Monolith is an Unreal Engine editor plugin that gives AI assistants read and write access to most of an Unreal project through the Model Context Protocol (MCP). It runs as a native C++ plugin inside the editor and works with Claude Code, Cursor, Cline, or any other MCP client on Windows, macOS, and Linux.
Instead of registering each of its roughly 1,400 actions as a separate tool, Monolith uses a namespace-dispatch pattern: each of about 26 domains registers one query tool that takes an action name and parameters, and a discovery tool lists what is available. Listings return only names and one-line descriptions by default, with full parameter schemas fetched on demand, so the assistant spends less of its context window on the tool catalog. Response shaping, fuzzy matching on mistyped actions, and read-only or destructive hints on each tool aim to reduce trial-and-error calls.
Covered domains include Blueprints, Materials, Animation (including Motion Matching and AnimGraph authoring), Niagara (including direct HLSL editing), meshes, UI, AI systems such as Behavior Trees, State Trees, and EQS, the Gameplay Ability System, audio, Level Sequences, INI config, and editor control such as builds, log capture, and Play-In-Editor sessions. A Reflection Intelligence layer answers questions about architectural decisions, repository risk hotspots, C++ reflection edges, and network replication.
Two standalone executables ship with the plugin: a proxy that keeps the AI session alive across editor restarts, and an offline query tool that serves the engine source index, project asset index, and reflection queries without launching the editor. The plugin's HTTP listener is reachable on all network interfaces, so the server can be disabled in editor preferences on untrusted networks.
Features
- Namespace dispatch: about 1,400 actions behind one query tool per domain, plus discovery and self-onboarding guide tools
- Blueprints and Materials: create, query, and edit Blueprints and Materials, including variable-reference census and material compilation
- Animation: AnimGraph authoring, Motion Matching setup with Pose Search databases, state machines, blend spaces, and retargeting
- Niagara: module-stack editing, direct HLSL source editing, and search by parameter, data interface, or material
- Gameplay systems: Behavior Trees, State Trees, EQS, Smart Objects, the Gameplay Ability System, Logic Driver state machines, and ComboGraph combo trees
- Engine source search: an offline index of nearly a million engine symbols, plus C++ lookups for include paths, signatures, deprecations, and class stubs
- Project asset search: full-text search over project assets backed by SQLite
- Reflection Intelligence: decision-record harvesting, repository risk hotspots, C++ reflection queries, and replication inspection for RPCs and replicated classes
- Editor and PIE control: builds with fix hints, log and scene capture, live Play-In-Editor property reads, function calls, input injection, and profiling
- Context-saving responses: field selection and compact output on every action, fuzzy suggestions on dispatch errors, and cursor pagination
- Standalone binaries: a session-preserving MCP proxy and an offline query tool that works without the editor running
