Chess Tactics Board
Scan every legal first move from your FEN for observable events including checks, mates, captures and promotions. Mate in one is confirmed by checking whether the opponent has any legal reply after each move. You can also rehearse an authored line. The tool does not search two or more plies ahead, evaluate best moves, or prove a longer forcing tactic.
Key features
- Exactly six FEN fields with king, piece-count, castling and en-passant consistency checks
- Inspect all legal first moves for check, mate, capture, promotion, special moves and opponent replies
- Prove exact mate in one by checking every checkmating first move with zero legal replies
- Rehearse an authored line of up to 12 plies while preserving state on a different move
- Touch board, arrow keys and UCI text alternative with flip, undo and restart
- Current FEN plus strict version 1 JSON session export and import, processed locally
How to use
- Enter all six FEN fields and, optionally, up to 12 UCI plies such as e2e4 separated by spaces.
- Choose guided practice or free exploration, or load the original mate-in-one example.
- Select a piece and highlighted destination or type a UCI move. Choose queen, rook, bishop or knight on promotion.
- Analyze the current board to inspect objective events and reply counts for every legal move. Select a result to play that exact move on the board.
- Inspect the state and SAN/UCI record, then undo, restart or save the current FEN.
- Export or import a session JSON file to revalidate the start position and every recorded move.
Use cases
- Demonstrate an original mate-in-one position during a lesson
- Check whether a copied FEN permits castling, en passant or promotion
- Rehearse a short legal line authored by a friend without remote submission
- Check an imported FEN for the existence and candidates of mate in one
Frequently asked questions
Does it find the best tactical move?
It scans every legal first move and marks mate in one only when the resulting position is checkmate with no legal opponent reply. It does not evaluate or rank moves, search mate in two, or prove longer forcing tactics, so it does not claim a best move.
Which FENs can I load?
It accepts exactly six standard FEN fields for the 8×8 pieces, side, KQkq rights, en-passant target, halfmove clock and move number. It rejects missing kings, a checked king belonging to the side that just moved, inconsistent rights and bad en-passant data; it cannot prove the entire historical reachability of every position.
How do checkmate and stalemate differ?
Check means the side to move has an attacked king. No legal moves with check is checkmate; no legal moves without check is stalemate. Repetition, 50-move claims, agreed draws and other tournament adjudication are outside this tool.
How do I enter promotion, castling and en passant?
Selecting a promotion destination on the board opens four piece choices. In UCI text, append q/r/b/n, for example a7a8q. Castle by moving the king and capture en passant by selecting the pawn's legal destination.
Is the guided answer hidden in my save file?
No. The practice JSON stores the starting FEN, authored expected line and played moves in plain text. Files are created or read only at your request and are not uploaded.
Privacy
Positions and moves are calculated in browser memory. JSON and FEN files are created only when you download them, and imported files are not sent to a server.
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