Skip to content

fen_notation.md

Latest commit

 

History

History
94 lines (64 loc) · 1.82 KB

fen_notation.md

File metadata and controls

94 lines (64 loc) · 1.82 KB

🧩 Structure of FEN

A FEN string looks like this:

rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1

It contains 6 space-separated fields:

  1. Piece placement
  2. Active color
  3. Castling availability
  4. En passant target square
  5. Halfmove clock
  6. Fullmove number

📘 1. Piece placement

This part represents the board layout, starting from rank 8 to rank 1 (top to bottom), with / separating ranks.

Pieces are represented by letters:

  • Uppercase = White (P, N, B, R, Q, K)
  • Lowercase = Black (p, n, b, r, q, k)
  • Digits = number of empty squares

Example:

rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR

This is the initial board setup.

⚪ 2. Active color

Whose turn it is:

  • w = White
  • b = Black

♔ 3. Castling availability

  • Letters indicate castling rights:
    • K = White kingside
    • Q = White queenside
    • k = Black kingside
    • q = Black queenside
  • - if no castling is available

Example:

KQkq

Means both players can castle both ways.

🏹 4. En passant target square

If a pawn has just moved two squares forward, this shows the square behind it for en passant.

  • Example: e3 (white just moved pawn from e2 to e4, black can capture en passant on e3)
  • - means no en passant possible

⏱ 5. Halfmove clock

Number of halfmoves since the last pawn move or capture. Used for the 50-move draw rule.

🔢 6. Fullmove number

Starts at 1, and increments after Black's move.

🔍 Full example explained

rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1
  • Position: Starting position
  • White to move
  • Both sides can castle both directions
  • No en passant
  • 0 halfmoves since capture/pawn move
  • Move number 1