unity-mcp-server

AnkleBreaker Unity MCP

Build worlds. Coordinate agents. See every action. Connect your AI assistants to scene authoring, running games, multiplayer scenarios, tests, builds and profiling through Model Context Protocol. Built by AnkleBreaker Studio for workflows that span more than one editor and one assistant.

Get started · Watch the demos · Measured improvements · Multiple projects · Tool catalog · Changelog

347 named operations	80 exposed MCP tools	269 advanced tools on demand
Editor, Hub and integrations	Small initial discovery surface	Search a category, fetch one schema, run it

Counts reflect the checked-in definitions; optional tools require their corresponding Unity packages. The advanced proxy also discovers routes advertised by newer plugins.

Watch it build a playable prototype

Neon brick breaker: scene construction, materials, gameplay scripts and visual iteration, with the assistant and Unity visible together.

▶ Open video · 25 seconds · Download MP4 · Village and castle demos

Recorded, accelerated excerpts. The silent videos export the same recordings as the GIFs; their duration is not a build-time benchmark. Media details and example prompts.

Built for demanding Unity workflows

Your workflow	What AnkleBreaker provides
Several projects and agents	Independent request routing, explicit project selection and a fair queue for each editor. Architecture
Multiplayer iteration	MPPM scenario/player controls and parent/virtual-player discovery, plus ParrelSync identity. Workflow and live tests
Work you can inspect	Agent history, named undo for supported actions, queue timings, command errors and the Unity Dashboard. Monitoring
Mixed versions and interrupted calls	Per-editor capability detection, legacy fallback and protected retries when both components support them. Compatibility / Retry contract
A full production toolset	Scene authoring, builds, profiling, packages and optional integrations, with advanced schemas discovered on demand. Tool guide

The combination is the strength: routing, scheduling, multiplayer controls and observable results in one workflow. See choosing a Unity integration for a sourced comparison.

Why choose AnkleBreaker? Each agent keeps its project identity, each editor has its own queue, and supported actions leave a history you can inspect and undo. Advanced tools extend that workflow into multiplayer iteration, Unity Hub and project-specific integrations. Those behaviors have dedicated regression checks and real-editor evidence, not just a feature list.

Get started

Install from source: the commands below install main in both repositories, including the improvements documented here. Published npm packages and version tags may lag behind main.

1. Add the Unity plugin

In Unity, open Window → Package Manager → Add package from git URL:

https://github.com/AnkleBreaker-Studio/unity-mcp-plugin.git#main

The MCP status dropdown appears automatically in Unity's main toolbar. Open the Dashboard from it, Window → AB Unity MCP, or Tools → AnkleBreaker → Unity MCP. Verify the bridge is running there. If you previously hid the indicator, choose Show Toolbar Status. Toolbar and menu access.

2. Install the server

Use Node.js 18 or newer; a maintained Node.js LTS is recommended.

git clone --branch main https://github.com/AnkleBreaker-Studio/unity-mcp-server.git
cd unity-mcp-server
npm ci

3. Connect your assistant

For clients that accept an mcpServers JSON configuration:

{
  "mcpServers": {
    "unity": {
      "command": "node",
      "args": ["C:/path/to/unity-mcp-server/src/index.js"]
    }
  }
}

Use the absolute path to your checkout. On macOS and Linux, use its Unix path. Clients with another configuration format need the same command and arguments. Restart or reconnect the client's MCP session after editing the configuration.

Editor discovery is automatic. Unity Hub is only needed for Hub commands; set UNITY_HUB_PATH if it is installed elsewhere. See all configuration options.

4. Try a complete workflow

List my running Unity projects. Select my prototype, inspect its scene and compilation errors, create a platform, then capture the scene so I can review it.

Find the multiplayer tools. List my MPPM scenarios and the players configured in the selected project.

Inspect the scene's memory use and largest objects, then show me the actions performed by each agent.

From environments to playable levels

A village, built and refined in Unity

Terrain, houses, materials, trees, fences and paths: the assistant constructs a scene and inspects the result as it goes.

▶ Open video · 25 seconds · Download MP4

A castle you can walk through

Multi-room construction, lighting adjustment and a first-person walkthrough in the recorded project.

▶ Open video · 18 seconds · Download MP4

All demonstrations, prompts and media formats →

Multiple projects, multiple agents

Keep an agent on your game, another on a package test project, and use the multiplayer tools to inspect Host/Client scenarios. Project routing and per-agent scheduling are separate responsibilities, so requests retain their destination while waiting for Unity.

1. Call unity_list_instances and identify the project by name and path.
2. Call unity_select_instance with projectName or a discovered port.
3. Include that port on editor calls when coordinating simultaneous tasks.
4. Discover again after an editor restart: ports are dynamic.

Discovery checks the live Unity identity before adopting a port, including registry and default-port fallbacks. Named selection keeps that identity through verification, and stale discovery cannot overwrite a newer project choice. Identity, concurrent selection and compatibility.

{"name":"unity_editor_state","arguments":{"port":7891}}

7891 is an example; use the port returned by discovery. MCP callers can pass _meta.agentId (or the compatible _meta.agent_id) to keep agent selections and queue attribution separate. Each stdio process has its own default identity.

Within an editor, the plugin serializes writes and batches up to five reads per update. Different editor processes have independent queues. Simultaneous agents can still make conflicting edits to the same object, so assign clear ownership for shared scene work.

Explore the editor

Build & edit	Inspect & verify	Extend & coordinate
Scenes, GameObjects, components	Console and compilation errors	Multiplayer Play Mode
Prefabs, materials, ScriptableObjects	EditMode / PlayMode test jobs	ParrelSync instances
Animation curves and controllers	Physics queries, scene statistics	Unity Hub editors and modules
Terrain, navigation, particles	Profiler, memory, Frame Debugger	ProBuilder, UMA, Amplify
UI, audio, input actions	Screenshots and action history	Project-specific context resources

Discover advanced capabilities with unity_list_advanced_tools. Filter by category or search, retrieve the schema for the tool you need, then call it through unity_advanced_tool. Full category guide and examples →

Workflows to try next

Goal	Ask your assistant	What makes it useful
Compare two projects	“List my editors, inspect the package versions and compilation errors in each, then summarize the differences.”	Explicit targets and independent queues.
Iterate on multiplayer	“Find the MPPM tools, inspect the selected scenario and start its configured Host and Client players.”	Native scenario and virtual-player identity. Guide
Validate a change	“Run the selected EditMode tests, wait for the job, then show failures and fetch the detailed results in pages.”	Persistent job IDs, diagnostics and paginated reads. Guide
Review agent work	“Show recent actions by agent and tell me which supported actions can be undone safely.”	Native stack checks and attributed action history. Guide
Find expensive content	“Inspect memory consumers and mesh statistics, then capture the scene for review.”	Inspection without copying geometry buffers just to count it. Guide
Maintain a package	“Compare installed packages, check compilation and inspect my build settings before making changes.”	Package requests yield to editor updates. Guide

These are example prompts, not automatic scripts. Select the intended project first and let the assistant discover the current tool schemas and available packages.

Measured improvements

Recorded workload	Before → after	Why it changed
20 small code-execution calls	15.85 s → 1.01 s	Bounded compiler metadata reuse. Measurement
History repaint with 5,000 retained actions	72.45 ms → 1.80 ms	Draw only visible rows; avoid per-selection native textures. Measurement
Construct 20 results from 10,000 stored tests	14.21 ms → 0.036 ms	Build the requested page instead of every detail record. Measurement

Measurements use separate before/after fixtures and historical baselines on Unity 6000.6.2f1 / Windows. Each linked report states its scope. These results do not measure whole-editor FPS or establish a speed ranking against other MCP products.

Compatibility and validation

The plugin declares Unity 2021.3.18f1+ support. Server and plugin versions advance independently and do not need matching version numbers. Current live validation uses Unity 6000.6.2f1 on Windows; minimum-version C# compilation also passes. Actual older-editor execution is deferred.

263 server tests pass across eight CI configurations (Node 18/20/22/24 on Windows/Linux), and the plugin's registry check covers 338 routes. Real-editor workflows include mixed released/current components, two editors, MPPM Host/Client, ParrelSync and actual script reloads. These checks have different recorded source checkpoints; the delivery summary identifies them and the remaining coverage limits.

Explore the tested workflows and their evidence

Verified workflow	Evidence and limits
Released/current components	All four server-plugin pairs on Node 18 and 22, plus concurrent agents across mixed plugin versions. Version matrix
Multiple editors and reloads	Overlapping calls to two editors, four Play Mode reload configurations and lost-result handling after script reload. Validation record
Multiplayer Play Mode 3.0	Host/Client launch, separate agent routing and shared script recompilation. Multiplayer guide
ParrelSync 1.5.2	Native clone identity, independent agents, Play Mode, shared recompilation, settings persistence and clone restart. Gameplay connections need separate validation. Clone guide
Action History	Bounded observers, grouped refreshes and visible-row drawing with stable filters/selection. Notifications · Window costs and cleanup
History persistence	Retention-aware loading, bounded snapshots and recovery after failed saves/loads. Compatibility and recovery
Agent-session retention	Recent completed identities are bounded; busy agents, polling results and global history remain protected. Limits and validation
Scene and asset editing	Enums, references, prefabs, rejected-write preservation and Scene capture cleanup. Editor workflows
Inline camera images	Explicit camera selection, bounded dimensions, restored render targets and decoded PNG checks with current/released servers. Capture guide
Asset previews	Loading yields to editor updates and other agents; requested sizes and metadata-only options are honored. Preview guide
Mesh inspection	Both object-path names work; all eight UV channels and native triangle counts are read without copying geometry buffers. Metadata guide and measurements
Package Manager	Requests yield between editor updates and remain sequential; list/search/info and local add/remove pass with current and released servers. Package guide
Code results	Valid JSON for non-finite/Unicode values, bounded conversion and HTTP output, and no replay after response failure. Execution guide
HTTP downloads	Bounded response reads, including compressed bodies and older plugins; overflow never repeats a command. Response limits
Request input	Complete HTTP/JSON before dispatch, 8 body readers, 64 MiB reservations and a 30-second upload deadline; server preflight avoids oversized uploads. Input guide
Undo across agents	Native stack checks, explicit cascade handling, accurate Undo/Redo eligibility and identity preserved through script reload. Undo guide
Test Runner	Failure cleanup, native cancellation, retained job details through reload and optional pages for large results. Testing guide · Pagination
Unity 6.6 builds	Five Windows Mono builds verify managed diagnostics and restoration of project settings. Other platforms and IL2CPP remain untested. Build guide
UMA V3.1f1	Asset creation, race changes and recipe renames, with the integration isolated from the core bridge. UMA guide

Run the server's ordinary regression suite:

npm ci
npm test

These tests run the real MCP stdio process against isolated mock bridges. The companion plugin's Unity runner and the server's opt-in live suites are documented with their prerequisites and results in the linked guides. Full evidence and follow-up limits · Final documentation and media checks.

Monitor and troubleshoot

Actual Dashboard capture from a Unity 6.6 validation project. The deliberately long agent/request names exercise layout behavior; displayed counters belong to that test session.

The plugin Dashboard shows queue activity, agent sessions, HTTP activity and recent actions. Agent cards update in place, sections remember their state, and long request text stays readable through tooltips. HTTP counters include input refused before ticket creation, body traffic and domain reloads. Dashboard behavior · HTTP fields and measurements.

Requested editor-window captures preserve keyboard focus, identify ambiguous windows explicitly and bound native image allocations. Docked captures exclude tab chrome; inactive tabs require an explicit temporary-switch option. Owned Windows fixtures verify actual UI Toolkit/IMGUI pixels and Dashboard layouts at 360 and 640 px.

Code execution reuses bounded compiler metadata and reports cache activity in unity_editor_state.codeExecution. A local Unity 6.6 benchmark of twenty small calls fell from 15.85 s to 1.01 s; this measures one workload, not every Unity operation. Execution behavior, measurements and limits.

• No editor found: check the plugin dashboard, console and discovered project path. See connection troubleshooting.
• Slow calls: inspect unity_queue_info, unity_agents_list and unity_agent_log. Ticket status separates queue wait and processing time; queue info also exposes inactive-session retention and evictions. Monitoring fields and measurements →
• Compilation in progress: wait for isCompiling: false, then inspect compilation errors. An empty error list during compilation is inconclusive.
• Tool unavailable: check category switches and optional packages in the dashboard. Advanced route discovery supports newer plugins without expanding the initial tool list.
• Response too large: request smaller read results; inspect the effects before repeating a write. Response budgets and image handling.
• Stopped a request: the server stops waiting and polling; accepted Unity work can still finish. Cancellation behavior.
• Client registry limit: set UNITY_MCP_COMPACT_TOOLS=1. Full parameter documentation remains available through advanced discovery.

Frequently asked questions

Which AI clients can use it? Clients that support spawning an MCP stdio server can connect using the Node command above. Configuration syntax and image/tool support depend on the client; no specific model is required by the bridge.

Do I need every optional Unity package? No. The core bridge works independently of optional integrations. Enable the relevant categories and install the packages needed for your workflow; use advanced discovery to inspect available tools.

Can several assistants work on the same project? Yes. Requests are attributed and scheduled per agent. Assign ownership of shared objects: scheduling does not resolve conflicting design changes.

Can I undo every AI action? Supported Unity writes have named undo groups and history. Filesystem operations, arbitrary code and some deferred workflows have different recovery limits. Inspect the Undo contract before relying on rollback.

Is this already a released upgrade? No. This README documents the modernization branch. Existing server/plugin version numbers remain independent; the installation instructions above select the development preview explicitly.

How does it compare? Start with the sourced comparison: routing, fair scheduling, retry recovery, multiplayer controls, monitoring and tool discovery. The measured gains above compare AnkleBreaker revisions under specific workloads.

Support and license

Support development through GitHub Sponsors or Patreon. Report reproducible issues with the server version, plugin version, Unity version and the affected tool.

Companion Unity plugin · Model Context Protocol · AnkleBreaker Studio

Distributed under the AnkleBreaker Open License v1.0. See LICENSE for the full terms, including attribution and restrictions on reselling the tool. AI client and model usage costs are separate.