Guide · Using the finder
Setting Up a Chess Position for Analysis
A move finder is only as good as the position you give it. One pawn on the wrong square, the wrong side to move or a castling right that no longer exists can change the best move completely. This guide covers the editor, the FEN format and the mistakes that make an engine refuse a position or answer the wrong question.
If you review games you played online, ChessHelper (chesshelper.ai) shows its suggestions directly on Chess.com and Lichess analysis boards, so there is nothing to copy by hand. For a position from a book, a photo or an over-the-board game, use the editor on our move finder as described here.
Placing pieces with the editor
The finder opens in play mode, where tapping or dragging makes legal moves. To edit, choose a piece in the palette. The board gets a blue frame to show you are editing.
- Place: tap a square to put the selected piece there. Tapping a square that already holds the same piece removes it, so you can fix a slip without switching tools.
- Move freely: drag any piece to another square. In edit mode, moves do not have to be legal.
- Remove: drag a piece off the board, or choose the eraser and tap it.
- Start over: Clear board empties the board and selects the white king, the piece you need first. Start position resets to the opening setup.
- Undo steps back through edits and moves alike.
When you are done, press Play moves to leave edit mode. Copying a position square by square is quickest rank by rank: do White's pieces first, then Black's, then the pawns.
Side to move changes everything
The same arrangement of pieces can be winning for one side and level for the other, depending on whose move it is. The editor keeps White to move by default, so check this switch every time you copy a position where Black is to play.
With White to move, Stockfish finds 1.Re8#. Switch the side to move to Black and the evaluation drops to 0.00: Black simply makes an escape square with a pawn move such as ...g5 or ...f6, and the mate is gone. If you had analysed this position with the wrong side to move, you would have learned nothing about the game you were studying.
Castling rights
Castling is legal only if the king and that rook have never moved, so a board diagram alone cannot tell you whether it is still possible. The finder ticks a castling right automatically whenever the king and the matching rook stand on their original squares (king on e1 and rook on h1 for White's short castling, for example), and greys out rights that are impossible.
If the king or rook has moved away and come back during the game, untick the box. The engine treats castling as a resource; leaving a false right on can make it recommend a plan that would be illegal in the real game, or overestimate how safe the king is.
When you load a FEN that claims a right the position cannot have (for example "K" with no rook on h1), the finder removes it and tells you which right it dropped.
Reading FEN
FEN (Forsyth–Edwards Notation) describes a position in one line of text, which is why every analysis tool accepts it. Here is the position after 1.e4 c5 2.Nf3, the starting point of the Open Sicilian.
The FEN has six fields separated by spaces:
| Field | Value here | Meaning |
|---|---|---|
| Piece placement | rnbqkbnr/pp1ppppp/8/2p5/4P3/5N2/PPPP1PPP/RNBQKB1R | Ranks 8 down to 1, separated by "/". Capitals are White, lowercase Black; digits count empty squares. |
| Side to move | b | "w" or "b" |
| Castling | KQkq | Rights still available; "-" for none |
| En passant | - | The square a pawn passed over on the last move, if any |
| Halfmove clock | 1 | Moves since the last capture or pawn move (for the 50-move rule) |
| Fullmove number | 2 | Increases after each Black move |
Paste a FEN into the finder's FEN box and press Load or Enter. If you paste only the first four fields, the finder fills in the move counters. Copy puts the current position's FEN on your clipboard, ready for another tool or a note to yourself.
One detail trips people up: after a two-square pawn move, many tools write the en passant square even when no capture is possible. After 1.e4 the FEN is rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b KQkq e3 0 1. That "e3" is harmless; it only matters when an enemy pawn stands beside the pawn that moved.
Errors that make a position impossible
Engines search legal moves from a legal position. Give them something that could never occur and they may crash, return nonsense or refuse. The finder checks the position before every search and names the problem.
| Message type | What is wrong | Fix |
|---|---|---|
| No king / two kings | Each side needs exactly one king | Place or remove a king |
| Pawn on the first or last rank | A pawn on rank 1 or 8 is impossible: White pawns start on rank 2 and promote on rank 8, and the reverse for Black | Move it, or replace it with the piece it promoted to |
| Side not to move is in check | The player who just moved left their own king in check, which is illegal | Switch the side to move, or move the checking piece |
| Too many pieces or pawns | More than 16 pieces or 8 pawns for one side | Recount; a common slip is a duplicated pawn |
| Too many promoted pieces | For example a third knight while all eight pawns are still on the board | Each extra piece needs a missing pawn |
The "side not to move is in check" error usually means the side-to-move switch is wrong. Kings standing next to each other trigger it too, because each king would be attacking the other.
Positions that are legal but finished
Some positions are legal but leave nothing to search. If the side to move is checkmated or stalemated, the finder says so and keeps the Find button off. Two bare kings, or king and minor piece against king, are draws by insufficient material and are flagged the same way. If you are building a position piece by piece, this message disappears as soon as you add more material.
A setup checklist
Before you press Find the best move, run through this list. It takes twenty seconds and prevents most wrong answers.
- Count the pieces against your source, rank by rank.
- Check the side to move.
- Check each castling right against the game score: has the king or rook moved?
- If the last move was a two-square pawn push next to an enemy pawn, set the en passant square through the FEN.
- Flip the board if you are studying from Black's side, so the diagram matches your source.
Once the position is right, the method guide explains how to make your own choice before you ask the engine, and the practice positions give you ready-made FENs to try.
Fair play. Setting up positions is for study and finished games. Chess.com, Lichess, FIDE and US Chess forbid using an engine during a game against a person.