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A compiler for compiling C# to Udon assembly

UdonSharp is a compiler that compiles C# to Udon assembly. UdonSharp is not currently conformant to any version of the C# language specification, so there are many things that are not implemented or will not work.

C# features supported

  • Flow control
    • Supports: if else while for do foreach switch return break continue ternary operator (condition ? true : false) ??
  • Implicit and explicit type conversions
  • Arrays and array indexers
  • All builtin arithmetic operators
  • Conditional short circuiting (true || CheckIfTrue()) will not execute CheckIfTrue()
  • typeof()
  • Extern methods with out or ref parameters (such as many variants of Physics.Raycast())
  • User defined methods with parameters and return values, supports out/ref, extension methods, and params
  • User defined properties
  • Static user methods
  • UdonSharpBehaviour inheritence, virtual methods, etc.
  • Unity/Udon event callbacks with arguments. For instance, registering a OnPlayerJoined event with a VRCPlayerApi argument is valid.
  • String interpolation
  • Field initializers
  • Jagged arrays
  • Referencing other custom UdonSharpBehaviour classes, accessing fields, and calling methods on them
  • Recursive method calls are supported via the [RecursiveMethod] attribute

Differences from regular Unity C# to note

  • For the best experience making UdonSharp scripts, make your scripts inherit from UdonSharpBehaviour instead of MonoBehaviour
  • If you need to call GetComponent<UdonBehaviour>() you will need to use (UdonBehaviour)GetComponent(typeof(UdonBehaviour)) at the moment since the generic get component is not exposed for UdonBehaviour yet. GetComponent<T>() works for other Unity component types though.
  • Udon currently only supports array [] collections and by extension UdonSharp only supports arrays at the moment. It looks like they might support List<T> at some point, but it is not there yet.
  • Field initilizers are evaluated at compile time, if you have any init logic that depends on other objects in the scene you should use Start for this.
  • Use the UdonSynced attribute on fields that you want to sync.
  • Numeric casts are checked for overflow due to UdonVM limitations
  • The internal type of variables returned by .GetType() will not always match what you may expect since U# abstracts some types in order to make them work in Udon. For instance, any jagged array type will return a type of object[] instead of something like int[][] for a 2D int jagged array.

Udon bugs that affect U#




  1. Read the getting started with Udon doc page this has basic installation instructions for Udon.
  2. Install the latest version of the VRCSDK3 linked on the getting started.
  3. Get the latest release of UdonSharp from here and install it to your project.

Getting started

  1. Make a new object in your scene
  2. Add an Udon Behaviour component to your object
  3. Below the "New Program" button click the dropdown and select "Udon C# Program Asset"
  4. Now click the New Program button, this will create a new UdonSharp program asset for you
  5. Click the Create Script button and choose a save destination and name for the script.
  6. This will create a template script that's ready for you to start working on, open the script in your editor of choice and start programming

Asset explorer asset creation

Instead of creating assets from an UdonBehaviour you can also do the following:

  1. Right-click in your project asset explorer
  2. Navigate to Create > U# script
  3. Click U# script, this will open a create file dialog
  4. Choose a name for your script and click Save
  5. This will create a .cs script file and an UdonSharp program asset that's set up for the script in the same directory

Example scripts

The rotating cube demo

This rotates the object that it's attached to by 90 degrees every second

using UnityEngine;
using UdonSharp;

public class RotatingCubeBehaviour : UdonSharpBehaviour
private void Update()
transform.Rotate(Vector3.up, 90f * Time.deltaTime);

Other examples

For more example scripts take a look at the wiki page for examples, the Examples folder included with U#, or the community resources page on the wiki.


  • See for people who have helped provide improvments to UdonSharp
  • The open source project Harmony helps Udonsharp provide a better editor experience