unreal-mcp

# Unreal MCP

You are wired into a live Unreal Editor through the `unreal-mcp` MCP server. The server exposes hundreds of tools across 30+ toolsets (actors, blueprints, materials, Niagara, Sequencer, Control Rigs, GAS, automation tests, Live Coding, and more) registered through Unreal's `ToolsetRegistry`. Use it to inspect and mutate live editor state instead of telling the user to do it manually.

You don't need to memorize tool names. The flow below has you discover them on demand.

## First step every time: discover the tool you need, then dispatch it via `call_tool`

Tool search is on by default, so the MCP server advertises only three meta-tools for the whole session: `list_toolsets`, `describe_toolset`, and `call_tool`. Tool names like `BlueprintTools.create` or `SequencerTools.create_level_sequence` are **not in `tools/list`**. They are dispatched server-side through `call_tool` and never registered as native MCP tools. This is deliberate. It keeps your context window small and the prompt cache warm.

When you start work:

1. Call `list_toolsets` to see what's registered, then `describe_toolset` on the candidate(s) to read their tool schemas. If you already know which toolset you need (the user said "make a Blueprint" → the Blueprint toolset), skip the listing and go straight to `describe_toolset` to confirm the available tools and their signatures.
2. Invoke the tool with `call_tool`: pass `toolset_name`, `tool_name`, and an `arguments` object matching the schema you just read. The result comes back on the same turn. No extra round-trip needed.
3. Top-level dispatch (omitting `toolset_name`) is reserved for tools registered directly on the MCP server and is rejected for `call_tool` itself.

If the meta-tools themselves aren't available (`list_toolsets` errors, or you don't see `unreal-mcp` in your MCP server list at all), the editor or its MCP server is not running. Don't bluff. Ask the user to launch the editor (and run `ModelContextProtocol.StartServer` in the console if auto-start isn't on), or follow `references/setup.md` to wire up a project that has never been configured.

## Safety rules

These exist because every MCP call mutates live editor state and runs on the game thread. Treat them as hard constraints, not suggestions.

- **Save first, then save again.** Tell the user to save the project (or call `AssetTools` save APIs) before any bulk change, and again after. MCP edits are not always undoable, especially across compilation boundaries. Treat anything that touches multiple assets as a destructive operation that needs a recovery point.
- **Wait for compilation.** If C++ or shader compilation is in flight, your tool calls will hang or fail in confusing ways. To rebuild C++ from the running editor, drive `LiveCodingToolset.CompileLiveCoding` and wait on its result instead of asking the user to switch to the IDE. That tool blocks until the compile actually finishes and surfaces MSVC diagnostics.
- **Sequential, never parallel.** Tool calls execute on the game thread, so issuing them in parallel deadlocks or fails. Even when calls look independent, serialize them.
- **Always check the result.** Blueprint compilation, widget creation, material edits: many tools return a status that flips between success and failure with no exception thrown on the wire. Read the response before moving on. Treat anything that isn't an explicit success as a stop.
- **Mind PIE.** Editor-only tools (asset creation in particular) behave differently while Play-in-Editor is active. If a result looks wrong, check whether PIE is running and stop it if so.

## Project skills

A project or plugin can register **Agent Skills**: named bundles of instructions that capture workflow knowledge the agent wouldn't otherwise have (a project's naming conventions, folder layout, required setup steps, or the canonical sequence for a multi-step task). These are separate from the toolsets themselves and are reached through the agent skill toolset (`AgentSkillToolset`), not through `list_toolsets`.

Check for them the same way you discover tools, and do it whenever you start unfamiliar work in a project rather than just once:

1. Call `AgentSkillToolset.ListSkills` (through `call_tool`) to see what skills the project registers. Each entry carries a short description of what it covers and when it applies.
2. If a skill's description looks relevant to what the user asked, call `AgentSkillToolset.GetSkills` on it to load the full instructions, then follow them.
3. If nothing matches, fall back to the tool-discovery flow above.

A relevant project skill's instructions take precedence over your generic defaults: it exists precisely because the project's way of doing something differs from the obvious one. (Authoring or editing these skills is a separate task covered by the `unreal-skill` companion skill below.)

## Reference files

- `references/setup.md`: first-time MCP server setup for a project that has never been configured (`.uproject` plugin entry, auto-start `.ini`, `.mcp.json` generation).
- `references/operations.md`: console commands, settings, and a troubleshooting matrix for when things go wrong (port collision, missing toolsets, hangs, empty docked context).

## Companion skills

- **`create-toolset`**: use when authoring a new toolset or adding tools to an existing one. Covers design principles, C++ and Python conventions, registration, error handling, and testing.
- **`unreal-skill`**: use when creating, updating, or reviewing an Agent Skill. Covers what makes a good skill and how to structure one.