stockfish

name	stockfish
description	Use this skill when the user asks to analyze a chess position, get the best move, evaluate a FEN string, check a chess move sequence, invokes /stockfish, asks "what should I play here?", "what's the best move?", or provides a FEN string and wants engine analysis. Use whenever there is a specific chess position to evaluate with an engine.
allowed-tools	Bash

Stockfish Chess Analysis

Analyze chess positions using the local Stockfish engine via UCI. Works with FEN strings or UCI move sequences.

Setup Check

Before first use, verify Stockfish is installed:

python3 ~/.claude/skills/stockfish/scripts/find_stockfish.py

If not found:

• macOS: brew install stockfish
• Linux: sudo apt install stockfish or sudo dnf install stockfish
• Override path: export STOCKFISH_PATH=/path/to/stockfish

Invocation

Always run analysis from the skill's scripts directory using absolute path:

python3 ~/.claude/skills/stockfish/scripts/analyze.py [OPTIONS]

From a Move Sequence

When the user provides moves in any order notation:

python3 ~/.claude/skills/stockfish/scripts/analyze.py \
  --mode multipv \
  --moves "e2e4 e7e5 g1f3 b8c6 f1b5" \
  --lines 3 \
  --depth 18

From a FEN String

python3 ~/.claude/skills/stockfish/scripts/analyze.py \
  --mode multipv \
  --fen "r1bqkbnr/pppp1ppp/2n5/1B2p3/4P3/5N2/PPPP1PPP/RNBQK2R b KQkq - 3 3" \
  --lines 3 \
  --depth 18

Best Move Only

python3 ~/.claude/skills/stockfish/scripts/analyze.py \
  --mode best-move \
  --fen "..." \
  --depth 20

Deep Analysis

python3 ~/.claude/skills/stockfish/scripts/analyze.py \
  --mode multipv \
  --fen "..." \
  --lines 5 \
  --depth 25

Time-Limited Analysis

python3 ~/.claude/skills/stockfish/scripts/analyze.py \
  --mode multipv \
  --fen "..." \
  --movetime 3000 \
  --lines 3

Options Reference

Option	Default	Description
--mode	multipv	best-move, multipv, or evaluate
--fen	—	FEN string (use instead of --moves)
--moves	""	UCI moves from startpos, space-separated
--depth	18	Search depth (12=fast, 18=good, 24+=deep)
--movetime	0	Search time in ms (overrides --depth if >0)
--lines	3	Top moves to show in multipv mode

Move Notation Translation

Users often give SAN notation. Translate to UCI long algebraic before passing to --moves:

SAN	UCI	Notes
e4	e2e4	Include source rank for pawns
Nf3	g1f3	Include full source square
O-O	e1g1	White kingside castle
O-O-O	e1c1	White queenside castle
o-o	e8g8	Black kingside castle
exd5	e4d5	Include source file+rank for captures
e8=Q	e7e8q	Append promotion piece letter

If the user provides a FEN, use --fen instead of translating moves.

Interpreting Output

• Score in pawns: +0.5 = slight White advantage, +2.0 = significant, +5.0 = decisive
• Negative scores favor Black
• "Mate in N": Stockfish sees forced checkmate in N moves
• Move notation: source+destination (e.g., e2e4, g1f3, e1g1 = kingside castle)

Default Depths

Use case	Depth	Typical time
Quick check	12	~0.3s
Normal analysis	18	~1–3s
Deep analysis	24	~5–15s
Maximum	30+	30s+

Reference Files

• references/uci-protocol.md — Full UCI command/response reference for debugging
• references/fen-notation.md — FEN format, common positions, SAN→UCI translation guide