Your First Mod

This chapter uses the official template to write a minimal Mod that UMM can load — from scratch.

Template Structure

MyFirstMod/
├── MyFirstMod.csproj     # Project file
├── src/
│   ├── Main.cs           # Main Mod class
│   ├── Settings.cs       # Mod settings class
│   ├── Patches.cs        # Harmony patches
│   └── ResourceLoader.cs # Resource loader
├── Info.json             # UMM Mod info file
└── Properties/
    └── AssemblyInfo.cs   # Assembly info

Understanding the Entry Point: Main.cs

UMM starts your Mod through the static Load method:

using System.Reflection;
using HarmonyLib;
using UnityModManagerNet;

namespace MyFirstMod
{
    public static class Main
    {
        public static UnityModManager.ModEntry? Mod { get; private set; }
        public static Harmony? Harmony { get; private set; }
        public static Settings Settings { get; private set; } = null!;

        public static bool Load(UnityModManager.ModEntry modEntry)
        {
            Mod = modEntry;
            Settings = Settings.Load(modEntry);

            modEntry.OnToggle = OnToggle;
            modEntry.OnGUI = Settings.OnGUI;
            modEntry.OnSaveGUI = Settings.OnSaveGUI;

            Harmony = new Harmony(modEntry.Info.Id);
            modEntry.Logger.Log("Mod loaded");
            return true;
        }

        private static bool OnToggle(UnityModManager.ModEntry modEntry, bool value)
        {
            if (value)
            {
                modEntry.Logger.Log("Mod enabled");
                Harmony?.PatchAll(Assembly.GetExecutingAssembly());
            }
            else
            {
                modEntry.Logger.Log("Mod disabled");
                Harmony?.UnpatchAll(modEntry.Info.Id);
            }
            return true;
        }
    }
}

Writing Info.json

UMM reads Info.json to identify your Mod. It tells UMM: what the Mod is called, and how to load it. Without it, the Mod won't be recognized.

Create Info.json in the project root:

{
  "Id": "MyFirstMod",
  "DisplayName": "My First Mod",
  "Author": "you",
  "Version": "1.0.0",
  "ManagerVersion": "0.27.0",
  "AssemblyName": "MyFirstMod.dll",
  "EntryMethod": "MyFirstMod.Main.Load",
  "HomePage": "https://github.com/adofaiex/MyFirstMod"
}

Field	Meaning
Id	Unique Mod identifier — must not conflict with other Mods
DisplayName	Name shown in the UMM list
Author	Author name
Version	Version number — follow semantic versioning
ManagerVersion	Minimum required UMM version
AssemblyName	Filename of the compiled DLL
EntryMethod	Entry method, format Namespace.Class.Method
HomePage	Homepage / repository URL (optional)

EntryMethod must point to the static Load method of the Main class — UMM uses it to start the Mod.

Key Points

• Load — Called when UMM loads the Mod; returning true means success
• OnToggle — Called when the player enables/disables the Mod in UMM; on enable, PatchAll applies all Harmony patches
• ModEntry — The entry object carrying Mod info, logging, and callback interfaces
• Info.json — The manifest file UMM uses to identify the Mod; EntryMethod and AssemblyName must match reality

What You Learned

• The template project structure
• The meaning of each Info.json field
• The UMM Mod lifecycle: Load → OnToggle

Next Step

Learn to compile, deploy, and debug your Mod → Build, Deploy & Debug