Gunnar Farnebäck
July, 2002
Temporary comment: GNU Go 3.4 is currently under development and GTP version 2 has not yet been implemented in the development versions.
HT (dec 9) | Horizontal Tab |
CR (dec 13) | Carriage Return |
LF (dec 10) | Line Feed |
All other control characters must be discarded on input and should not be used on output.
SPACE (dec 32) | Space |
HT (dec 9) | Horizontal Tab |
In the rest of the specification we use 'space' to denote a whitespace character. On input this may be either a SPACE or a HT. On output only a SPACE should be used.
\n
to indicate a newline.
[id] command_name [arguments]
Here id is an optional identity number and command_name a string. The rest of the line (up to the first newline) gives the arguments of the command.
=[id] result
Here '=' indicates success, id is the identity number given in the command, and result is a piece of text ending with two consecutive newlines.
?[id] error_message
Here '?' indicates failure, id is the identity number given in the command, and error_message gives an explanation for the failure, also ending with two consecutive newlines.
In order to avoid this problem, standard commands do not include the dash (-) character. Private extensions are recommended to be of the form XXX-YYYYY, where XXX is a prefix which is sufficiently unique for the engine or controller in question, and YYYYY describes the command. E.g. a private variant of the genmove command used by GNU Go could be called gg-genmove.
Engines are allowed to use private extensions without a dash in the name, but then they do it at their own risk and must be prepared to change if the name later becomes used for a standard command.
When a command string arrives to an engine, it is expected to perform the following four operations before any further parsing takes place:
When a response arrives to a controller, it is expected only to do steps 1 and 3 above.
Naturally an implementation does not have to actually do this preprocessing as a separate step but may interleave it with other parts of the parsing. For purposes of the following specifications, though, the preprocessing is supposed to have been carried out in full.
id command_name arguments\n id command_name\n command_name arguments\n command_name\n
=id response\n\n =id\n\n = response\n\n =\n\n
?id error_message\n\n ? error_message\n\n
The protocol supports both fixed placement of handicap stones and free placement. The handicap stones are always black.
With fixed placement the handicap stones are set in predetermined positions. The maximum number of fixed handicap stones varies with the board size but is never larger than 9. On a 19x19 board, the positions for the handicap stones are given by this table:
Handicap | Vertices |
2 | D4 Q16 |
3 | D4 Q16 D16 |
4 | D4 Q16 D16 Q4 |
5 | D4 Q16 D16 Q4 K10 |
6 | D4 Q16 D16 Q4 D10 Q10 |
7 | D4 Q16 D16 Q4 D10 Q10 K10 |
8 | D4 Q16 D16 Q4 D10 Q10 K4 K16 |
9 | D4 Q16 D16 Q4 D10 Q10 K4 K16 K10 |
The placement of handicap stones on other board sizes mirrors that of 19x19 with stones at a specific distance from the edges and on the middle lines of the board, with the following caveats:
More explicitly we obtain the following table:
board size | max handicap | edge distance |
25 | 9 | 4 |
24 | 4 | 4 |
23 | 9 | 4 |
22 | 4 | 4 |
21 | 9 | 4 |
20 | 4 | 4 |
19 | 9 | 4 |
18 | 4 | 4 |
17 | 9 | 4 |
16 | 4 | 4 |
15 | 9 | 4 |
14 | 4 | 4 |
13 | 9 | 4 |
12 | 4 | 3 |
11 | 9 | 3 |
10 | 4 | 3 |
9 | 9 | 3 |
8 | 4 | 3 |
7 | 4 | 3 |
6 | - | - |
5 | - | - |
4 | - | - |
3 | - | - |
2 | - | - |
With free placement the handicap stones are set as chosen by the
controller or by one of the engines (for normal tournament use the
engine playing the black stones would make the choice). The smallest
number of handicap stones is 2. The maximum number requires some
discussion. Let the board size be and thus the number of vertices
.
The theoretical upper limit for the number of handicap stones is ,
but since this would leave all stones in atari, black is clearly better
off with fewer stones. In fact, for sufficiently large (but smaller than
) handicaps, black can arrange the stones so that white cannot
possibly form a single living group even if black passes for the entire
game. In particular, with
stones, black can trivially place the
stones in a chessboard pattern so that white does not have a single
legal move.
With this in mind, we do allow up to handicap stones. However,
an engine asked to choose placement of handicap stones is allowed to
place a smaller number of stones than the one requested, if this is
larger than some threshold. To be more precise, let
be the
threshold and
the requested number of handicap stones. If
,
the engine must place
handicap stones and if
, the engine
must place
handicap stones. The value of
is determined by the
engine and may vary with the board size. It is recommended that every
engine has a threshold of at least 40 for 19x19, unless it is totally
convinced that there is some smaller number for which it cannot
possibly lose against any opponent.
The protocol has support for Canadian byo yomi, including absolute time (no byo yomi) as a special case. Canadian byo yomi is characterized by the three parameters
Setting means that the engine immediately starts in byo yomi.
Setting
means that if the main time is up before the game is
over, the engine loses on time. Setting
and
means no time
limits.
An engine is expected to keep track of the following state information:
There is no default state for any state variable. When first started, the engine may set these as it likes. A controller which has some specific opinion about these values must set them explicitly with the appropriate commands, including clearing the board.
The state is changed by certain commands, as specified in their description in section 6. State which is not explicitly modified must remain unchanged. A failed command must never change any state.
protocol_version name version known_command list_commands quit boardsize clear_board komi play genmove
fixed_handicap, place_free_handicap, set_free_handicap
loadsgf, reg_genmove
arguments | none |
effects | none |
output | version_number |
int version_number - Version of the GTP Protocol | |
fails | never |
comments | For this specification 2. |
arguments | none |
effects | none |
output | name |
string* name - Name of the engine | |
fails | never |
comments | E.g. ``GNU Go'', ``GoLois'', ``Many Faces of Go''. The name does not include any version information, which is provided by the version command. |
arguments | none |
effects | none |
output | version |
string* version - Version of the engine | |
fails | never |
comments | E.g. ``3.1.33'', ``10.5''. Engines without a sense of version number should return the empty string. |
arguments | command_name |
string command_name - Name of a command | |
effects | none |
output | known |
boolean known - ``true'' if the command is known by the engine, ``false'' otherwise | |
fails | never |
comments | The protocol makes no distinction between unknown commands and known but unimplemented ones. Do not declare a command as known if it is known not to work. |
arguments | none |
effects | none |
output | commands |
string& commands - List of commands, one per row | |
fails | never |
comments | Include all known commands, including required ones and private extensions. |
arguments | none |
effects | The session is terminated and the connection is closed. |
output | none |
fails | never |
comments | The full response of this command must be sent before the engine closes the connection. The controller must receive the response before the connection is closed on its side. |
arguments | size |
int size - New size of the board. | |
effects | The board size is changed. The board configuration, number of captured, and move history become arbitrary. |
output | none |
fails | If the engine cannot handle the new size, fails with the error message "unacceptable size". |
comments | In GTP version 1 this command also did the work of clear_board. This may or may not be true for implementations of GTP version 2. Thus the controller must call clear_board explicitly. Even if the new board size is the same as the old one, the board configuration becomes arbitrary. |
arguments | none |
effects | The board is cleared, the number of captured stones is reset to zero for both colors and the move history is reset to empty. |
output | none |
fails | never |
comments |
arguments | new_komi |
float new_komi - New value of komi. | |
effects | Komi is changed. |
output | none |
fails | syntax error |
comments | The engine must accept the komi even if it should be ridiculous. |
arguments | number_of_stones |
int number_of_stones - Number of handicap stones. | |
effects | Handicap stones are placed on the board according to the specification in section 4.1.1. |
output | vertices |
vertex* vertices - A list of the vertices where handicap stones have been placed. | |
fails | syntax error, invalid number of stones, board not empty |
comments | This command is only valid if the board is empty. See section 4.1.1 for valid number of handicap stones. The handicap stones are not included in the move history. |
arguments | number_of_stones |
int number_of_stones - Number of handicap stones. | |
effects | Handicap stones are placed on the board on the vertices the engine prefers. See also section 4.1.2. |
output | vertices |
vertex* vertices - A list of the vertices where handicap stones have been placed. | |
fails | syntax error, invalid number of stones, board not empty |
comments | This command is only valid if the board is empty. The engine may place fewer than the requested number of stones on the board under certain circumstances, as discussed in section 4.1.2. The controller can check this by counting the number of vertices in the response. The handicap stones are not included in the move history. |
arguments | vertices |
vertex* vertices - A list of vertices where handicap stones should be placed on the board. | |
effects | Handicap stones are placed on the vertices as requested. |
output | none |
fails | syntax error, board not empty |
comments | This command is only valid if the board is empty. The list must have at least two elements and no more than the number of board vertices minus one. The engine must accept the handicap placement. The handicap stones are not included in the move history. |
arguments | move |
move move - Color and vertex of the move | |
effects | A stone of the requested color is played at the requested vertex. The number of captured stones is updated if needed and the move is added to the move history. |
output | none |
fails | syntax error, illegal move |
comments |
arguments | color |
color color - Color for which to generate a move. | |
effects | A stone of the requested color is played where the engine chooses. The number of captured stones is updated if needed and the move is added to the move history. |
output | vertex |
vertex![]() |
|
fails | never |
comments |
arguments | none |
effects | The board configuration and the number of captured stones are reset to the state before the last move. The last move is removed from the move history. |
output | none |
fails | If the engine is unable to take back the last move, fails with the error message "unable to undo". |
comments | If you want to take back multiple moves, use this command multiple times. The engine may fail to undo if the move history is empty or if the engine only maintains a partial move history, which has been exhausted by previous undos. It is never possible to undo handicap placements. Use clear_board if you want to start over. An engine which never is able to undo should not include this command among its known commands. |
arguments | main_time byo_yomi_time byo_yomi_stones |
int main_time - Main time measured in seconds. | |
int byo_yomi_time - Byo yomi time measured in seconds. | |
int byo_yomi_stones - Number of stones per byo yomi period. | |
effects | The time settings are changed. |
output | none |
fails | syntax error |
comments | The interpretation of the parameters is discussed in section 4.2. The engine must accept the requested values. This command gives no provision for negotiation of the time settings. |
arguments | color time stones |
color color - Color for which the information applies. | |
int time - Number of seconds remaining. | |
int stones - Number of stones remaining. | |
effects | none |
output | none |
fails | syntax error |
comments | While the main time is counting, the number of remaining stones is given as 0. |
arguments | |
effects | |
output | |
fails | |
comments |
arguments | |
effects | |
output | |
fails | |
comments |
arguments | |
effects | |
output | |
fails | |
comments |
arguments | |
effects | |
output | |
fails | |
comments |
arguments | |
effects | |
output | |
fails | |
comments |
arguments | |
effects | |
output | |
fails | |
comments |
The protocol is not intended as a user interface for playing games though, even if it can be done for testing purposes.
Arguably an engine could fail on purpose as some kind of attempt to force negotiation. This is not encouraged and is considered bad style. A controller has absolutely no obligation to try to work around such failures.
This coordinate convention is identical to the one used on IGS and many other go servers, as well as by the Go Modem Protocol.
For similar reasons constructions of the form {x& y&} or x&* are also invalid.
The multiline list construction cannot be used for commands since these are terminated by a single LF.
In constructions of the form x*&, there is no requirement that every x* has the same length. I.e., there may be varying number of elements on each line.
The reason for a separate reg_genmove command is that it is usually desirable to get consistent regression results. I.e. for a given position the same move should always be generated. In actual play it is useful to have a random variability between moves of similar value, in particular in the opening, to avoid playing too predictably.
The reason why this is considered complex is that there are numerous rulesets (using the term loosely) such as Japanese, Chinese, AGA, Ing, IGS, and New Zealand, which differ with respect to one or more of ko rule, area or territory scoring, scoring of seki, legality of suicide, effect of handicap stones on scoring, and so on.
As a workaround this kind of information has to be passed through other channels than GTP, e.g. as command line options when starting the engine.
In practice this is not all that much of a problem since these settings rarely vary between games, e.g. within a tournament. Still it is desirable to have this functionality in the protocol, but it is worth waiting for a well thought through design of the commands.
This document may be copied, modified, and distributed according to the terms of the GNU Free Documentation License, included in section 10.
While this in theory allows anyone to create modified protocol specifications, which could potentially lead to great chaos, that would benefit noone and we trust people not be that stupid.
The reason why we allow modification at all is to make sure that new authors can continue evolving the protocol if previous authors disappear, without having to rewrite everything from scratch.
People who want to use this protocol as a basis for development of some other protocol are most welcome to start from this protocol specification.
Version 1.1, March 2000
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