Droppable Reserve Operations Placement (DROP) Specification

Version: 1.0.0
Author: Sashité
Published: June 17, 2025
License: MIT License

Overview

DROP defines a simple, standardized notation for piece reserve locations in board games where captured pieces can be held and/or placed onto the board. This applies to games like shōgi, crazyhouse, go, and other games featuring capture-and-drop mechanics.

Format

DROP uses a single character to represent all off-board reserve locations:

Reserve Location: * (asterisk)

Unicode: U+002A
ASCII: 42
UTF-8: 0x2A

Validation

\A\*\z

Usage Examples

Movement Notation

* → e4    Place piece from reserve to board position e4
e4 → *    Capture piece at e4 to reserve
e2 → e4   Regular on-board movement (using CELL coordinates)

Game Context Examples

Shōgi

Reserve: *
Board: a1 to i9 (CELL coordinates)
Drop move: * → e5 (place piece from reserve)

Crazyhouse

Reserve: *
Board: a1 to h8 (CELL coordinates)
Drop move: * → e4 (place captured piece)

Integration with CELL

DROP complements the CELL specification to provide complete location coverage:

On-board positions: CELL coordinates (a1, e4, a1A, etc.)
Off-board reserve: DROP location (*)

Combined grammar:

<location> ::= <cell> | <drop>
<drop>     ::= "*"

Design Rationale

Why the asterisk?

Universal keyboard availability
High visual contrast with CELL coordinates
Commonly used as a “wildcard” symbol
Single character keeps notation concise

Simplicity by design

DROP intentionally uses just one character because reserve locations don’t need dimensional complexity—context determines meaning (player’s reserve, captured pieces, stone supply, etc.).

Relationship to Other Notations

Notation	Purpose	Relationship to DROP
CELL	Multi-dimensional board coordinates	DROP complements CELL by providing `"*"` notation for off-board reserve locations
MIN	Concise move identification	Uses DROP location for source/destination in drop and capture moves
PMN	Mechanical move decomposition	Uses DROP location for reserve-related actions in move sequences

Reference Implementations

This section lists available libraries and tools that implement the DROP specification.

Ruby

Drop.rb - Reference implementation