Loomle MCP for Unreal MCP Server

Loomle

Loomle is an agent-native Unreal Engine integration for reading and changing complex editor objects through SAL, the Structured Agent Language.

SAL turns Blueprint graphs, Widget trees, Class reflection, Assets, and other non-text UE state into compact, ordered text that both people and agents can read, copy, discuss, and patch. It stays faithful to UE: native paths, types, field names, values, palette actions, compiler diagnostics, and editor semantics remain native instead of being replaced by a parallel JSON model.

Why Loomle

Text code already gives agents precise search, references, diffs, and edits. Unreal assets do not. Loomle supplies that missing text workflow while keeping the editor and UE APIs as the source of truth.

• Compact SAL Object Text uses fewer tokens than large generic JSON payloads.
• Queries start with summaries and local views instead of downloading an entire graph.
• Target-relative stable identity paths make returned Nodes, Pins, Graphs, Widgets, and Blueprint objects safe to follow up without kind namespaces.
• Palette and dynamic schema discovery let agents use capabilities that UE actually exposes instead of guessing constructors or fields.
• Dry runs share the real parse, resolve, validate, and plan path before any mutation is applied.
• Native compiler and object health diagnostics stay adjacent to the objects they describe.

Current 0.7 Interface

The standalone Client exposes eight MCP tools:

• status: inspect the Client version, update availability, and bound session and Bridge health.
• project: inspect project availability and bind this MCP session to one Unreal project.
• sal_query: execute one self-contained SAL Query Text.
• sal_patch: execute one ordered SAL Patch Text.
• sal_schema: discover the resident SAL guide and the active interface cards.
• agent_skill: discover and load MCP-managed Loomle workflow Skills without a separate agent-specific installation.
• editor: observe the current Unreal interaction with empty arguments, or open, focus, and close an exact Blueprint or Graph from canonical SAL Target Text.
• python: run unrestricted Unreal Editor Python only as a fallback for capabilities not covered by a structured Loomle interface, and poll an execution only when the initial result supplies a continuation.

The current public SAL modules are Asset, Blueprint, Class, Graph, StateTree, and Widget. They cover Asset Registry discovery, Blueprint declarations and components, Class reflection and defaults, graph-local flow and mutation, StateTree hierarchy and bindings, Widget trees, factual reference queries, compilation, save, and editor context.

Example:

door = target {
  domain: blueprint,
  asset: "/Game/Blueprints/BP_Door.BP_Door"
}

query door
summary

Use sal_schema({}) for the active module index and sal_schema({ module: "graph" }) for one exact interface card. Supported exact reads and Palette Entries provide dynamic discovery with with schema; each interface card states the exact subjects that accept it.

Install

The latest stable Loomle release is available from GitHub Releases for Unreal Engine 5.7 and 5.8. Choose the package matching the installed engine version:

These stable filenames always resolve through the latest final GitHub Release. That release also retains immutable, versioned copies of both archives.

The Fab listing provides the current marketplace-approved Loomle build. GitHub Releases may be newer while a Fab update is under review.

The complete archive contains both native targets and their matching Clients:

LoomleBridge/
  Source/
  Resources/
    Loomle/
      <platform-arch>/
        loomle(.exe)

The executable under Resources/Loomle is the self-contained SAL Client. It requires no separate Python, uv, Node.js, global Loomle install, or project-local Client.

Before upgrading from 0.6, close Unreal Editor and remove or move the old <Project>/Plugins/LoomleBridge directory. A same-named project plugin takes precedence over the new engine plugin and would keep loading 0.6.

Extract the complete archive, then copy the LoomleBridge directory to:

<UE_5.7-or-5.8>/Engine/Plugins/Marketplace/LoomleBridge

Enable LoomleBridge, restart Unreal Editor, and configure an MCP server named loomle to launch the bundled Client with the argument mcp:

macOS:   LoomleBridge/Resources/Loomle/darwin-arm64/loomle
Windows: LoomleBridge/Resources/Loomle/win32-x64/loomle.exe

Full instructions: https://loomle.ai/install.html

Quickstart

1. Open an Unreal project with LoomleBridge enabled.
2. Restart Codex, Claude, or the relevant MCP host after configuring Loomle.
3. Call status once to inspect Client, update, session, and Bridge health.
4. If the session is unbound, call project to inspect or bind the intended project.
5. Call editor({}) to begin from the user's current editor state; use editor({ operation: "open" | "close", target }) for exact Blueprint or Graph presentation control.
6. Use sal_schema when the target module or exact operation is unfamiliar.
7. Inspect with sal_query, dry-run changes with sal_patch, then apply and finalize through the owning asset.

See https://loomle.ai/quickstart.html for a complete first query and patch.

Architecture

Agent / MCP host
  -> bundled Loomle Client (stdio MCP + SAL)
  -> local runtime record
  -> LoomleBridge inside Unreal Editor
  -> UE 5.7 or 5.8 editor APIs and object model

The Client discovers live Bridge instances through ~/.loomle/state/runtimes. This directory is runtime discovery state, not a global installation. Each MCP session keeps one sticky project binding and validates that project's current Editor with a short live health probe. If the bound project is offline, Loomle reports that state and never falls through to another online project. Use project({}) to inspect candidates and bind or switch explicitly when needed.

Development

The repository has four current product boundaries:

• sal/: language parser, normalized model, schemas, and TypeScript SDK.
• interfaces/: resident guide and static UE interface cards.
• client/: standalone MCP Client.
• engine/LoomleBridge/: Unreal Editor plugin.

Install workspace dependencies and run the TypeScript test suite:

npm install
npm test

Build and test the native Client for the current supported runner:

npm run build:executable
npm run test:executable

Run the complete Loomle UE Automation category against a same-commit development plugin compiled with the native tests:

npm run test:ue-automation -- \
  --ue-root <UE-root> \
  --project-template tests/fixtures/ue/LoomleTestHost \
  --plugin-dir <compiled-same-commit-test-plugin> \
  --output-dir <new-artifact-directory> \
  --target darwin-arm64

The output directory must not already exist. Raw plugin source is not a runnable candidate. The final release archive intentionally excludes native test code, so it is not the complete Automation candidate.

Run the small packaged Client-to-UE workflow against the exact audited release archive and its bundled Client:

npm run test:packaged-e2e -- \
  --ue-root <UE-root> \
  --project-template tests/fixtures/ue/LoomleTestHost \
  --plugin-archive <final-release-candidate.zip> \
  --output-dir <new-artifact-directory> \
  --target darwin-arm64

Release assembly consumes only the canonical program at .tmp/client/<platform-arch>/loomle(.exe) and combines it with the Bridge source plugin. See packaging/client/ and packaging/fab/ for the artifact contracts.

Documentation

• Website: https://loomle.ai/
• Install: https://loomle.ai/install.html
• Quickstart: https://loomle.ai/quickstart.html
• Interface overview: https://loomle.ai/tools/
• Releases: https://github.com/loomle/loomle/releases

Repository and product design documents live under docs/; canonical SAL and UE interface contracts live under sal/docs/ and interfaces/. Loomle 0.6 source and documents remain available from the 0.6 branch, its release tags, and repository history; main contains only the current design and code.

License

Loomle is open source under the MIT License. See LICENSE.