Numeric Annotation Glyphs

Portable Game Notation (PGN) is a standard plain text format for recording chess games (both the moves and related data), which can be read by humans and is also supported by most chess software.

History

PGN was devised around 1993, by Steven J. Edwards, and was first popularized and specified via the Usenet newsgroup rec.games.chess.

Usage

PGN is structured "for easy reading and writing by human users and for easy parsing and generation by computer programs." The chess moves themselves are given in algebraic chess notation using English initials for the pieces. The filename extension is .pgn.

There are two formats in the PGN specification, the "import" format and the "export" format. The import format describes data that may have been prepared by hand, and is intentionally lax; a program that can read PGN data should be able to handle the somewhat lax import format. The export format is rather strict and describes data prepared under program control, similar to a pretty printed source program reformatted by a compiler. The export format representations generated by different programs on the same computer should be exactly equivalent, byte for byte.

PGN text begins with a set of "tag pairs" (a tag name and its value), followed by the "movetext" (chess moves with optional commentary).

Tag pairs

Tag pairs begin with an initial left bracket , followed by the name of the tag in plain ASCII text. The tag value is enclosed in double-quotes, and the tag is then terminated with a closing right bracket . A quote inside a tag value is represented by the backslash immediately followed by a quote. A backslash inside a tag value is represented by two adjacent backslashes. There are no special control codes involving escape characters, or carriage returns, and linefeeds to separate the fields, and superfluous embedded spaces are usually skipped when parsing.

Seven Tag Roster

PGN data for archival storage is required to provide seven tag pairs – together known as the "''Seven Tag Roster''". In export format, these tag pairs must appear before any other tag pairs and in this order:

Optional tag pairs

The standard allows for other optional tag pairs. The more common ones include:

Movetext

Chessboard notation, frame

The movetext describes the actual moves of the game. This includes move number indicators (numbers followed by either one or three periods; one if the next move is White's move, three if the next move is Black's move) and movetext in Standard Algebraic Notation (SAN).

For most moves the SAN consists of the letter abbreviation for the piece, an x if there is a capture, and the two-character algebraic name of the final square the piece moved to. The letter abbreviations are K (king), Q (queen), R (rook), B (bishop), and N (knight). The pawn is given an empty abbreviation in SAN movetext, but in other contexts the abbreviation P is used. The algebraic name of any square is as per usual algebraic chess notation; from white's perspective, the leftmost square closest to white is a1, the rightmost square closest to the white is h1, and the rightmost (from white's perspective) square closest to black side is h8.

In a few cases, a more detailed representation is needed to resolve ambiguity; if so, the piece's file letter, numerical rank, or the exact square is inserted after the moving piece's name (in that order of preference). Thus, Nge2 specifies that the knight originally on the g-file moves to e2.

SAN kingside castling is indicated by the sequence O-O; queenside castling is indicated by the sequence O-O-O (note that these are capital Os, not zeroes, contrary to the FIDE standard for notation). Pawn promotions are notated by appending = to the destination square, followed by the piece the pawn is promoted to. For example: e8=Q. If the move is a checking move,
+ is also appended; if the move is a checkmating move, # is appended instead. For example: e8=Q#.

An annotator who wishes to suggest alternative moves to those actually played in the game may insert variations enclosed in parentheses. They may also comment on the game by inserting Numeric Annotation Glyphs (NAGs) into the movetext. Each NAG reflects a subjective impression of the move preceding the NAG or of the resultant position.

If the game result is anything other than *, the result is repeated at the end of the movetext.

Comments

Comments are inserted by either a ; (a comment that continues to the end of the line) or a ). Comments do not nest.

Example

Here is the PGN format of the 29th game of the 1992 match played in Yugoslavia between Bobby Fischer and Boris Spassky:

Handling chess variants

Many chess variants can be recorded using PGN, provided the names of the pieces can be limited to one character, usually a letter and not a number. They are typically noted with a tag named "Variant" giving the name of the rules. The term "Variation" must be avoided, as that refers to the name of an opening variation. Note that traditional chess programs can only handle, at most, a few variants. Forsyth-Edwards Notation is used to record the starting position for variants (such as Chess960) which have initial positions other than the orthodox chess initial position.

Numeric Annotation Glyphs

Numeric Annotation Glyphs or NAGs are used to annotate chess games when using a computer, typically providing an assessment of a chess move or a chess position. NAGs exist to indicate a simple annotation in a language independent manner.
NAGs were first formally documented in 1994 by Steven J. Edwards in his "Portable Game Notation Specification and Implementation Guide". Within the PGN specification, 256 NAGs are proposed of which the first 140 are defined; the remainder were reserved for future definition.

A Numeric Annotation Glyph is composed of a dollar sign character ("$") immediately followed by one or more digit characters. Each NAG then has a specific meaning and often a standard typographical representation. The meanings first defined stemmed from the use of specific typographic symbols when annotators were commenting upon chess games; most especially in Chess Informant ''Uses FigurineCB webfont.'' publications. The objective was to devise an alternative representation of these symbols which could be incorporated in the simple computer file format proposed as the PGN standard. This mechanism allowed often sophisticated typography to be expressed using the simple ASCII character set.

Since its inception there has been no attempt to further formalise or standardise the meaning of the undefined 116 NAGs although PGN editors, such as ChessPad, have variously used these higher glyphs.

Standard NAGs

Non-standard NAGs

Notes on tables

# Some of the symbols are not rendered by some browsers
# The more exotic symbols used by Chess Informator are often derived from common mathematical typographic symbols; their mathematical meaning rarely has any relevance to their chess meaning
# The entries in the Unicode column are, respectively, the decimal and hexadecimal reference for the character or symbol
# The entries in the HTML column are named HTML entities for representing the symbol or character; the Unicode numeric value can always be used where a specific entity does not exist. For example, the ''left right double arrow'' ($239) can be represented as either Unicode decimal ⇔ (⇔) or Unicode hexadecimal ⇔ (⇔) or HTML ⇔ (⇔). Unless explicitly noted, the Unicode representation can be interpreted as a default.

See also

* Forsyth–Edwards Notation
* X-FEN
* Smart Game Format – Format for recording Go games
* Portable Draughts Notation

Notes

References

Sources

* Krogius, N; Livsic, A; Parma, B; Tajmanov, M. ''Encyclopedia of Chess Middlegames''. (1980) Belgrade: Chess Informant.
* Malanovic, Aleksander (Editor) ''Encyclopedia of Chess Openings, volumes A-E''. (1978) Belgrade: Chess Informant.

{{Chess

Chess notation
Computer file formats
1993 introductions