bool IsClient()

Returns true if the script is running on a client.

Any running instance of ZDoom that has display and input capabilities is considered as a client.

If the instance is a client, graphics effects (clientside actors and hud) should be enabled for it.

The following are clients:

• A singleplayer game.
• A client in client-server Zandronum multiplayer (but not the server).
• A client that is also acting as a server for other clients (this mode is not supported in Zandronum yet but other game engines have it).

Using IsClient and IsServer ensures that your mod runs correctly in both singleplayer and multiplayer:

if (IsServer())
{
    // Run serverside code.
}
if (IsClient())
{
    // Run clientside code.
}