Server queries

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 up to 1400 bytes + IP/UDP headers. If a request or response needs more packets for the data it starts the packets with an additional header.
2023-07-10: Rust has been observed breaking this, sending packets up to the maximum IP size (64KB).
=== Simple Response Format ===
Data 	Type 	Comment
Header 	long 	Always equal to -1 (0xFFFFFFFF). Means it isn't split.
Payload	Payload	Payload
=== Multi-packet Response Format ===
====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 	Payload	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 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. AppIDs which are known not to contain this field: 215, 17550, 17700, and 240 when protocol = 7.	 	 	
This is only present in the first packet of the response and only if the response is being compressed.
{| style="margin:10px"	This is only present in the first packet of the response and only if the response is being compressed.
{| style="margin:10px"	This is only present in the first packet of the response and only if the response is being compressed.
{| style="margin:10px" 	Data	Type	Comment
Size 	long 	Size of the whole response once it is decompressed. 	 	 	
CRC32 sum	long 	CRC32 checksum of uncompressed response. 	 	 	
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).
Note: Some titles when using the split packet method have been observed erroneously nesting the single message header inside the split payload.
== Requests ==
The server responds to 5 queries:
;A2S_INFO
:Basic information about the server.
;A2S_PLAYER
:Details about each player on the server.
;A2S_RULES
:The rules the server is using.
;A2A_PING
:Ping the server. (DEPRECATED)
;A2S_SERVERQUERY_GETCHALLENGE
:Returns a challenge number for use in the player and rules query. (DEPRECATED)
Queries should be sent in UDP packets to the listen port of the server.
== Challenge Mechanism ==
Servers may respond with the data immediately. However, since this reply is larger than the request, it makes the server vulnerable to a reflection amplification attack.
Instead, the server may reply with a challenge to the client using S2C_CHALLENGE ('A' or 0x41). In that case, the client should repeat the request by appending the challenge number.
This change was introduced in December 2020 to address the reflection attack vulnerability, and all clients are encouraged to support the new protocol. See this post for more info.
Previously the structure of this document made it seem that only A2S_INFO messages would be responded with in this manner, however ANY of the queries made MAY result in a `S2C_CHALLENGE` response if either the challenge was omitted, is wrong, or has expired.
=== A2S_INFO ===
Retrieves information about the server including, but not limited to: its name, the map currently being played, and the number of players.
l4d2 server 2.2.1.3 update：some server will send challenge number ,it caused hlsw cant get server info;
==== Request Format ====
Data 	Type 	Value
Header 	byte 	'T' (0x54)
Payload 	string	"Source Engine Query\0"
Challenge	long 	4-byte challenge (sometimes -- see below)
 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.
Example for challenge number:
Server response:
FF FF FF FF 41 0A 08 5E EA
You need send :
FF FF FF FF 54 53 6F 75 72 63 65 20 45 6E 67 69 6E 65 20 51 75 65 72 79 00 0A 08 5E EA
NOTE: In the future, additional data may be appended to the request! Do not assume that if a request has extra data, that it is a bogus packet!
NOTE:changed 2021-6-19 13:05:43 :when l4d2 server received some packet from same ip address,it may deined replay
NOTE:some older titles have been observed sending the GoldSource INFO packet AND the newer INFO packet in reply to this.
==== Response Format ====
Data 	Type 	Comment 	 	 	
Header 	byte 	Always equal to 'I' (0x49) 	 	 	
Protocol 	byte 	Protocol version used by the server. 	 	 	
Name 	string	Name of the server. 	 	 	
Map 	string	Map the server has currently loaded. 	 	 	
Folder 	string	Name of the folder containing the game files. 	 	 	
Game 	string	Full name of the game. 	 	 	
ID 	short 	Steam Application ID of game. 	 	 	
Players 	byte 	Number of players on the server. 	 	 	
Max. Players	byte 	Maximum number of players the server reports it can hold. 	 	 	
Bots 	byte 	Number of bots on the server. 	 	 	
Server type 	byte 	Indicates the type of server: 'd' for a dedicated server'l' for a non-dedicated server'p' for a SourceTV relay (proxy) 	 	 	
Environment 	byte 	Indicates the operating system of the server: 'l' for Linux'w' for Windows'm' or 'o' for Mac (the code changed after L4D1)	 	 	
Visibility 	byte 	Indicates whether the server requires a password: 0 for public1 for private 	 	 	
VAC 	byte 	Specifies whether the server uses VAC: 0 for unsecured1 for secured 	 	 	
These fields only exist in a response if the server is running The Ship:
{| style="margin:10px;"	These fields only exist in a response if the server is running The Ship:
{| style="margin:10px;"	These fields only exist in a response if the server is running The Ship:
{| style="margin:10px;" 	Data	Type	Comment
Mode 	byte 	Indicates the game mode: 0 for Hunt1 for Elimination2 for Duel3 for Deathmatch4 for VIP Team5 for Team Elimination 	 	 	
Witnesses 	byte 	The number of witnesses necessary to have a player arrested. 	 	 	
Duration 	byte 	Time (in seconds) before a player is arrested while being witnessed. 	 	 	
Example response for Counter-Strike: Source:
 FF FF FF FF 49 02 67 61 6D 65 32 78 73 2E 63 6F ÿÿÿÿI.game2xs.co
 6D 20 43 6F 75 6E 74 65 72 2D 53 74 72 69 6B 65 m Counter-Strike
 20 53 6F 75 72 63 65 20 23 31 00 64 65 5F 64 75 Source #1.de_du
 73 74 00 63 73 74 72 69 6B 65 00 43 6F 75 6E 74 st.cstrike.Count
 65 72 2D 53 74 72 69 6B 65 3A 20 53 6F 75 72 63 er-Strike: Sourc
 65 00 F0 00 05 10 04 64 6C 00 00 31 2E 30 2E 30 e......dl..1.0.0
 2E 32 32 00 .22.
Example response for The Ship:
 FF FF FF FF 49 07 53 68 69 70 20 53 65 72 76 65 ÿÿÿÿI.Ship Serve
 72 00 62 61 74 61 76 69 65 72 00 73 68 69 70 00 r.batavier.ship.
 54 68 65 20 53 68 69 70 00 60 09 01 05 00 6C 77 The Ship.`....lw
 00 00 01 03 03 31 2E 30 2E 30 2E 34 00 .....1.0.0.4.
Example response for SiN 1 Multiplayer:
 FF FF FF FF 49 2F 53 65 6E 73 65 6D 61 6E 6E 20 ÿÿÿÿI/Sensemann 
 53 69 4E 20 44 4D 00 70 61 72 61 64 6F 78 00 53 SiN DM.paradox.S
 69 4E 20 31 00 53 69 4E 20 31 00 1D 05 00 10 00 iN 1.SiN 1......
 6C 77 00 00 31 2E 30 2E 30 2E 30 00 lw..1.0.0.0.
Example response for Rag Doll Kung Fu:
 FF FF FF FF 49 FC 54 68 65 20 44 75 64 65 27 73 ÿÿÿÿIüThe Dude's
 20 64 6F 6A 6F 00 53 6F 63 63 65 72 00 52 44 4B dojo.Soccer.RDK
 46 53 6F 63 63 65 72 00 52 61 67 44 6F 6C 6C 4B FSoccer.RagDollK
 75 6E 67 46 75 3A 20 53 6F 63 63 65 72 00 EA 03 ungFu: Soccer.ê.
 01 04 00 00 77 00 00 32 2E 33 2E 30 2E 30 00 ....w..2.3.0.0.
===== Obsolete GoldSource Response =====
GoldSource servers reply using the same response as Source servers. Older and pre-Steam servers still reply with the response format below. GoldSource can be distinguished from Source via AppIDs.
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	Map the server has currently 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 public1 for private 	 	 	
Mod 	byte 	Indicates whether the game is a mod: 0 for Half-Life1 for Half-Life mod 	 	 	
These fields are only present in the response if "Mod" is 1:
{| style="margin:10px"	These fields are only present in the response if "Mod" is 1:
{| style="margin:10px"	These fields are only present in the response if "Mod" is 1:
{| style="margin:10px" 	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 mod1 for multiplayer only mod 	 	 	
DLL 	byte 	Indicates whether mod uses its own DLL: 0 if it uses the Half-Life DLL1 if it uses its own DLL 	 	 	
Example response:
 FF FF FF FF 6D 37 37 2E 31 31 31 2E 31 39 34 2E ÿÿÿÿm77.111.194.
 31 31 30 3A 32 37 30 31 35 00 46 52 20 2D 20 56 110:27015.FR - V
 65 72 79 47 61 6D 65 73 2E 6E 65 74 20 2D 20 44 eryGames.net - D
 65 61 74 6D 61 74 63 68 20 2D 20 6F 6E 6C 79 20 eatmatch - only 
 73 75 72 66 5F 73 6B 69 20 2D 20 6E 67 52 00 73 surf_ski - ngR.s
 75 72 66 5F 73 6B 69 00 63 73 74 72 69 6B 65 00 urf_ski.cstrike.
 43 6F 75 6E 74 65 72 2D 53 74 72 69 6B 65 00 0C Counter-Strike..
 12 2F 64 6C 00 01 77 77 77 2E 63 6F 75 6E 74 65 ./dl..www.counte
 72 2D 73 74 72 69 6B 65 2E 6E 65 74 00 00 00 01 r-strike.net....
 00 00 00 00 9E F7 0A 00 01 01 00 ....ž÷.....
=== A2S_PLAYER ===
This query retrieves information about the players currently on the server. It needs an initial step to acquire a challenge number.
==== Request Format ====
Data 	Type	Value
Header 	byte	'U' (0x55)
Challenge	int 	Challenge number, or -1 (0xFFFFFFFF) to receive a challenge number.
Challenge response format:
Data 	Type	Value
Header 	byte	'A' (0x41)
Challenge	int 	Challenge number.
Example challenge request:
 FF FF FF FF 55 FF FF FF FF ÿÿÿÿUÿÿÿÿ"
Example challenge response:
 FF FF FF FF 41 4B A1 D5 22 ÿÿÿÿAÿÿÿÿ"
Example A2S_PLAYER request with the received challenge number:
 FF FF FF FF 55 4B A1 D5 22 ÿÿÿÿUÿÿÿÿ"
==== Response Format ====
Data 	Type 	Comment 	 	 	
Header 	byte 	Always equal to 'D' (0x44) 	 	 	
Players 	byte 	Number of players whose information was gathered. 	 	 	
For every player in "Players" there is this chunk in the response:
{| style="margin:10px"	For every player in "Players" there is this chunk in the response:
{| style="margin:10px"	For every player in "Players" there is this chunk in the response:
{| style="margin:10px"	Data	Type	Comment
Index 	byte 	Index of player chunk starting from 0. 	 	 	
Name 	string	Name of the player. 	 	 	
Score 	long 	Player's score (usually "frags" or "kills".) 	 	 	
Duration	float 	Time (in seconds) player has been connected to the server.	 	 	
The Ship additional player info (comes after the basic information in the packet):
Data 	Type	Comment
Deaths	long	Player's deaths
Money 	long	Player's money
Example response:
 FF FF FF FF 44 02 01 5B 44 5D 2D 2D 2D 2D 3E 54 ÿÿÿÿD..[D]---->T
 2E 4E 2E 57 3C 2D 2D 2D 2D 00 0E 00 00 00 B4 97 .N.W<----.....´—
 00 44 02 4B 69 6C 6C 65 72 20 21 21 21 00 05 00 .D.Killer !!!...
 00 00 69 24 D9 43 ..i$ÙC
The Ship response:
 FF FF FF FF 44 13 00 53 68 69 70 6D 61 74 65 31 ▒▒▒▒D..Shipmate1
 00 00 00 00 00 00 00 80 BF 01 53 68 69 70 6D 61 .......▒▒.Shipma
 74 65 32 00 00 00 00 00 00 00 80 BF 02 53 68 69 te2.......▒▒.Shi
 70 6D 61 74 65 33 00 00 00 00 00 00 00 80 BF 03 pmate3.......▒▒.
 53 68 69 70 6D 61 74 65 34 00 00 00 00 00 00 00 Shipmate4.......
 80 BF 04 53 68 69 70 6D 61 74 65 35 00 00 00 00 ▒▒.Shipmate5....
 00 00 00 80 BF 07 28 31 29 4C 61 6E 64 4C 75 62 ...▒▒.(1)LandLub
 62 65 72 00 00 00 00 00 D3 8E 68 45 00 00 00 00 ber.....ӎhE....
 C4 09 00 00 00 00 00 00 C4 09 00 00 00 00 00 00 ▒.......▒.......
 C4 09 00 00 00 00 00 00 C4 09 00 00 00 00 00 00 ▒.......▒.......
 C4 09 00 00 00 00 00 00 C4 09 00 00 ▒.......▒...
=== A2S_RULES ===
Returns the server rules, or configuration variables in name/value pairs. This query requires an initial challenge step.
The Console variables included are the ones marked with FCVAR_NOTIFY as well as any additional ones listed in the server configuration.
==== Request Format ====
Data 	Type	Value
Header 	byte	'V' (0x56)
Challenge	long	Challenge number, or -1 (0xFFFFFFFF) to receive a challenge number.
Challenge response format:
Data 	Type	Value
Header 	byte	'A' (0x41)
Challenge	long	Challenge number.
Example challenge request:
 FF FF FF FF 56 FF FF FF FF ÿÿÿÿVÿÿÿÿ"
Example challenge response:
 FF FF FF FF 41 4B A1 D5 22 ÿÿÿÿVK¡Õ"
Final request that includes the received challenge number:
 FF FF FF FF 56 4B A1 D5 22 ÿÿÿÿVK¡Õ"
==== Response Format ====
Data 	Type 	Comment 	 	 	
Header	byte 	Always equal to 'E' (0x45) 	 	 	
Rules 	short 	Number of rules in the response.	 	 	
For every rule in "Rules" there is this chunk in the response:
{| style="margin:10px;"	For every rule in "Rules" there is this chunk in the response:
{| style="margin:10px;"	For every rule in "Rules" there is this chunk in the response:
{| style="margin:10px;"	Data	Type	Comment
Name 	string	Name of the rule. 	 	 	
Value 	string	Value of the rule. 	 	 	
=== A2A_PING ===
Ping the server to see if it exists, this can be used to calculate the latency to the server.
==== 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_SERVERQUERY_GETCHALLENGE ===
A2S_PLAYER and A2S_RULES queries both require a challenge number. Formerly, this number could be obtained via an A2S_SERVERQUERY_GETCHALLENGE request. In newer games it no longer works. Instead, issue A2S_PLAYER or A2S_RULES queries with an initial challenge of -1 (0xFFFFFFFF) to receive a usable challenge number.
On some engines (confirmed AppIDs: 17510, 17530, 17740, 17550, 17700) it can be used. The format is:
==== Request Format ====
Data 	Type	Value
Header	byte	'W' (0x57)
 FF FF FF FF 57 ÿÿÿÿW
==== Response Format ====
Data 	Type	Comment
Header 	byte	Should be equal to 'A' (0x41.)
Challenge	long	The challenge number to use.
Example response:
 FF FF FF FF 41 4B A1 D5 22 ÿÿÿÿAK¡Õ"
== Implementations ==
* @fabricio-191/valve-server-query Server, Master Server and RCON protocols implementation for Node.js
* Steam Server Query Javascript (Node.js) module which implements the Master Server Query Protocol and Game Server Queries
* Asynchronous Game Query Library A Java 8 based Asynchronous Game Query Library powered by Netty
* Source Server Query Library C library
* libssq C library
* GameServer Java library
* QueryEd Java library
* Steam Condenser Java, PHP, and Ruby library
* GameDig Javascript (Node.JS) module
* Net-SRCDS-Queries Perl module
* a2squery Python library
* SRCDSpy Python library
* SourceLib Python library
* python-valve Python library
* Left4Query Python library
* valve-range-query Python Library for IP range query
* python-a2s Python library (supports async)
* dayzquery Add-on for python-a2s library which parses DayZ-specific binary data in A2S_RULES response
* SourceStats Source Server Statistics
* PHP Source Query PHP library
* SteamQuery.NET .NET/C# Wrapper (Built in .NET 8/.NET Standard 2.0, by cemahseri. Supports Source, GoldSource, and obsolete GoldSource protocols.)
* QueryMaster C# library
* QueryMaster C# library (remaster for .NET Standart 2.0)
* Okolni-Source-Query C# library (.NET Standard 2.0, Now Support l4d2 2213)
* A2S C# library utilizing NET5. (Currently supports A2S_Info and A2S_Player)
* aQuery VB.NET library
* go-a2s Golang library
* a2s-rs Rust library
* Rcon and A2s WebApi中文的WebApi协议库,基于Spring boot,仅支持A2S_INFO、A2S_PLAYER,Now Support l4d2 2213
* SteamPS Module that utilizes PowerShell as a wrapper for SteamCMD. Uses server queries in the command Get-SteamServerInfo
* Mirai Tencent QQ robot基于mriaiBot适配了a2s rcon的腾讯qq机器人,仅支持A2S_INFO、A2S_PLAYER,Rcon,Now Support l4d2 2213
* Rust-GameDig Rust library that supports the entirety of the protocol (also has the obsolete GoldSrc response).
* SteamQueryProxy Extremely high performance protocol proxy written in pure C for Linux (Can be used to mitigate VSE DoS attacks, supports Source & GoldSource).
* Steam2Go Golang library. Includes support for A2S, rcon and various WebAPI services.
== See also ==
* Master Server Query Protocol
* Source RCON Protocol
Category:Networking
Category:Technical
Category:Dedicated Server