System Messages

This page describes the system messages structure, all kind of system messages available and its purpose.

Message ID	Name
0	Unused
1	NETMSG_INFO
2	NETMSG_MAP_CHANGE
3	NETMSG_MAP_DATA
4	NETMSG_CON_READY
5	NETMSG_SNAP
6	NETMSG_SNAPEMPTY
7	NETMSG_SNAPSINGLE
8	Unused
9	NETMSG_INPUTTIMING
10	NETMSG_RCON_AUTH_ON
11	NETMSG_RCON_LINE
12	Unused
13	Unused
14	NETMSG_READY
15	NETMSG_ENTERGAME
16	NETMSG_INPUT
17	NETMSG_RCON_CMD
18	NETMSG_RCON_AUTH
19	NETMSG_REQUEST_MAP_DATA
20	Unused
21	Unused
22	NETMSG_PING
23	NETMSG_PING_REPLY
24	Unused
25	NETMSG_RCON_CMD_ADD
26	NETMSG_RCON_CMD_REM

1 - NETMSG_INFO

The first message sent by the client. It gives the server the client's version and optional password.

• Vital : ✅
• Instant Sending : ✅
• Sending Path : Client -> Server

Structure:

Field	Type	Description
Version	String	The client version string.
Password	String	The server password, if needed. May be empty.
Client Version	Integer	A numeric client version identifier.

2 - NETMSG_MAP_CHANGE

Sent by the server when the client should switch to a different map.

• Vital : ✅
• Instant Sending : ✅
• Sending Path : Server -> Client

Structure:

Field	Type	Description
Map Name	String	The name of the map.
Map CRC	Integer	The CRC checksum of the map.
Map Size	Integer	Total map size in bytes.
Chunks Per Request	Integer	Number of map chunks the server sends per NETMSG_REQUEST_MAP_DATA request.
Chunk Size	Integer	Size of each map chunk in bytes.
Map SHA256	Binary (32 bytes)	SHA256 digest of the map.

3 - NETMSG_MAP_DATA

Sent by the server to transfer a raw chunk of the map file.

• Vital : ✅
• Instant Sending : ✅
• Sending Path : Server -> Client

Structure:

Field	Type	Description
Data	Binary	Raw map chunk data.

4 - NETMSG_CON_READY

Sent by the server when the connection is ready and the client should send its start info.

• Vital : ✅
• Instant Sending : ✅
• Sending Path : Server -> Client

Structure:

Empty payload

5 - NETMSG_SNAP

This message sends a slice of a snap with part of the items.

• Vital : ❌
• Instant Sending : ✅
• Sending Path : Server -> Client

INFO

Snap is a complex type of chunk. You can find more information about it on Snap Structure page.

6 - NETMSG_SNAPEMPTY

This message sends an empty snap with no items.

• Vital : ❌
• Instant Sending : ✅
• Sending Path : Server -> Client

INFO

Snap is a complex type of chunk. You can find more information about it on Snap Structure page.

7 - NETMSG_SNAPSINGLE

This message sends a full snap with all items in a single packet.

• Vital : ❌
• Instant Sending : ✅
• Sending Path : Server -> Client

INFO

Snap is a complex type of chunk. You can find more information about it on Snap Structure page.

9 - NETMSG_INPUTTIMING

This message is a response from the server to the client "INPUT" chunk, reporting how early or late the input was handled.

• Vital : ❌
• Instant Sending : ❌
• Sending Path : Server -> Client

Structure:

Field	Type	Description
Intended Tick	Integer	The game tick the client intended its input for.
Time Left	Integer	Time left before the intended tick, in milliseconds. Negative values mean the input was late.

INFO

Check the Input & Input Timing Chunks section for more information about this chunk.

10 - NETMSG_RCON_AUTH_ON

Sent by the server to indicate that the client has been authenticated for rcon.

• Vital : ✅
• Instant Sending : ❌
• Sending Path : Server -> Client

Structure:

Empty payload

11 - NETMSG_RCON_LINE

Sent by the server to print a line to the remote console on the client.

• Vital : ✅
• Instant Sending : ❌
• Sending Path : Server -> Client

Structure:

Field	Type	Description
Line	String	The text line to print in the client's remote console.

14 - NETMSG_READY

Sent by the client after it has loaded the map and is ready.

• Vital : ✅
• Instant Sending : ✅
• Sending Path : Client -> Server

Structure:

Empty payload

15 - NETMSG_ENTERGAME

Sent by the client to tell the server to start sending snapshots.

• Vital : ❌
• Instant Sending : ✅
• Sending Path : Client -> Server

Structure:

Empty payload

16 - NETMSG_INPUT

This message is sent by the client to the server with the player's input.

• Vital : ❌
• Instant Sending : ✅
• Sending Path : Client -> Server

Structure:

Field	Type	Description
Ack Game Tick	Integer	The last acknowledged server game tick.
Prediction Tick	Integer	The game tick the client is predicting with this input.
Input Size	Integer	Total size of the raw input data in bytes.
Input -> Direction	Integer	Direction the player is moving: -1 = left, 0 = neutral, 1 = right.
Input -> Target X	Integer	X coordinate of the crosshair / target position.
Input -> Target Y	Integer	Y coordinate of the crosshair / target position.
Input -> Jump	Integer	Jump input state.
Input -> Fire	Integer	Fire input state.
Input -> Hook	Integer	Hook input state.
Input -> PlayerFlags	Integer	Player flags for this input (e.g. chatting, scoreboard).
Input -> WantedWeapon	Integer	Direct weapon slot selection. 0 = no desired weapon, 1+weapon = desired weapon.
Input -> NextWeapon	Integer	Next weapon cycle input.
Input -> PrevWeapon	Integer	Previous weapon cycle input.
Ping Correction	Integer	Client-reported ping correction for latency calculation.

INFO

Check the Input & Input Timing Chunks section for more information about this chunk.

17 - NETMSG_RCON_CMD

Sent by the client to execute a command on the server through the remote console.

• Vital : ✅
• Instant Sending : ❌
• Sending Path : Client -> Server

Structure:

Field	Type	Description
Command	String	The command to be executed.

18 - NETMSG_RCON_AUTH

Sent by the client to authenticate for rcon access, containing the password.

• Vital : ✅
• Instant Sending : ❌
• Sending Path : Client -> Server

Structure:

Field	Type	Description
Password	String	The rcon password used to authenticate.

19 - NETMSG_REQUEST_MAP_DATA

Sent by the client to request the next chunk of map data.

• Vital : ✅
• Instant Sending : ✅
• Sending Path : Client -> Server

Structure:

Field	Type	Description
Chunk	Integer	The map chunk index being requested.

22 - NETMSG_PING

Sent by either side to request a pong response.

• Vital : ❌
• Instant Sending : ❌
• Sending Path : Both ways

Structure:

Empty payload

23 - NETMSG_PING_REPLY

Sent by either side as a reply to a NETMSG_PING.

• Vital : ❌
• Instant Sending : ❌
• Sending Path : Both ways

Structure:

Empty payload

25 - NETMSG_RCON_CMD_ADD

Sent by the server to inform an authenticated client about a newly available rcon command.

• Vital : ✅
• Instant Sending : ❌
• Sending Path : Server -> Client

Structure:

Field	Type	Description
Name	String	Command name.
Help	String	Help text describing the command.
Params	String	Parameter format string for the command.

26 - NETMSG_RCON_CMD_REM

Sent by the server to inform an authenticated client that a rcon command is no longer available.

• Vital : ✅
• Instant Sending : ❌
• Sending Path : Server -> Client

Structure:

Field	Type	Description
Name	String	Name of the command to remove.

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