Master Server Query Protocol

This page documents the legacy Steam master server query protocol. The legacy master is still used by older games and mods, but all current games and mods query the master server through Steam directly.
== Client to master server ==
Send the following UDP query to a master server to get a list of Source host servers.
=== Format ===
Type 	Field 	Value
Byte 	Message Type	0x31 - the character "1"
Byte 	Region Code 	See below
String Zero	IP:Port 	See below
String Zero	Filter 	See below
==== Region codes ====
The region of the world that you wish to find servers in.
Byte	Description
0x00	US East coast
0x01	US West coast
0x02	South America
0x03	Europe
0x04	Asia
0x05	Australia
0x06	Middle East
0x07	Africa
0xFF	Rest of the world
==== IP:Port ====
The first IP:Port you should send is "0.0.0.0:0"
From then on, IP:Port becomes the last IP:Port received in the master servers reply. This allows steam to then grab another list of more servers.
Terminate this with 0x00
Note that whenever you open a new socket (and thus get a new random client port), the Master Server will always send you the first batch of IPs even if you pass a valid game server IP. Do not close your socket between packets.
==== Filter ====
Allows you to restrict the results to servers running a certain game, map, etc.
Insert \ in between filter parameters
Filter code 	What the filter returns
0x00 (NULL, empty string)	All servers
\nor\[x] 	A special filter, specifies that servers matching any of the following [x] conditions should not be returned
\nand\[x] 	A special filter, specifies that servers matching all of the following [x] conditions should not be returned
\dedicated\1 	Servers running dedicated
\secure\1 	Servers using anti-cheat technology (VAC, but potentially others as well)
\gamedir\[mod] 	Servers running the specified modification (ex. cstrike)
\map\[map] 	Servers running the specified map (ex. cs_italy)
\linux\1 	Servers running on a Linux platform
\password\0 	Servers that are not password protected
\empty\1 	Servers that are not empty
\full\1 	Servers that are not full
\proxy\1 	Servers that are spectator proxies
\appid\[appid] 	Servers that are running game [appid]
\napp\[appid] 	Servers that are NOT running game [appid] (This was introduced to block Left 4 Dead games from the Steam Server Browser)
\noplayers\1 	Servers that are empty
\white\1 	Servers that are whitelisted
\gametype\[tag,...] 	Servers with all of the given tag(s) in sv_tags
\gamedata\[tag,...] 	Servers with all of the given tag(s) in their 'hidden' tags (L4D2)
\gamedataor\[tag,...] 	Servers with any of the given tag(s) in their 'hidden' tags (L4D2)
\name_match\[hostname] 	Servers with their hostname matching [hostname] (can use * as a wildcard)
\version_match\[version] 	Servers running version [version] (can use * as a wildcard)
\collapse_addr_hash\1 	Return only one server for each unique IP address matched
\gameaddr\[ip] 	Return only servers on the specified IP address (port supported and optional)
=== Sample query ===
To get all servers everywhere:
0000 31 FF 30 2E 30 2E 30 2E 1.0.0.0.
0008 30 3A 30 00 00 0:0..
This is the default Steam Server Browser query to the Source Master Server. It uses the napp filter to filter out Left 4 Dead games (which are meant to be joined using the matchmaking feature).
 
 31 ff 30 2e 30 2e 30 2e 30 3a 30 00 5c 6e 61 70 1.0.0.0.0:0.\nap
 70 5c 35 30 30 00 p\500.
=== Master servers ===
Current master servers are:
;GoldSrc
:Currently hl1master.steampowered.com and MasterServer2.vdf contain the old outdated IPs for querying HL1 master servers (although heartbeat may work). The new IPs (for querying) as reported by an old HLDS version: "208.64.200.117", "208.64.200.118". The new HLDS version supposedly reports "none". 
:
;Source
:hl2master.steampowered.com:27011 (numeric IP may change)
:This domain name points to 3 A records (IPs), one of them using a different port (27015) according to the MasterServer2.vdf.
;Rag Doll Kung Fu
:See MasterServer2.vdf below.
;Red Orchestra
:Unknown - same as Source?
;SiN 1 Multiplayer
:69.28.151.162:27010 - still current?
If you can, get your application to check the file Steam\config\MasterServer2.vdf to get the latest list of master servers.
=== Reply format ===
The reply always starts with FF FF FF FF 66 0A.
The format is then a series of these server address blocks:
Type 	Data
Byte 	First octet of IP address
Byte 	Second octet of IP address
Byte 	Third octet of IP address
Byte 	Fourth octet of IP address
Unsigned Short	Port number - usually 27015 (69 87) - this is network ordered, which is unlike every other Steam protocol.
Some of the servers may be unreachable, so query each server directly to find out. Note also that this list is not exhaustive, so if you're looking for a particular type of server make sure that you specify a filter with the query, rather than filtering client side.
=== End of IP address list ===
The full requested IP list may not fit in 1 x packet. Subsequent packets must be requested by using the last received IP address and Port as the 'seed' in the next request.
The end of the IP list is indicated by a received IP address of 0.0.0.0 Port:0.
=== Implementations ===
* Asynchronous Game Query Library A Java based Asynchronous Game Query Library powered by Netty
* Steam Condenser - a multi-language library for querying the Steam Community, Source and GoldSrc game servers as well as the Steam master servers. Currently it is implemented in Java, PHP and Ruby.
* Master Server Query Protocol/Parsing packet - an example code for parsing the packet (presumably Visual Basic).
* User:Pizzahut/msqp.php - a code example for querying a Half-Life master server using the PHP language.
* QueryMaster C# library
* Steam Server Query Javascript (Node.js) module which implements the Master Server Query Protocol and Game Server Queries
* vmsq Node.js implementation for querying master servers
* msq-rs Rust library implementation for querying master servers
* @fabricio-191/valve-server-query Server, Master Server and RCON protocols implementation for Node.js
* Rust-GameDig Rust library implementation for querying master servers.
== Game server to master server ==
=== Join ===
Shortly after a game server has been initialized, it picks two master servers to "join." In order for clients to see a particular game server when they click on the "Internet" tab, the game server must be present in the Steam master servers' records.
The game server sends each master server "q" (71).
The master servers each respond by sending FF FF FF FF 73 0A followed by a (relatively) unique 4-byte "challenge" number. If you send the master servers an invalid challenge, you will get another challenge as a response.
=== Challenge response ===
After receiving the challenge packet, the game server then sends its challenge information in the following format:
====Goldsource====
 002a 30 0a 5c 70 72 6f 0.\pro
 0030 74 6f 63 6f 6c 5c 34 37 5c 63 68 61 6c 6c 65 6e tocol\47\challen
 0040 67 65 5c 31 33 33 39 38 39 35 37 30 32 5c 70 6c ge\1339895702\pl
 0050 61 79 65 72 73 5c 30 5c 6d 61 78 5c 32 5c 62 6f ayers\0\max\2\bo
 0060 74 73 5c 30 5c 67 61 6d 65 64 69 72 5c 63 73 74 ts\0\gamedir\cst
 0070 72 69 6b 65 5c 6d 61 70 5c 64 65 5f 64 75 73 74 rike\map\de_dust
 0080 5c 74 79 70 65 5c 64 5c 70 61 73 73 77 6f 72 64 \type\d\password
 0090 5c 30 5c 6f 73 5c 6c 5c 73 65 63 75 72 65 5c 30 \0\os\l\secure\0
 00a0 5c 6c 61 6e 5c 30 5c 76 65 72 73 69 6f 6e 5c 31 \lan\0\version\1
 00b0 2e 31 2e 32 2e 35 2f 53 74 64 69 6f 5c 72 65 67 .1.2.5/Stdio\reg
 00c0 69 6f 6e 5c 32 35 35 5c 70 72 6f 64 75 63 74 5c ion\255\product\
 00d0 63 73 74 72 69 6b 65 0a cstrike.
The challenge number is simply the challenge sent by the master server converted to an int.
==== Source ====
 002a 30 0a 5c 70 72 6f 0.\pro
 0030 74 6f 63 6f 6c 5c 37 5c 63 68 61 6c 6c 65 6e 67 tocol\7\challeng
 0040 65 5c 31 33 33 39 36 31 38 32 33 5c 70 6c 61 79 e\133961823\play
 0050 65 72 73 5c 30 5c 6d 61 78 5c 32 5c 62 6f 74 73 ers\0\max\2\bots
 0060 5c 30 5c 67 61 6d 65 64 69 72 5c 63 73 74 72 69 \0\gamedir\cstri
 0070 6b 65 5c 6d 61 70 5c 64 65 5f 64 75 73 74 5c 70 ke\map\de_dust\p
 0080 61 73 73 77 6f 72 64 5c 30 5c 6f 73 5c 6c 5c 6c assword\0\os\l\l
 0090 61 6e 5c 30 5c 72 65 67 69 6f 6e 5c 32 35 35 5c an\0\region\255\
 00a0 74 79 70 65 5c 64 5c 73 65 63 75 72 65 5c 30 5c type\d\secure\0\
 00b0 76 65 72 73 69 6f 6e 5c 31 2e 30 2e 30 2e 32 38 version\1.0.0.28
 00c0 5c 70 72 6f 64 75 63 74 5c 63 73 74 72 69 6b 65 \product\cstrike
 00d0 0a .
The challenge number is simply the challenge sent by the master server converted to an int.
==== Orangebox ====
0000 30 0a 5c 70 72 6f 74 6f 63 6f 6c 5c 37 5c 63 68 0.\protocol\7\ch
0010 61 6c 6c 65 6e 67 65 5c 31 39 35 39 36 38 37 33 allenge\19596873
0020 39 39 5c 70 6c 61 79 65 72 73 5c 31 5c 6d 61 78 99\players\1\max
0030 5c 34 5c 62 6f 74 73 5c 30 5c 67 61 6d 65 64 69 \4\bots\0\gamedi
0040 72 5c 74 66 5c 6d 61 70 5c 61 72 65 6e 61 5f 62 r\tf\map\arena_b
0050 61 64 6c 61 6e 64 73 5c 70 61 73 73 77 6f 72 64 adlands\password
0060 5c 30 5c 6f 73 5c 77 5c 6c 61 6e 5c 31 5c 72 65 \0\os\w\lan\1\re
0070 67 69 6f 6e 5c 2d 31 5c 67 61 6d 65 74 79 70 65 gion\-1\gametype
0080 5c 61 72 65 6e 61 5c 74 79 70 65 5c 6c 5c 73 65 \arena\type\l\se
0090 63 75 72 65 5c 30 5c 76 65 72 73 69 6f 6e 5c 31 cure\0\version\1
00a0 2e 30 2e 34 2e 33 5c 70 72 6f 64 75 63 74 5c 74 .0.4.3\product\t
00b0 66 0a f.
The challenge number is simply the challenge sent by the master server converted to an int.
==== Differences ====
The field order is a bit different with Source than with Goldsource.
Goldsource	protocol	challenge	players	max	bots	gamedir	map	type 	password	os 	secure	lan 	version	region 	product
Source 	protocol	challenge	players	max	bots	gamedir	map	password	os 	lan	region	type	secure 	version	product
=== Heartbeat ===
A "heartbeat" occurs every five minutes in order to let the master servers know that a game server is still "alive". The game server simply goes through the process of "joining" the master server list again.
=== Quit ===
;Goldsource:The game server sends the master server 62 0A to signal that the game server has shut down.
;Source:The game server sends the master server 62 0A 00 to signal that the game server has shut down.
== Steam web API as alternative to querying a master server ==
There are two "GetServerList" methods for the Steam web API. One requires a "publisher API key". The other one works with any (personal) Steam web API key, but is undocumented. 
=== Notes ===
* A Steam web API key should probably be kept private. E.g. a third-party server browser should ask the user for his or her Steam web API key, instead of using the developer's. If the API key of a developer is publicly accessible, it might be a good idea that he or she requests a new one and keeps it private.
* It may be a good idea to keep queries to the Steam web API as infrequent as possible. E.g. game server info can be updated using an A2S_INFO server query.
== See also ==
* Server Queries
* Source RCON Protocol
Category:Steam
Category:Networking