Modding:Modder Guide/Tutorial Mod

Ready to make your own mod? This page will help you create your first SMAPI mod and use the available APIs and events.

Quick start

The rest of this page will help you create a mod. If you're experienced enough to skip the tutorial, here's a quick summary of what this page will walk you through:

Create an empty C# class library project.
Target .NET Framework 4.5 (for Linux compatibility).
Reference the Pathoschild.Stardew.ModBuildConfig NuGet package to automatically add the right references depending on the platform the mod is being compiled on.
Create an entry class which subclasses StardewModdingAPI.Mod.
Override the Entry method, and write your code using the SMAPI events and APIs.
Create a manifest.json file which describes your mod for SMAPI.
Create a zip file containing the mod files for release.

Intro

What is SMAPI?
A SMAPI mod uses the SMAPI modding API to extend the game logic. You can run code when something happens (e.g. mouse clicked or menu opened), or periodically (e.g. once per game tick). SMAPI mods are written in C# using the .NET Framework. Stardew Valley also uses XNA (on Windows) or MonoGame (on Linux and Mac) for the fundamental game logic (drawing to the screen, user input, etc).

Can I make a mod?
The next few sections will walk you through creating a very simple mod. If you follow along, you'll have created a mod! All that will be left is making it do what you want.
- Scenario A: you're new to programming.
  Many mod developers start with little or no programming experience. You can certainly learn along the way if you're determined, but you should be prepared for a steep learning curve. Don't be too ambitious at first; it's better to start with a small mod when you're figuring it out. It's easy to become overwhelmed at first and give up. The modding community is very welcoming, so don't be afraid to ask questions!
  Since mods are written in C#, it's a good idea to get acquainted with it first. C# Fundamentals for Absolute Beginners will walk you through the basics of C# needed to write SMAPI mods, from the basic concepts to event-driven programming (which is what SMAPI mods use).
- Scenario B: you already have programming experience.
  You should be fine. Programming experience in C# or Java will make things easier, but it isn't critical. If you're unfamiliar with C#, you can skim through C# Fundamentals for Absolute Beginners to fill in any gaps.

What do I need?
Before you start:
1. You should read the intro for players to learn the basic concepts and install SMAPI.
2. You should install:
  1. Stardew Valley;
  2. SMAPI;
  3. and Visual Studio 2017 Community (on Windows) or MonoDevelop (on Linux/Mac).
3. If you're not familiar with Visual Studio 2017 (on Windows) or MonoDevelop (on Linux/Mac), Modding:IDE reference explains how to do the important stuff you need for this guide.

Where can I get help?
The Stardew Valley modding community is very welcoming. Feel free to come chat on Discord or post in the forums.

Create a mod

A SMAPI mod is a compiled library (DLL) with an entry method that gets called by SMAPI, so let's set that up.

Create the project

Open Visual Studio 2017 or MonoDevelop.
Create a solution with a C# class library project (see how to).
Change the target framework to .NET Framework 4.5 for compatibility with Linux (see how to).
Delete the Class1.cs or MyClass.cs file (see how to).

Configure the build

Reference the Pathoschild.Stardew.ModBuildConfig NuGet package (see how to). This will automatically configure your project to load the right modding dependencies for the current platform, so your mod can be built on Linux, Mac, or Windows. It also adds support for debugging the mod in-game.
(optional) See simplify mod development to automatically package your mod into your mod folder and enable debugging while the game is running.

That's it! Try building the project and make sure you don't get any errors. If you get an error like "failed to find the game install path", see the package's Troubleshooting section.

Add your manifest

The mod manifest tells SMAPI about your mod.

Add a file named manifest.json to your project.

Paste this code into the file (replacing the <...> placeholders):

{
   "Name": "<your project name>",
   "Author": "<your name>",
   "Version": {
      "MajorVersion": 1,
      "MinorVersion": 0,
      "PatchVersion": 0,
      "Build": null
   },
   "Description": "<One or two sentences about the mod>",
   "UniqueID": "<your name>.<your project name>",
   "EntryDll": "<your project name>.dll"
}

This will be listed in the console output when the game is launching. (For more info about the version number, see semantic versioning.)

Write the code

Almost done! Now for the code SMAPI will run.

Add a C# class file called ModEntry.cs to your project.

Put this code in the file (replace <your project name> with the name of your project):

using System;
using Microsoft.Xna.Framework;
using StardewModdingAPI;
using StardewModdingAPI.Events;
using StardewValley;
namespace <your project name>
{
    /// <summary>The mod entry point.</summary>
    public class ModEntry : Mod
    {
        /*********
        ** Public methods
        *********/
        /// <summary>The mod entry point, called after the mod is first loaded.</summary>
        /// <param name="helper">Provides simplified APIs for writing mods.</param>
        public override void Entry(IModHelper helper)
        {
            ControlEvents.KeyPressed += this.ControlEvents_KeyPress;
        }

        /*********
        ** Private methods
        *********/
        /// <summary>The method invoked when the player presses a keyboard button.</summary>
        /// <param name="sender">The event sender.</param>
        /// <param name="e">The event data.</param>
        private void ControlEvents_KeyPress(object sender, EventArgsKeyPressed e)
        {
            this.Monitor.Log($"Player pressed {e.KeyPressed}.");
        }
    }
}

Try your mod

Build the project.
Copy your mod into your game's Mods folder (only if you didn't do step 2 of configure the build).
In the game's Mods directory, add a folder with your mod's name.
Copy your manifest.json and compiled files (see how to find them) into the folder you created.
Run the game through SMAPI.

The mod so far will just send a message to the console window whenever you press a key in the game. If that didn't work, something went wrong. Try reviewing the above instructions, or ask for help. :)

Mod APIs

Now that you have a basic mod, here are the SMAPI features you can use to do more.

Events

SMAPI publishes several C# events that tell you when something happens. For example, if you want to do something after the player loads their save, you can add this to your Entry method:

SaveEvents.AfterLoad += this.SaveEvents_AfterLoad;

Then declare a method like this. (The EventArgs e argument contains any extra data about the event.)

/// <summary>The method called after the player loads their save.</summary>
/// <param name="sender">The event sender.</param>
/// <param name="e">The event arguments.</param>
public void SaveEvents_AfterLoad(object sender, EventArgs e)
{
   this.Monitor.Log("The player loaded their game! This is a good time to do things.");
   this.Monitor.Log("Everything in the world is ready to interact with at this point.");
}

Here are the available events:

ContentEvents are raised when the game loads content from its XNB files or changes locale.

event summary

AfterLocaleChanged Raised after the content language changes.

ControlEvents are raised when the player uses a controller, keyboard, or mouse. They're raised before the game handles the input, so it's possible to selectively prevent the game from responding to it. (That's beyond the scope of this guide, but it involves overwriting Game1.oldKBState, Game1.oldMouseState, and Game1.oldPadState.) Most of these events are split into two variants, XPressed and XReleased. The Pressed variant is raised when the player presses the button (holding the button down only triggers the event once), and the Released variant is raised when they release it.

event	summary
ControllerButtonPressed ControllerButtonReleased	Raised after the player pressed/released a button on a gamepad or controller. These events aren't raised for trigger buttons.
ControllerTriggerPressed ControllerTriggerReleased	Raised after the player pressed/released a trigger button on a gamepad or controller.
KeyPressed KeyReleased	Raised after the player pressed/released a keyboard key.
KeyboardChanged	Raised after the game's `KeyboardState` changed. That happens when the player presses or releases a key.
MouseChanged	Raised after the game's `MouseState` changed. That happens when the player moves the mouse, scrolls the mouse wheel, or presses/releases a button.

GameEvents are raised when the game changes state.

event	summary
GameLoaded	Raised when the game is ready and initialised. At this point the game data (like `Game1.objectInformation`) is in memory and ready for use.
UpdateTick	Raised when the game updates its state (≈60 times per second).
SecondUpdateTick	Raised every other tick (≈30 times per second).
FourthUpdateTick	Raised every fourth tick (≈15 times per second).
EighthUpdateTick	Raised every eighth tick (≈8 times per second).
QuarterSecondTick	Raised every 15th tick (≈4 times per second).
HalfSecondTick	Raised every 30th tick (≈twice per second).
OneSecondTick	Raised every 60th tick (≈once per second).

GraphicsEvents are raised during the game's draw loop, when the game is rendering content to the window.

event	summary
OnPreRenderEvent OnPostRenderEvent	Raised before and after drawing the world to the screen.
OnPreRenderGuiEvent OnPostRenderGuiEvent	When a menu is open (`Game1.activeClickableMenu != null`), raised before and after drawing that menu to the screen. This includes the game's internal menus like the title screen.
OnPreRenderHudEvent OnPostRenderHudEvent	Raised before and after drawing the HUD (item toolbar, clock, etc) to the screen. The HUD is available at this point, but not necessarily visible. (For example, the event is called even if a menu is open.)
Resize	Raised after the game window is resized.

LocationEvents are raised when the player transitions between game locations, a location is added or removed, or the objects in the current location change.

event	summary
CurrentLocationChanged	Raised after the player warps to a new location. Handlers are given the previous and new locations as arguments.
LocationObjectsChanged	Raised after the list of objects in the current location changes (e.g. an object is added or removed). Handlers are given the new list of objects as an argument.
LocationsChanged	Raised after a game location is added or removed. Handlers are passed the new list of locations as an argument.

MenuEvents are raised when a game menu is opened or closed (including internal menus like the title screen).

event	summary
MenuChanged	Raised after a game menu is opened or replaced with another menu. This event is not invoked when a menu is closed. Handlers are given the previous menu (if any) and new menu (if any).
MenuClosed	Raised after a game menu is closed. Handlers are given the previous menu.

MineEvents are raised when something happens in The Mines.

event summary

MineLevelChanged Raised after the player warps to a new level of the mine. Handlers are passed the previous and new mine level as arguments.

PlayerEvents are raised when the player data changes.

event	summary
InventoryChanged	Raised after the player's inventory changes in any way (added or removed item, sorted, etc).
LeveledUp	Raised after the player levels up a skill. This happens as soon as they level up, not when the game notifies the player after their character goes to bed.

SaveEvents are raised when the player saves or loads the game.

event	summary
AfterLoad	Raised after the player loads a saved game. The world is ready for mods to modify at this point.
BeforeSave	Raised before the game updates the save file. (The save won't be written until all mods have finished handling this event.)
AfterSave	Raised after the game finishes updating the save file.
AfterReturnToTitle	Raised after the player exits to the title screen.

TimeEvents are raised when the in-game date or time changes.

event	summary
AfterDayStarted	Raised after the game begins a new day, including when loading a save.
TimeOfDayChanged	Raised after the in-game clock changes.
DayOfMonthChanged	Not recommended; most mods should use `AfterDayStarted` instead. Raised when `Game1::dayOfMonth` changes value. This happens before the new day starts. If you exit to title and then reload the same save, it will not trigger since the value hasn't changed.
SeasonOfYearChanged	Raised after the season changes.
YearOfGameChanged	Raised after the year changes.

Configuration

You can let users configure your mod through a config.json file. SMAPI will automatically create the file and take care of reading, normalising, and updating it.

Basic configuration

Here's the simplest way to use config.json:

Create your model. This is just a class with properties for the config options you want, and it can contain almost anything from a few boolean fields to a complex object graph. (You should try to keep it simple for your users, though.) You can set defaults directly:

class ModConfig
{
   public bool ExampleBoolean { get; set; } = true;
   public float ExampleFloat { get; set; } = 0.5;
}

...or with a constructor:

class ModConfig
{
   public bool ExampleBoolean { get; set; }
   public float ExampleFloat { get; set; }

   public ModConfig()
   {
      this.ExampleBoolean = true;
      this.ExampleFloat = 0.5;
   }
}

In your ModEntry::Entry method, add this line to read the config options:
```
ModConfig config = helper.ReadConfig<ModConfig>();
```

That's it! When the player launches the game, SMAPI will create the config.json file automatically if it doesn't exist yet, using the default config options you provided in your model. If you need to edit and save the config, you can use helper.SaveConfig(config). You can access the helper in other methods using this.Helper.

Custom JSON files

Sometimes one config.json isn't enough, or you need to store data that's not meant to be edited by the user. This is pretty easy using the ModHelper:

Create your model (just like the previous section).
In your mod code, use this.Helper to read and write to a named file:
```
// read file
var model = this.Helper.ReadJsonFile<ModData>("data.json") ?? new ModData();

// save file (if needed)
this.Helper.WriteJsonFile("data.json", model);
```
Note that ReadJsonFile will return null if the file doesn't exist. The above example will create a default instance if that happens; if you don't want to do that, just remove the ?? new ModData() part.

Per-save JSON files

You can also specify a directory path (relative to your mod directory) instead of just the file name. The directories will be created automatically if needed. For example, here's how you'd use per-save config files:

// read file
var model = this.Helper.ReadJsonFile<ModData>($"{Constants.SaveFolderName}/config.json") ?? new ModData();

// write file (if needed)
this.Helper.WriteJsonFile($"{Constants.SaveFolderName}/config.json", model);

Content

If your mod needs custom textures or maps, you can load them with SMAPI's content API. You can load any .xnb file the game supports, or load a .png file into a texture.

Example usage:

Load an image from your mod folder (from an assets subfolder in this example):

// load an XNB file
var texture = helper.Content.Load<Texture2D>(@"assets\texture.xnb", ContentSource.ModFolder);

// load a PNG file
var texture = helper.Content.Load<Texture2D>(@"assets\texture.png", ContentSource.ModFolder);

Load an asset from game's content folder:

var data = helper.Content.Load<Dictionary<int, string>>(@"Data\ObjectInformation.xnb", ContentSource.GameContent);

Load a custom tilesheet for a map:

tilesheet.ImageSource = helper.Content.GetActualAssetKey(@"assets\tilesheet.png");

Notes:

Don't call content.Load<T> in draw code for performance reasons, since drawing happens ≈60 times per second. Instead, load your content ahead of time and reuse it.
Don't worry about which path separators you use; SMAPI will normalise them automatically.

Logging

Your mod can write messages to the console window and log file using the monitor. For example, this code:

this.Monitor.Log("a trace message", LogLevel.Trace);
this.Monitor.Log("a debug message", LogLevel.Debug);
this.Monitor.Log("an info message", LogLevel.Info);
this.Monitor.Log("a warning message", LogLevel.Warn);
this.Monitor.Log("an error message", LogLevel.Error);

will log something like this:

[18:00:00 TRACE Mod Name] a trace message

[18:00:00 DEBUG Mod Name] a debug message

[18:00:00 INFO  Mod Name] an info message

[18:00:00 WARN  Mod Name] a warning message

[18:00:00 ERROR Mod Name] an error message

Note that LogLevel.Trace messages won't appear in the console window by default, they'll only be written to the log file. Trace messages are for troubleshooting details that are useful when someone sends you their error log, but which the player normally doesn't need to see. (You can see trace messages in the console if you install the "SMAPI for developers" version.)

Reflection

SMAPI provides an API for robustly accessing the game's private fields or methods. You can use it from helper.Reflection in your entry method, or this.Helper.Reflection elsewhere in your entry class. It consists of three methods:

GetPrivateValue<TValue>(...) returns the value of a private field.
GetPrivateField<TValue>(...) returns an object you can use to get or set a field's value.
GetPrivateMethod(...) returns an object you can use to invoke a method.

Here are a few examples of what this lets you do:

// did you pet your pet today?
bool wasPet = this.Helper.Reflection.GetPrivateValue<bool>(pet, "wasPetToday");

// what is the spirit forecast today?
string forecast = this.Helper.Reflection
   .GetPrivateMethod(new TV(), "getFortuneForecast")
   .Invoke<string>();

// randomise the mines
if(Game1.currentLocation is MineShaft)
   this.Helper.Reflection.GetPrivateField<Random>(Game1.currentLocation, "mineRandom").SetValue(new Random());

This works with static or instance fields/methods, caches the reflection to improve performance, and will throw useful errors automatically when reflection fails.

If you need to do more, you can also switch to C#'s underlying reflection API:

FieldInfo field = this.Helper.Reflection.GetPrivateField<string>(…).FieldInfo;
MethodInfo method = this.Helper.Reflection.GetPrivateMethod(…).MethodInfo;

Mod registry

Your mod can get information about loaded mods, or check if a particular mod is loaded. (All mods are loaded by the time your mod's Entry(…) method is called.)

// check if a mod is loaded
bool isLoaded = this.Helper.ModRegistry.IsLoaded("UniqueModID");

// get manifest info for a mod (name, description, version, etc.)
IManifest manifest = this.Helper.ModRegistry.Get("UniqueModID");

// get manifest info for all loaded mods
foreach(IManifest manifest in this.Helper.ModRegistry.GetAll()) { … }

Final considerations

Crossplatform support

SMAPI will automatically adjust your mod so it works on Linux, Mac, and Windows. However, there are a few things you should do to avoid problems:

Use the crossplatform build config package to automatically set up your project references. This makes crossplatform compatibility easier and lets your code compile on any platform. (If you followed the above guide, you already have this.)

Use Path.Combine to build file paths, don't hardcode path separators since they won't work on all platforms.

// ✘ Don't do this! It will crash on Linux/Mac.
string path = helper.DirectoryPath + "\assets\asset.xnb";

// ✓ This is OK
string path = Path.Combine(helper.DirectoryPath, "assets", "asset.xnb");

Use helper.DirectoryPath, don't try to determine the mod path yourself.

// ✘ Don't do this! It will crash if SMAPI rewrites the assembly (e.g. to update or crossplatform it).
string modFolder = Assembly.GetCallingAssembly().Location;

// ✓ This is OK
string modFolder = helper.DirectoryPath;

Test on all platforms

If you want to test your mod on all platforms, there's some first-time setup you need to get out of the way. Essentially you need to test your mod twice: once on Windows, and again on Linux or Mac. You can do that by testing one version on your computer, and the other in a virtual machine.

If your main computer is Windows:
1. Install VirtualBox.
2. Add this premade Linux virtual machine (requires a 64-bit computer).
  In VirtualBox, click Machine » Add and choose the downloaded .vbox file. This is a Manjaro virtual machine with Chromium (web browser), Steam, and MonoDevelop preinstalled.
3. Launch the virtual machine, and install Stardew Valley from the Steam client (preinstalled) or GOG website.
  Tip: don't change the default install path, or you'll need to customise the mod's build configuration.

If your main computer is Linux or Mac:
1. Install VirtualBox.
2. Create a VM with Windows.
3. Install Visual Studio Community in your VM.
4. Install Stardew Valley in your VM.

Release your mod

Ready to share your mod with the world? Let's say you created a mod named Pineapples Everywhere which turns all NPCs into pineapples; here's how you would release it for others to use.

Copy your compiled mod and manifest.json into a folder matching your mod's name.

Create a zip archive with your mod's name and version. Your mod structure should look something like this:

PineapplesEverywhere-1.0.zip
   PineapplesEverywhere/
      PineapplesEverywhere.dll
      PineapplesEverywhere.pdb
      config.json
      manifest.json

Upload your mod to Nexus Mods, the official modding forums, or both.

Decompile the game code

When you start working on more complex mods, you may need to look at how the game code works.

Here's how to decompile the game code so you can look at it:

Open StardewValley.exe in dotPeek.
Right-click on Stardew Valley and choose Export to Project. Accept the default options to create a decompiled project you can open in Visual Studio. (Note that the decompiled code will not be functional due to limitations of the decompiler, but you'll be able to read the game code.)

Here's how to unpack the XNB data files:

Download the Easy XNB Pack/UnPack Toolkit.
Copy the entire Stardew Valley\Content game folder into XNB-Mod-Toolkit\Packed.
Run XNB-Mod-Toolkit\UNPACK FILES.bat to unpack the files into XNB-Mod-Toolkit\Unpacked.