// Required for uMod (Oxide) API
using Oxide.Core;

// Namespace for the plugin
namespace Oxide.Plugins
{
    // Plugin basic information
    [Info("Hello World", "YourName", "1.0.0")]
    [Description("Displays a welcome message when a player logs in.")]

    // Main class that inherits from RustPlugin
    class HelloWorld : RustPlugin
    {
        // Hook called when a player has finished initializing
        void OnPlayerInit(BasePlayer player)
        {
            // Check if the player object is not null and is connected
            if (player != null && player.IsConnected)
            {
                // Send a message to the target player's chat
                player.ChatMessage("hello world");
            }
        }
    }
}

Already use WelcomeMessages plugin since 2016

pookins

Already use WelcomeMessages plugin since 2016

This was all written by generative AI.
Can I use plugins that are not approved by umod on my server?

That hook doesn't exist, it hasn't for years I believe.

Yes you can use any plugins just put them in oxide/plugins folder

OnPlayerInit

That hook was changed years ago.. AI is Old Code and should be only used as a helper not to code hole plugins.

it now

void OnPlayerConnected(BasePlayer player)

I created a plugin that executes certain commands when the player performs certain actions, and it's working well.