VRChatWorldSDKAgentic

Tooling that lets an AI agent develop VRChat worlds autonomously in Unity 2022.3.22f1 + VRChat Worlds SDK 3.10.5 — organising assets, writing Udon, assembling scenes, verifying behaviour, and building.

Clone it, run one command, and both halves of the MCP surface come up against your project:

node scripts/install.mjs --project "E:/Unity/WorldTest"

No npm install, no second repository to fetch, no editor preferences to set by hand. The generic Unity MCP layer ships in the box.

Two servers, one editor. Ours covers everything VRChat-specific; the bundled one covers the generic Unity surface we deliberately do not reimplement. They share nothing but the editor they attach to.

Why a custom bridge at all: VRChat's build API needs a live SDK control-panel EditorWindow and a pumped EditorApplication.update, so -batchmode -executeMethod cannot drive it — and Unity's own MCP requires Unity 6, which VRChat does not support. See docs/ARCHITECTURE.md.

Status

Complete and verified against a live editor: 167 checks across 12 suites.

node tests/run-all.mjs

The end-to-end run builds the world the plan called for: a button that opens a door, a counter synchronised across players, a video player, a prop you can pick up, and a chair you can sit in. It scaffolds the scene, generates a room with a doorway, places every object and SDK component declaratively, lints four UdonSharp behaviours before Unity sees them, compiles them, wires and verifies their fields reach the backing UdonBehaviours, audits the geometry, renders the scene, checks the budget, proves every interaction in a ClientSim play-mode session — interact, grab, drop, sit, stand, and the video callbacks, 46 scenario steps — parses the telemetry each feature emits, and produces a real .vrcw for both PC and Quest, with no human in the editor.

One tool is not end-to-end verified: verify_multiclient, which launches real VRChat clients to test synchronisation, needs a VRChat client installed and an account signed in. Its preconditions, log parsing and preflight are tested (verify_multiclient_preflight); the launch-and-converge path has never been run here. It reports precisely which preconditions are missing rather than failing opaquely, but treat it as untested code until you have run it yourself.

Three other honest limits. A job interrupted by an editor restart is journalled and reported as interrupted; it does not resume by itself, because a half-finished build or play-mode session has to start again anyway. Scenario steps do not check reachability — grab and interact reach the object wherever it is, so whether a player could actually get to it stays scene_spatial_audit's question. And there is no texture atlasing or LOD generation: budget_report says when atlasing would help and budget_apply_import_presets handles compression, but rewriting meshes and UVs is a destructive operation that deserves a human deciding to run it.

Related MCP server: Union Unity MCP Server

Tools

Bridge and observation — unity_instances, unity_ping, unity_health, unity_methods, unity_harden_editor, unity_editor_state, unity_console, unity_compile_status, unity_refresh_assets, unity_menu_item, unity_eval_csharp, unity_invoke_static, unity_get_static, unity_job_submit/status/list/cancel/wait

Bundled generic layer — companion_status, companion_setup (diagnose and repair it from inside an agent run; its own ~47 tools arrive through the second MCP server)

UdonSharp — udon_lint (no Unity), udon_whitelist_query, udon_syncable, udon_export_whitelist, udon_status, udon_create_script, udon_compile, udon_attach, udon_set_fields, udon_read_vars, udon_list_behaviours

World and scene — world_project_status, world_fix_project, world_scaffold, world_describe_scene, world_validate, scene_apply_spec, scene_describe, scene_component_whitelist, scene_spatial_audit, scene_survey_shots, geo_generate, geo_kinds

Verification and build — verify_scenario_schema, verify_clientsim (18 scenario step types: wait, interact, send_event, set_var, grab, drop, sit, stand, teleport, respawn, and assertions on variables, active state, position, held state, station occupancy and the console), verify_build_local, verify_multiclient_preflight, verify_multiclient, verify_vrc_logs, verify_udon_exceptions, world_build_status, world_set_dry_run, world_switch_platform

Budget and assets — budget_report, budget_snapshot, budget_diff, budget_import_audit, budget_apply_import_presets, assets_inventory, assets_unused, assets_make_material, assets_import_file, assets_ledger, open_assets_sources, open_assets_search, open_assets_files, open_assets_fetch

Safety — project_status, project_checkpoint, project_checkpoints, project_rollback

Upload is deliberately absent. The autonomy boundary is local Build & Test, so BuildAndUpload and the publish APIs are not exposed at all rather than merely discouraged.

Install

node scripts/install.mjs --project "E:/Unity/WorldTest"

It links com.agentic.vrcw and the bundled com.coplaydev.unity-mcp into the project, checks the committed bundles, builds the linter if dotnet is present, runs uv sync for the bundled Python server, and writes .mcp.json with both servers — the generic one with telemetry switched off. Every step is idempotent and reports itself, so re-running it is also how you diagnose a setup.

Then check which Unity installs may open the project, and run the supervisor:

node bundled/vrcw-supervisor.mjs editors --project "E:/Unity/WorldTest"
node bundled/vrcw-supervisor.mjs watch --project "E:/Unity/WorldTest" --auto-dismiss-dialogs true

editors exists because several installs can claim the same version string while only one is the build VRChat supports — the Unity China (...f1c1) builds are rejected. --auto-dismiss-dialogs lets the supervisor answer allowlisted blocking prompts; without it a modal dialog stalls an unattended run indefinitely.

One-time human step

Sign in once in the SDK control panel of that Unity project. The panel only registers builders while APIUser.IsLoggedIn, so even local Build & Test needs it. Credentials land in EditorPrefs via SecurePlayerPrefs; the agent never handles a password or 2FA code.

If the generic half goes quiet

companion_status says why, in terms of the four things that actually go wrong: Unity only rescans Packages/ at startup, so a package added to a running editor never compiles until PackageManager.Client.Resolve() runs; the companion's bridge is gated behind an EditorPref that defaults to false; that bridge does not survive a domain reload, so something has to start it again after every recompile; and the status file it leaves behind outlives the editor, so a machine restart leaves a file advertising a port nothing is listening on. companion_setup fixes the first two on demand, the bridge handles the third on every load, and serving comes from connecting to the port rather than from the file — which is why a freshly opened editor, or a freshly rebooted machine, needs nothing.

Development

npm install            # only for building; a clone runs from bundled/ without it
npm run build          # packages/*/dist
npm run bundle         # refresh the committed bundled/ artifacts
npm test               # every suite

Distribution, when you want it elsewhere:

node scripts/make-vpm-listing.mjs --base-url https://your.host/vpm   # Creator Companion listing + zip
node scripts/publish.mjs --dry-run                                   # npm, dry by default
node scripts/update-vendored.mjs --tag v10.3.0                       # refresh the bundled generic layer

update-vendored.mjs refuses to vendor a tag that is not still under a licence permitting redistribution, and tests/companion-mcp.mjs fails if the upstream tools we rely on are renamed.

Layout

• skills/ — agent knowledge packs (vrcw-udon, vrcw-world), grounded in the SDK as verified here

• generated/ — indexes generated from the installed SDK, so they cannot drift (udon-whitelist.json: 35,333 nodes, 133 events, 783 types)

• tests/ — acceptance suites that drive a live editor

• scripts/ — install, bundle, vendor refresh, distribution

• third_party/unity-mcp/VENDORED.md — what is vendored, from which tag, under which licence, and why

• docs/ARCHITECTURE.md — why the design is shaped this way, and the SDK constraints behind each decision

Notes

• The bridge compiles and runs arbitrary C# in the editor. It binds 127.0.0.1 only and requires a per-session token; treat that token as a local credential.

• <project>/.agentic/ holds bridge state: console JSONL, compile diagnostics, job journal, budget snapshots, asset ledger, renders, supervisor status, editor log.

• Regenerate the Udon whitelist after an SDK upgrade: udon_export_whitelist.

• The bundled generic package also starts a server of its own on load (127.0.0.1:8080 by default) — that is its behaviour, not ours; the telemetry opt-out covers it because the editor passes it down.

Local configuration

The installer generates .mcp.json with paths for your machine; this file is intentionally ignored by Git. See .mcp.example.json for the configuration shape. Run scripts/install.mjs --project <project-path> to generate the real configuration, or copy the example and replace /absolute/path/to/VRChatWorldSDKAgentic with your checkout path. Never commit local credentials or the project's .agentic/ runtime state.

License

Original project code is licensed under the MIT License. Vendored MCP for Unity retains its upstream MIT license. The committed Node bundles include third-party code; the applicable copyright notices and license texts are collected in bundled/THIRD_PARTY_NOTICES.txt. Unity and the VRChat Worlds SDK must be installed separately and are not redistributed by this repository.