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Creating a SMAPI mod

Ready to make your own mod? This page will help you create your first 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:

  1. Create an empty C# class library project.
  2. Target .NET Framework 4.5 (for Linux compatibility).
  3. Reference the Pathoschild.Stardew.ModBuildConfig NuGet package to automatically add the right references depending on the platform the mod is being compiled on.
  4. Create an entry class which subclasses StardewModdingAPI.Mod.
  5. Override the Entry method, and write your code using the SMAPI events and APIs.
  6. Create a manifest.json file which describes your mod for SMAPI.
  7. 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?
  • 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.
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. :)
What do I need?
Before you start:
  • You should read the intro to using mods to learn the basic concepts and install SMAPI.
  • You should install:
  • If you're not familiar with Visual Studio 2017 (on Windows) or MonoDevelop (on Linux/Mac), the IDE primer subguide 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

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

Configure the build

  1. 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.
  2. (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.

  1. Add a file named manifest.json to your project.
  2. 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.

  1. Add a C# class file called ModEntry.cs to your project.
  2. 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>Initialise the mod.</summary>
            /// <param name="helper">Provides methods for interacting with the mod directory, such as read/writing a config file or custom JSON files.</param>
            public override void Entry(IModHelper helper)
            {
                ControlEvents.KeyPressed += this.ReceiveKeyPress;
            }
    
    
            /*********
            ** 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 ReceiveKeyPress(object sender, EventArgsKeyPressed e)
            {
                this.Monitor.Log($"Player pressed {e.KeyPressed}.");
            }
        }
    }
    

Try your mod

  1. Build the project.
  2. Copy your mod into your game’s Mods folder (only if you didn’t do step 2 of configure the build).
    1. In the game’s Mods directory, add a folder with your mod’s name.
    2. Copy your manifest.json and compiled files (see how to find them) into the folder you created.
  3. 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:

example log output

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.ReceiveAfterLoad;

Then declare a method like this. (The EventArgs e argument will often provide more details about what happened, if there are any.)

/// <summmary>The event handler called after the player loads their save.</summary>
/// <param name="sender">The event sender.</param>
/// <param name="e">The event arguments.</param>
public void ReceiveAfterLoad(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:

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.

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

  1. 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;
       }
    }
    
  2. 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.

For more advanced config and JSON scenarios, see advanced configuration which covers…

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:

You should avoid calling 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.

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:

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:

  1. 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.)

  2. 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");
    
  3. 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.

  1. Copy your compiled mod and manifest.json into a folder matching your mod’s name.
  2. 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
    
  3. 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:

  1. Open StardewValley.exe in dotPeek.
  2. 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:

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