VRChat world development with UdonSharp (C# → Udon Assembly) has strict compile constraints that differ significantly from standard C#. Features like List<T>, async/await, try/catch, LINQ, and lambdas cause compile errors.

This repository provides AI coding agents with the knowledge to generate correct UdonSharp code from the start.

| Problem | Solution | |---------|----------| | AI generates List<T>, async/await, etc. | Rules + hooks auto-detect and warn | | Sync variable bloat | Decision tree + data budget | | Incorrect networking patterns | Pattern library + anti-patterns | | SDK version feature differences | Version table with feature mapping | | Late Joiner state inconsistency | Sync pattern selection framework |

This is NOT:

A VRChat SDK or UdonSharp distribution
A Unity project (no executable code)
A replacement for official VRChat documentation
A guarantee of all AI behaviors

Issues: Bug reports and knowledge requests are welcome via GitHub Issues. PRs: Pull Requests are not accepted. See CONTRIBUTING.md for details.

Migrating from fork/clone? — Since v1.0.0, this project is distributed as an npm package. You no longer need to fork or clone the repository. Simply run one of the install commands below inside your VRChat Unity project. If you previously cloned this repo, you can safely delete the cloned directory and switch to the npm-based install.

Method 1: skills CLI (recommended)

npx skills add niaka3dayo/agent-skills-vrc-udon

This uses the skills.sh ecosystem to install skills into your project.

Method 2: Claude Code plugin

claude plugin add niaka3dayo/agent-skills-vrc-udon

Method 3: npx direct install

npx agent-skills-vrc-udon

Options:

npx agent-skills-vrc-udon --force    # Overwrite existing files
npx agent-skills-vrc-udon --list     # Preview files to install (dry run)

Method 4: git clone

git clone https://github.com/niaka3dayo/agent-skills-vrc-udon.git

skills/                                  # All skills
  unity-vrc-udon-sharp/                 # UdonSharp core skill
    SKILL.md                              # Skill definition + frontmatter
    LICENSE.txt                           # MIT License
    CHEATSHEET.md                         # Quick reference (1 page)
    rules/                               # Constraint rules
      udonsharp-constraints.md
      udonsharp-networking.md
      udonsharp-sync-selection.md
    hooks/                               # PostToolUse validation
      validate-udonsharp.sh
      validate-udonsharp.ps1
    assets/templates/                    # Code templates (17 files)
    references/                          # Detailed documentation (22 files)
  unity-vrc-world-sdk-3/                # VRC World SDK skill
    SKILL.md, LICENSE.txt, CHEATSHEET.md, references/ (7 files)
templates/                               # AI tool config templates
  CLAUDE.md  AGENTS.md  GEMINI.md        # Distributed to users via installer
.claude-plugin/marketplace.json         # Claude Code plugin registration
CLAUDE.md                               # Development guide (this repo only)

unity-vrc-udon-sharp

UdonSharp scripting core skill. Covers compile constraints, networking, events, and templates.

| Area | Content | |------|---------| | Constraints | Blocked C# features and alternatives (List<T> → DataList, async → SendCustomEventDelayedSeconds) | | Networking | Ownership model, Manual/Continuous sync, FieldChangeCallback, anti-patterns | | NetworkCallable | SDK 3.8.1+ parameterized network events (up to 8 args) | | Persistence | SDK 3.7.4+ PlayerData/PlayerObject API | | Dynamics | SDK 3.10.0+ PhysBones, Contacts, VRC Constraints for Worlds | | Web Loading | String/Image download, VRCJson, VRCUrl constraints | | Templates | 17 templates (interactions, sync patterns, persistence, editor utilities, and more) |

unity-vrc-world-sdk-3

World-level scene setup, component placement, and optimization.

| Area | Content | |------|---------| | Scene Setup | VRC_SceneDescriptor, spawn points, Reference Camera | | Components | VRC_Pickup, Station, ObjectSync, Mirror, Portal, CameraDolly | | Layers | VRChat reserved layers and collision matrix | | Performance | FPS targets, Quest/Android limits, optimization checklist | | Lighting | Baked lighting best practices | | Audio/Video | Spatial audio, video player selection (AVPro vs Unity) | | Upload | Build and upload workflow, pre-upload checklist |

Rules are constraint files that guide AI agents before code generation.

| Rule File | Content | |-----------|---------| | udonsharp-constraints | Blocked C# features, code generation rules, attributes, syncable types | | udonsharp-networking | Ownership model, sync modes, anti-patterns, NetworkCallable constraints | | udonsharp-sync-selection | Sync decision tree, data budget targets, 6 minimization principles |

Sync Decision Tree

Q1: Visible to other players?
    No  --> No sync (0 bytes)
    Yes --> Q2

Q2: Late Joiner needs current state?
    No  --> Events only (0 bytes)
    Yes --> Q3

Q3: Continuous change? (position/rotation)
    Yes --> Continuous sync
    No  --> Manual sync (minimal [UdonSynced])

Target: < 50 bytes per behaviour. Small-medium worlds: < 100 bytes total.

PostToolUse hooks that auto-run when .cs files are edited.

| Category | Check | Severity | |----------|-------|----------| | Blocked Features | List<T>, async/await, try/catch, LINQ, coroutines, lambdas | ERROR | | Blocked Patterns | AddListener(), StartCoroutine() | ERROR | | Networking | [UdonSynced] without RequestSerialization() | WARNING | | Networking | [UdonSynced] without Networking.SetOwner() | WARNING | | Sync Bloat | 6+ synced variables per behaviour | WARNING | | Sync Bloat | int[]/float[] sync (recommend smaller types) | WARNING | | Config Mismatch | NoVariableSync mode with [UdonSynced] fields | ERROR |

Supports both Bash (validate-udonsharp.sh) and PowerShell (validate-udonsharp.ps1).

SDK Versions

| SDK Version | Key Features | Status | |:-----------:|:-------------|:------:| | 3.7.1 | StringBuilder, Regex, System.Random | Supported | | 3.7.4 | Persistence API (PlayerData / PlayerObject) | Supported | | 3.7.6 | Multi-platform Build & Publish (PC + Android) | Supported | | 3.8.0 | PhysBone dependency sorting, Force Kinematic On Remote | Supported | | 3.8.1 | [NetworkCallable] parameterized events, Others/Self targets | Supported | | 3.9.0 | Camera Dolly API, Auto Hold pickup | Supported | | 3.10.0 | VRChat Dynamics for Worlds (PhysBones, Contacts, VRC Constraints) | Supported | | 3.10.1 | Bug fixes, stability improvements | Supported | | 3.10.2 | EventTiming.PostLateUpdate/FixedUpdate, PhysBones fixes, shader time globals | Supported | | 3.10.3 | VRCPlayerApi.isVRCPlus, VRCRaycast (avatar), Mirror render-order fix | Latest Stable |

Note: SDK < 3.9.0 was deprecated on December 2, 2025. New world uploads require 3.9.0+.

Official Resources

| Resource | URL | |----------|-----| | VRChat Creators Docs | https://creators.vrchat.com/ | | UdonSharp API Reference | https://udonsharp.docs.vrchat.com/ | | VRChat Forums (Q&A) | https://ask.vrchat.com/ | | VRChat Canny (Bugs/Features) | https://feedback.vrchat.com/ | | VRChat Community GitHub | https://github.com/vrchat-community |

Issues are welcome -- bug reports and knowledge requests help improve this project.

Pull Requests are not accepted -- all fixes and updates are made by the maintainer.

See CONTRIBUTING.md for details.

This project is not affiliated with VRChat Inc. No official endorsement, partnership, or association is implied.

"VRChat", "UdonSharp",

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skills/ # All skills unity-vrc-udon-sharp/ # UdonSharp core skill SKILL.md # Skill definition + frontmatter LICENSE.txt # MIT License CHEATSHEET.md # Quick reference (1 page) rules/ # Constraint rules udonsharp-constraints.md udonsharp-networking.md udonsharp-sync-selection.md hooks/ # PostToolUse validation validate-udonsharp.sh validate-udonsharp.ps1 assets/templates/ # Code templates (17 files) references/ # Detailed documentation (22 files) unity-vrc-world-sdk-3/ # VRC World SDK skill SKILL.md, LICENSE.txt, CHEATSHEET.md, references/ (7 files) templates/ # AI tool config templates CLAUDE.md AGENTS.md GEMINI.md # Distributed to users via installer .claude-plugin/marketplace.json # Claude Code plugin registration CLAUDE.md # Development guide (this repo only)

Q1: Visible to other players? No --> No sync (0 bytes) Yes --> Q2 Q2: Late Joiner needs current state? No --> Events only (0 bytes) Yes --> Q3 Q3: Continuous change? (position/rotation) Yes --> Continuous sync No --> Manual sync (minimal [UdonSynced])

SDK Versions

Note: SDK < 3.9.0 was deprecated on December 2, 2025. New world uploads require 3.9.0+.

Official Resources

Issues are welcome -- bug reports and knowledge requests help improve this project.

Pull Requests are not accepted -- all fixes and updates are made by the maintainer.

This project is not affiliated with VRChat Inc. No official endorsement, partnership, or association is implied.

"VRChat", "UdonSharp",

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