Grimoire — UE5 Context Bridge

Read-only MCP server that gives Claude live access to your UE5 project state — Blueprints, interfaces, variables, functions, event graphs, materials, structs, and Data Assets.

Claude → MCP Server (stdio) → IPC Bridge (TCP) → Unreal Host (in editor)

• MCP Server: Exposes tools to Claude, routes requests over TCP

• Unreal Host: Runs inside UE5 editor, executes queries via Unreal Python API

What This Unlocks

Grimoire gives Claude live read access to your UE5 project. Combined with other MCP servers, this enables workflows that weren't previously possible:

• Grimoire + Notion — Claude reads your Blueprint architecture live and writes design summaries, task cards, or system documentation directly into Notion

• Grimoire + GitHub — Claude inspects your Blueprint systems and opens issues, updates wikis, or writes PR descriptions grounded in actual code

• Grimoire + Slack — Claude reads a Blueprint and posts a technical summary to your team channel

• Grimoire alone — Claude reasons about your systems in context, catches bugs, suggests refactors, and answers architecture questions without you describing anything

The pattern is: Grimoire provides the UE5 context, other MCP servers act on it.

Prerequisites

• Python 3.10+

• UE5 project with Python Script Plugin enabled

• Json Blueprint Utilities plugin enabled (built-in, free, Epic Games)

• Claude Desktop or another MCP client

Installation

1. Install Python dependencies

pip install -r requirements.txt

2. Configure the project

Copy the example config and set your UE5 project path (the folder containing your .uproject file):

cp config.toml.example config.toml

On Windows (PowerShell): Copy-Item config.toml.example config.toml

Edit config.toml and set root under [project]. config.toml is gitignored — keep your real paths local only. See config.toml.example for all available keys.

3. Install the Unreal Host

The editor must be able to import ue5_host on its Python path. Two common approaches:

• Copy — Copy the entire ue5_host folder into your project (e.g. paste it at YourProject/Content/Python/ue5_host/). No symlink required; this is the simplest option on Windows.

• Symlink — Point Content/Python/ue5_host at a single checkout elsewhere if you prefer not to duplicate files.

Target layout inside your UE5 project:

YourProject/
└── Content/
    └── Python/
        └── ue5_host/
            ├── ue5_host.py
            ├── handlers.py
            └── __init__.py

You can also skip copy/symlink and pass a full absolute path to the startup script instead (see step 4).

4. Enable the Host in UE5

• Open your UE5 project

• Edit → Project Settings → Plugins → Python

• Under Startup Scripts, add: ue5_host.ue5_host

  • Or the full path, e.g. C:/path/to/grimoire-ue5/ue5_host/ue5_host

• Restart the editor (or run the script manually once)

5. Register the MCP Server with Claude Desktop

Edit your Claude Desktop config (%APPDATA%\Claude\claude_desktop_config.json on Windows):

{
  "mcpServers": {
    "ue5-context": {
      "command": "python",
      "args": ["-m", "ue5_mcp.mcp_server"],
      "cwd": "C:/path/to/grimoire-ue5",
      "env": {
        "UE5_MCP_CONFIG": "C:/path/to/grimoire-ue5/config.toml"
      }
    }
  }
}

Replace cwd and UE5_MCP_CONFIG with your actual paths. Add other MCP servers (Notion, GitHub, Slack etc) to the same config to enable multi-server workflows.

Tools

What Grimoire Can Read

Blueprints

• Parent class — resolved via Asset Registry

• Component hierarchy — full SCS tree

• Variables — names and resolved types (EGait, FInventorySheet, BP_PlayerState_C — not raw ByteProperty)

• Functions — names, typed input/output pins, execution flow body

• Event graphs — bound lifecycle events (ReceiveBeginPlay, ReceiveControllerChanged), custom events, and interface events — with full execution body where traceable

• Warnings — honest flags when data is partially unavailable, with workarounds

Data Assets

• Property values — actual configured data from DA instances (BaseWalkSpeed: 215, SprintMultiplier: 2.85)

• Nested struct values — full property tree with GUID suffixes cleaned

Structs

• Field definitions — all UserDefinedStruct fields with resolved types

• Navigable type system — FInventorySheet → FInventoryContainer → FItemStack fully traversable

Materials

• Scalar parameters — name + default value (HexScale: 50.0, StateBlend: 1.0)

• Vector parameters — name + default RGBA (OpenColor, LockedColor)

• Texture parameters — name + default texture reference

• Output slot connections — which expression feeds EmissiveColor, Opacity etc

• Material function calls — which MF_* functions are used

Cache

• SQLite persistence — parsed data survives across sessions

• Auto-invalidation — dirty flag watchdog marks stale entries every 15 seconds after asset saves, no manual cache clears needed

Execution Body Format

Function and event bodies reconstruct the logical spine of each graph as a readable step list:

call SubscribeToStats_Player
set CachedInvComp
bind_delegate(OnInventorySheetUpdate)
branch
macro:IsValid
dynamiccast
set BP_PlayerState
bind_delegate(OnStatsChanged)
return ValidationResult (SInteractionValidationResults) <- CurrentResult
select (bool) [False, True]

Node types surfaced: call, set, get, branch, macro:Name, bind_delegate(Name), dynamiccast, switchenum, array.op, select, make, break, return X (Type) <- Source

Known Limitations

• Interface implementation list — UE5 Python API does not expose which interfaces a Blueprint implements. Workaround: use query_cache(tool='query_blueprints', has_function='FunctionName') to find implementors by shared function name.

• Branch-aware execution bodies — function bodies are flat step lists; branch true/false paths are not nested. UE5's T3D export does not serialize exec pin connections. For complex branching functions, a Blueprint screenshot helps cross-reference execution paths.

• EventGraph partial traceability — events whose exec chain begins with a macro node (e.g. Switch Has Authority) cannot be fully walked from T3D data. These events surface with an EVENTGRAPH_PARTIAL warning and [exec chain not traceable] body. The event's existence and binding are still reported correctly.

• Deeply nested pure function chains — first-level pure node sources are resolved (<- select, <- GetIsLocked); deeper chains may still show <- ?.

Both the interface list and exec pin connection gaps are known UE5 Python API limitations. An Epic support ticket has been filed requesting exec pin LinkedTo in T3D exports and BlueprintGeneratedClass.interfaces in Python bindings.

How It Works

The UE5 Python API restricts direct access to Blueprint internals. Grimoire uses three alternative pathways:

1. SubobjectDataSubsystem — k2_gather_subobject_data_for_blueprint() + export_text() parsing for components

2. JsonObjectGraphFunctionLibrary.stringify() — for variable names, resolved types (PinSubCategoryObject → actual type name), and Data Asset property values

3. AssetExportTask T3D export — two-pass node graph parsing for function signatures, execution flow, event graphs, macros, delegates, Select nodes, and Material parameters

Requires the Json Blueprint Utilities plugin (built-in, free).

Switching Projects

• Update config.toml: change [project].root and optionally [ipc].port

• For multiple editors: set UE5_MCP_PORT per project (e.g. 65432, 65433)

• Restart Claude Desktop after config changes

Troubleshooting

Editor offline / Connection refused

• Ensure the UE5 editor is open with your project loaded

• Confirm the host started (check Output Log for UE5 Context Bridge: listening on...)

• Verify config.toml port matches the host (default 65432)

Port conflict

• Use a different port in config.toml and set UE5_MCP_PORT in environment

• Or run only one UE5 editor at a time

Timeout

• Increase timeout_sec in config.toml

• Large projects may need more time for asset scans

Python startup script not running

• Check that the Python Script Plugin is enabled

• Use the full absolute path to ue5_host in Startup Scripts if a relative path fails

Cache stale after code changes

• Clear specific entries: DELETE FROM blueprint_cache WHERE asset_path LIKE '%BlueprintName%'

• Cache DB location: YourProject/Saved/Grimoire/cache.db

• The watchdog auto-invalidates on asset save — manual clears only needed after handler code changes

Roadmap

V7 (planned)

• Animation Blueprint anim graph support

• Branch-aware body format — pending Epic Python API exposure of exec pin connections

• Multi-project switching without config changes

• grimoire_setup.py — automated install and config generation

License & contributing

Grimoire is dual-licensed. AGPL-3.0 applies by default; see LICENSE for the full text and DUAL_LICENSE.md for commercial licensing.

Contributions, issues, and PR expectations: CONTRIBUTING.md.