Checkmate Checker
Set up a position or paste a FEN. The checker tells you at once whether it is checkmate, stalemate, check or a draw by insufficient material, counts the legal moves and lists every mate in one.
Need the best move rather than a verdict? The chess calculator runs Stockfish 19 on any position.
Load an example position
Drag a piece, or tap it and then tap a square. Drop a piece off the board to remove it. With a keyboard, use the arrow keys and Enter.
Back-rank mate in 1. Black's king is boxed in by its own pawns on f7, g7 and h7, so a rook check on the 8th rank is mate. White to move.
Result
No check
White to move. The position is legal.
White's king is not in check and White has 20 legal moves, so the game goes on.
- Legal moves
- 20
- Checking moves
- 1
- Mates in 1
- 1
Mate in 1 for White
Press a move to play it on the board.
Check a FEN
Paste a full FEN, or just the board part (the side to move comes from the switch above the board).
What Counts as Checkmate
A king is in check when an enemy piece attacks it (FIDE Laws, Article 3.9.1). It is checkmate when the king is in check and its side has no legal move left to get out of it. The game ends there: the player who gave mate wins (Article 5.1.1). The king is never actually captured.
There are only three ways out of a check:
- Move the king to a square no enemy piece attacks. The king may capture on the way, but only an undefended piece.
- Capture the checking piece with any piece, as long as that capture does not expose your own king.
- Block the line by putting a piece between the king and a checking rook, bishop or queen. Knight and pawn checks cannot be blocked.
In a double check, two pieces attack the king at once, and only a king move can answer it. If none of the three works, it is mate. Load the Check, not mate example above to see the difference one pawn makes: after Rd8+ the pawn on h6 has given Black's king the escape square h7, so Kh7 is legal and the game goes on. Without that pawn move, the same Rd8 is the back-rank mate in the first example.
Checkmate, Stalemate, Check or Draw?
Two questions decide every position: is the king of the side to move attacked, and does that side have a legal move?
| Position | King attacked? | Legal moves? | Result |
|---|---|---|---|
| Check | Yes | At least one | The game goes on; the reply must end the check |
| Checkmate | Yes | None | The side that gave mate wins |
| Stalemate | No | None | Draw (Article 5.2.1) |
| Insufficient material | Either | Any | Draw: no mate is possible (dead position, Article 5.2.2) |
Stalemate is the classic way to throw away a won ending. With Black's king on a8, White's king on c6 and the queen on b1, Qb7# wins but Qb6 leaves Black with no move and no check. The Mate or stalemate? example lists both. The basic endgames guide shows how to drive a lone king to the edge without falling into it, and the lesson on stalemate rules and traps covers the positions where it happens most.
How the Checker Decides
- It reads the position. From the board or a FEN, which can be complete or just the piece placement such as 6k1/5ppp/8/8/8/8/5PPP/3R2K1. A broken FEN gets a message naming the field and rank at fault.
- It checks the position is legal. Exactly one king each, no pawn on the 1st or 8th rank, and the side that just moved is not in check. Castling rights are dropped when the king or rook has left its square, and an en passant square is kept only if a pawn really could have just moved two squares past it.
- It generates every legal move for the side to move with chess.js, an open-source move generator, including castling, en passant and every promotion.
- It gives the verdict. In check with no legal move is checkmate. Not in check with no legal move is stalemate. Material that can never mate is a draw. In check with moves left is check, and the checker sorts the replies into king moves, captures and blocks.
- It tries every move once. Each legal move is played and the resulting position checked, which finds every mate in one and every move that would stalemate the opponent.
It also warns about positions that are legal to analyse but impossible in a real game, such as a side with nine pawns, more promoted pieces than missing pawns, or a king attacked by three pieces at once. It does not search beyond one move, does not know the game's history (so it cannot see a threefold repetition), and only reports a 50-move draw when the FEN's half-move clock says so. Everything runs in your browser; the position is never uploaded.
Checkmate Patterns to Recognise
Most mates in real games are one of a handful of shapes. Each one below is an example you can load into the checker.
Back-rank mate
A rook or queen checks along the last rank while the king's own pawns block its escape. White plays Rd8# against a king on g8 with pawns on f7, g7 and h7. The cure is to make a flight square in advance: h3 for White, ...h6 for Black.
Scholar's mate
1.e4 e5 2.Bc4 Nc6 3.Qh5 Nf6?? 4.Qxf7#. Queen and bishop hit f7, which only the king defends. After 3.Qh5, either 3...g6 or 3...Qe7 stops it.
Fool's mate
1.f3 e5 2.g4 Qh4#, the fastest mate there is. Moving the f- and g-pawns opened the e1-h4 diagonal, and no white piece can reach f2 or g3 to block it.
Smothered mate
A knight mates a king surrounded by its own pieces. In Philidor's Legacy, White's queen is on c4 and knight on g5, Black's king on h8 and rook on a8: 1.Nf7+ Kg8 2.Nh6+ (a double check) Kh8 3.Qg8+! Rxg8 4.Nf7#. The queen sacrifice forces the rook onto the king's last free square.
For more shapes and how to set them up, see the checkmate patterns every player needs, then practise spotting them under time pressure in chess puzzles.
Find the Best Move Instead
The checker answers one question: is the game over, and is there a mate in one? When it says "no mate in 1", the position still has a best move. Set the same position up on the chess calculator and Stockfish 19 finds it, with an evaluation that tells you whether the position is winning, equal or lost. Pro members can paste the FEN straight in instead of placing the pieces.
Frequently Asked Questions
How do I know if a position is checkmate?
It is checkmate when the king is in check and the side to move has no legal move. Test the three ways out of check: can the king step to a square that is not attacked, can the checking piece be captured, can another piece block the line? If all three fail, it is mate. The checker above tries every legal move, en passant captures and promotions included.
What is the difference between checkmate and stalemate?
In checkmate the king is attacked and there is no legal move, so the side that gave mate wins. In stalemate the king is not attacked but there is still no legal move, and the game is a draw (FIDE Laws, Article 5.2.1). With White's king on c6, White's queen on b1 and Black's king alone on a8, Qb7# is mate but Qb6 is stalemate.
Is it checkmate if the king can capture the checking piece?
No, as long as the capture is safe. If the king can take the checking piece and the square it lands on is not attacked by another enemy piece, the check is answered and it is not mate. In Scholar's mate, after 4.Qxf7# the black king cannot take the queen because the bishop on c4 protects f7, so it is checkmate.
Can a king give check or checkmate?
No. A king can never give check itself, because kings may never stand next to each other. A king move can uncover a check from a rook, bishop or queen standing behind it, and that discovered check can be checkmate.
Why does the checker say my position is illegal?
It refuses three kinds of position: a side without exactly one king, a pawn on the 1st or 8th rank, or the side that just moved still standing in check, which no legal move can leave behind. The last one usually means the wrong side is set to move, so change the side to move above the board. Positions that could never come from a real game but can still be analysed, such as one with nine pawns, get a verdict plus a warning.
Does the checker find mate in 2 or longer?
No. It plays each legal move once and reports the ones that mate at once, which is exact and instant. For a mate in two or more, or the best move in any position, set the position up in the chess calculator and let Stockfish 19 search it. Pro members can paste the FEN straight in.
What does insufficient material mean in chess?
It means neither side can checkmate by any series of legal moves, so the game is drawn at once. The checker flags the standard cases: king against king, king and bishop or king and knight against a lone king, and positions with only kings and bishops where every bishop stands on squares of one colour. King and two knights against a king is not a draw by rule, because mate is possible if the defender blunders.