — opponent, difficulty, colour, clock and the look of the board.
Above and below the board you get each side's captured pieces and the material difference, so you can see at a glance who is up and by how much without counting the wreckage yourself. The move list runs alongside in ordinary chess notation.
The two modes
Versus the computer
Pick a difficulty and a colour — White, Black or Random — and play. The search runs on its own thread, so even when the opponent takes a full second to answer on the hardest setting, the page stays alive: the board still scrolls, the clock still ticks, and nothing freezes under your thumb.
Pass and play
Two people, one device. The extra choice here is what the board does between turns: Flip each turn so the board always faces whoever is about to move, or Stay put with White at the bottom the whole game, which is the better setting if you're both sitting on the same side of the table.
Pass and play keeps its own separate record, so a couple of games with someone else never touches your score against the computer.
The three difficulty levels
The difference between them isn't one dial being turned up. What actually changes is how deeply the opponent looks and — the part that matters most — whether it bothers to check what happens after a capture.
Beginner
Looks two moves ahead and does not follow captures through to the end of the exchange, so it sees that it can take your bishop and not that you take its queen back. That is genuinely how a new player loses pieces, which is why it was built this way instead of by giving a strong engine a dice roll — the dice version plays four good moves and then something deranged, and that's much more irritating to sit across from. Beginner hangs pieces, and it hangs them for reasons you can see.
Intermediate
Four moves deep, and it does follow the exchanges, so free pieces mostly stop appearing. It will still take a slightly-worse move over the best one now and then, and about one move in twenty it just plays something reasonable rather than something good. That's a real opponent for most people: it punishes a hanging piece immediately, and it can be beaten by a plan that takes more than four moves to arrive.
Hard
No slack and no mistakes. It searches as deep as it can get in about a second, keeping the best move it has found at each depth before going deeper, so it always has a real answer ready. It sees repetitions coming, it will not walk into a fork, and it does not hand anything back. Beating it takes a genuine plan.
A take-back is not cheating, it's how you learn. Play Hard, and every time it punishes something, press U and find the move you should have played instead. That's worth more than ten games against Beginner.
The clock
Off by default. When you want one there are four: Blitz at five minutes a side, Rapid at ten, and two with an increment — 3 | 2 and 5 | 3 — where every move you complete adds two or three seconds back to your own clock. The increment is what stops a won position turning into a scramble; if you've never played with one, start there rather than with Blitz.
How the board looks
Two independent choices. Squares sets the surface — Marble, Inlaid, Wood or Plain — and Look switches the pieces between Lamplit and Classic. Both are purely cosmetic, and they are the only two settings in the sheet that will not throw away a game in progress: change your mind about the wood halfway through and you keep the position. Everything else in the sheet starts a clean game, because it has to.
Tips
Get the middle, then get your pieces out
The four central squares are worth more than any others because a piece standing on or near them reaches more of the board. Push a central pawn, bring out a knight and a bishop, and castle — that's the opening, and it's the same opening every time. Moving the same piece three times before the rest have moved once is the most common way to be lost by move fifteen.
Castle earlier than feels necessary
A king in the middle is a target, and the game usually opens up before you expect it to. Castling takes one move, tucks the king behind pawns, and puts a rook where it can actually do something. Do it in the first ten moves unless there's a concrete reason not to.
Leave the queen at home for a while
Bringing the queen out early feels aggressive and mostly isn't: every minor piece that attacks her forces her to move again, and you develop your opponent's position while you run away. Let the knights and bishops go first.
Before you move, look for checks, captures and threats
Every time. Yours first, then theirs. Most blunders below club level are not deep positional errors, they're a piece that could simply be taken, sitting there in plain sight while both players think about something else.
Count the whole exchange, not the first capture
A pawn defended twice and attacked twice is not a free pawn. Follow the trade all the way to the end before you start it — this is exactly the difference between Beginner and Intermediate, and it's the difference between most human players too.
Watch for stalemate when you're winning
With a big material advantage, keep giving the other king somewhere to go until you're ready to mate. Queening a pawn and then leaving your opponent with no legal move and no check is a draw, and it stings.
Good to know
- A game in progress is saved on your device, so closing the tab or reloading picks it up where you left off. Changing a setting that affects the rules deliberately starts a fresh game instead.
- Two separate records are kept — one against the computer, one for pass and play — and a button in the setup sheet clears them when you want a clean slate.
- No account, and nothing is sent anywhere. Clearing your browser data clears your record, your settings and any game in progress.
- The opponent thinks on a background thread. If your browser refuses to start one, the game quietly falls back to thinking on the page instead — same moves, slightly less smooth.