Server queries

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You can query information from a running game server using UDP/IP packets. This document describes the packet formats and protocol to access this data.

Data Types

All server queries consist of five basic types of data packed together into a data stream. All types are little endian, which is the default on most languages on x86 CPUs. Java users should use ByteBuffer to convert.

Name	Description
byte	8 bit character or unsigned integer
short	16 bit signed integer
long	32 bit signed integer
float	32 bit floating point
long long	64 bit unsigned integer
string	variable-length byte field, encoded in UTF-8, terminated by 0x00

Protocol

Steam uses a packet size of 1400 bytes + IP/UDP headers. If a request or response needs more packets for the data it starts the packets with an additional header.

Simple Response

Data	Type	Comment
Header	long	Always equal to -1 (0xFFFFFFFF). Means it isn't split.
Payload

Multi-packet Response

Goldsource Server

Data	Type	Comment
Header	long	Always equal to -2 (0xFFFFFFFE). Means the packet is split.
ID	long	Unique number assigned by server per answer.
Packet number	byte	Upper 4 bits represent the number of the current packet (starting at 0) and bottom 4 bits represent the total number of packets (2 to 15).
Payload

Source Server

Data	Type	Comment
Header	long	Always equal to -2 (0xFFFFFFFE). Means the packet is split.
ID	long	Same as the Goldsource server meaning. However, if the  most significant bit is 1, then the response was compressed with bzip2 before being cut and sent. Refer to compression procedure below.
Total	byte	The total number of packets in the response.
Number	byte	The number of the packet. Starts at 0.
Size	short	(Orange Box Engine and above only.) Maximum size of packet before packet switching occurs. The default value is 1248 bytes (0x04E0), but the server administrator can decrease this. For older engine versions: the maximum and minimum size of the packet was unchangeable.
This is only present in the first packet of the response and only if the response is being compressed. Data Type Comment Size long Size of the whole response once it is decompressed. CRC32 sum long CRC32 checksum of uncompressed response. To uncompress this response: collect and assemble all the packets of the answer, then pass that into a function like BZ2_bzBuffToBuffDecompress() in C, bzdecompress() in PHP, or bz2.decompress() in Python.
Payload

Because UDP packets can arrive in different order or delayed, every packet should be verified by its "ID" and "Number"! Every request or response with or without this header is continued with an integer -1 (0xFFFFFFFF) and the user data. So by reading the first 4 bytes you can decide whether the data is split (-2) or in one packet (-1).

Warning:TF2 currently does not split replies, expect A2S_PLAYER and A2S_RULES to be simply cut off after 1260 bytes.

Requests

The server responds to 5 queries:

A2A_PING

Ping the server.

A2S_SERVERQUERY_GETCHALLENGE

Returns a challenge number for use in the player and rules query.

A2S_INFO

Basic information about the server.

A2S_PLAYER

Details about each player on the server.

A2S_RULES

The rules the server is using.

Queries should be sent in UDP packets to the listen port of the server.

A2A_PING

Ping the server to see if it exists, this can be used to calculate the latency to the server.

Warning:According to an official, Valve mailing list posted on the Talk Page, A2A_PING is no longer supported on Counter Strike: Source and Team Fortress 2 servers at this time, and is considered a deprecated feature.

Request format

Data	Type	Value
Header	byte	'i' (0x69)

FF FF FF FF 69 ÿÿÿÿi

Response format

Goldsource Server

Data	Type	Value
Header	byte	'j' (0x6A)
Payload	string	Null

FF FF FF FF 6A 00 ÿÿÿÿj.

Source Server

Data	Type	Value
Heading	byte	'j' (0x6A)
Payload	string	'00000000000000'

FF FF FF FF 6A 30 30 30 30 30 30 30 30 30 30 30 ÿÿÿÿj00000000000 30 30 30 00 000.

A2S_INFO

Retrieves information about the server including, but not limited to: its name, the map currently being played, and the number of players.

Request format

Data	Type	Value
Header	byte	'T' (0x54)
Payload	string	"Source Engine Query"

FF FF FF FF 54 53 6F 75 72 63 65 20 45 6E 67 69 ÿÿÿÿTSource Engi 6E 65 20 51 75 65 72 79 00 ne Query

Response format

Goldsource servers

Warning:This is obsolete. GoldSource servers (except for HLTV ones?) now report using the same protocol as Source servers. To differentiate between (for example) Counter-Strike and Counter-Strike: Source, or other games with the same gamedir, use the Steam AppId.

Data	Type	Comment
Header	byte	Always equal to 'm' (0x6D.)
Address	string	IP address and port of the server.
Name	string	Name of the server.
Map	string	Current map the server has loaded.
Folder	string	Name of the folder containing the game files.
Game	string	Full name of the game.
Players	byte	Number of players on the server.
Max. Players	byte	Maximum number of players the server reports it can hold.
Protocol	byte	Protocol version used by the server.
Server type	byte	Indicates the type of server: 'D' for dedicated server 'L' for non-dedicated server 'P' for a HLTV server
Environment	byte	Indicates the operating system of the server: 'L' for Linux 'W' for Windows
Visibility	byte	Indicates whether the server requires a password: 0 for public 1 for private
Mod	byte	Indicates whether the game is a mod: 0 for Half-Life 1 for Half-Life mod
These fields are only present in the response if "Mod" is 1: Data Type Comment Link string URL to mod website. Download Link string URL to download the mod. NULL byte NULL byte (0x00) Version long Version of mod installed on server. Size long Space (in bytes) the mod takes up. Type byte Indicates the type of mod: 0 for single and multiplayer mod 1 for multiplayer only mod DLL byte Indicates whether mod uses its own DLL: 0 if it uses the Half-Life DLL 1 if it uses its own DLL
VAC	byte	Specifies whether the server uses VAC: 0 for unsecured 1 for secured
Bots	byte	Number of bots on the server.

Note:HLTV servers may respond with a late request that is either incomplete or incorrect if the number of slots is 255.

A2S_SERVERQUERY_GETCHALLENGE

Request format

Challenge values are required for A2S_PLAYER and A2S_RULES requests, you can use this request to get one.

Note:You can also send A2S_PLAYER and A2S_RULES queries with a challenge value of -1 (0xFF FF FF FF) and they will respond with a challenge value to use (using the response format below).

Warning:As of September 29, 2009, the implementation of this query does not function in Goldsource nor Left4Dead2 servers. Use the method described above as a workaround. For more, see the Talk Page

FF FF FF FF 57

Response format

Data	Type	Comment
Type	byte	Should be equal to 'A' (0x41)
Challenge	long	The challenge number to use

Example response:

FF FF FF FF 41 32 42 59 45

A2S_PLAYER

Request format

FF FF FF FF 55 <4 byte challenge number>

The challenge number can either be set to -1 (0xFF FF FF FF) to have the server response with S2C_CHALLENGE, or use the value from a previous A2S_SERVERQUERY_GETCHALLENGE request.

Response format

The players response has two sections, the initial header:

Data	Type	Comment
Type	byte	Should be equal to 'D' (0x44)
Num Players	byte	The number of players reported in this response

Then for each player the following fields are sent:

Data	Type	Comment
Index	byte	The index into [0.. Num Players] for this entry
Player Name	string	Player's name
Kills	long	Number of kills this player has
Time connected	float	The time in seconds this player has been connected

Note: Java users can read the player score as an int and reverse the bytes with Integer.reverseBytes(int i).

Warning:As of September 29, 2009, Left4Dead2 returns an index of zero for all players.

A2S_RULES

Request format

FF FF FF FF 56 <4 byte challenge number>

The challenge number can either be set to -1 (0xFF FF FF FF) to have the server reply with S2C_CHALLENGE, or use the value from a previous A2S_SERVERQUERY_GETCHALLENGE request.

Response format

The rules response has two sections, the initial header:

Data	Type	Comment
Type	byte	Should be equal to 'E' (0x45)
Num Rules	short	The number of rules reported in this response

Then for each rule the following fields are sent:

Data	Type	Comment
Rule Name	string	The name of the rule
Rule Value	string	The rule's value

Implementations

• Source Server Query Library C library
• GameServer Java library
• QueryEd Java library
• Steam Condenser Java, PHP, and Ruby library
• Net-SRCDS-Queries Perl module
• SRCDSpy Python library
• SourceLib Python library
• aQuery VB.NET library
• SourceStats Source Server Statistics
• PHP Source Query PHP library

See Also

• Master Server Query Protocol
• Source RCON Protocol