---

name: udonsharp-coding description: A guide for coding with UdonSharp. Use this when you are asked to create or edit UdonSharp programs. Code that inherits from UdonSharpBehavior falls under UdonSharp code.

UdonSharp generally follows C# syntax, but its features are limited.

Supported C# Features

• Flow control: 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 built-in 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 an 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 Unity C#

• Udon currently only supports array [] collections and by extension UdonSharp only supports arrays at the moment.
• 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.

Instantiate

You cannot create a new GameObject using new GameObject() and similar APIs. In UdonSharp, you create new objects by cloning an existing GameObject in the scene using Instantiate(). Additionally, only GameObject can be instantiated via Instantiate().

Best Practices

Use Utilities.IsValid for null checks

bool IsValid(object obj) returns true when obj is not null (or is otherwise valid). In UdonSharp, this is faster than doing null checks with ==.

Basic Template

Copyusing UdonSharp;
using UnityEngine;
using VRC.SDKBase;
using VRC.Udon;

public class UdonSharpScript : UdonSharpBehaviour
{

}

Networking

If the problem you are addressing involves network synchronization, read the document references/en/udon_network/README.md. These documents describe the concepts and methods required to implement network logic in Udon.

Class Design

If you need shared logic, encapsulation, or inheritance, be aware that UdonSharp has important limitations. See references/en/udon_class.md.

Player Tracking

If you are implementing things like gaze-following objects or objects that follow avatar bones, see references/en/udon_playerTracking.md. It includes important notes and pitfalls for implementation.

Persistence

If you need to save player-specific data (like high scores, inventory, or settings) across sessions or instances, refer to references/en/udon_persistence.md. This document explains how to use PlayerData and PlayerObjects for persistent storage.