Resources and Prompts

Besides the unreal tool, the server offers the other MCP building blocks. Client support for them varies, and everything the editor can do goes through the tool, so none of this is required.

📖 Resources Read-only context a client can attach.

🧾 Prompts Six guided workflow templates.

⌨️ Completions Suggestions for prompt and resource arguments.

📶 Progress and cancellation For long-running calls.

Both routes advertise the same capabilities at initialize:

{ "tools": {}, "resources": {}, "prompts": {}, "completions": {} }

Server instructions

At initialize, both routes send the same instructions text: the search › describe › execute workflow, how to recover from each kind of error, and path conventions. Most clients inject it into the model's context once per session. On the native route, the Server Instructions plugin setting is appended (⚙️ Configuration).

Resources

URI	Contents	stdio	native
ue://capability/catalog	Bounded summary of the capability catalog. Its revision changes when configure changes what is enabled.	✅	✅
ue://project	Project name (redacted), engine version, content root	✅	✅
ue://state/revisions	Counters for selection, level, asset registry and packages. Pin them in options.expectedRevisions to refuse stale writes.	✅	✅
ue://health	Server health, readiness and diagnostics	✅	✅
ue://automation-bridge	Bridge diagnostics and recent activity	✅	✅
ue://assets	Project assets	✅	—
ue://actors	Actors in the current level	✅	—
ue://editor	PIE status and current level	✅	—
ue://selection	Handles of the selected actors	✅	—

Templates (both routes):

Template	Contents
ue://capability/{capabilityId}	A short record for one capability. For the full contract, use describe.
ue://knowledge/{topic}	Stable Unreal reference notes on a topic
ue://asset/{assetPath}	A normalized handle for the asset at a content path

Every read is capped at 64 KiB, and paths are normalized and redacted.

Note

The four live-state resources (assets, actors, editor, selection) need the editor's game thread. The stdio server fetches them through the bridge. The native server answers resource reads on its socket thread, where it can't wait for the editor, so it doesn't offer them (RESOURCE_UNAVAILABLE). The same information is available on both routes through capabilities such as control_actor.list and inspect.get_editor_state.

Prompts

prompts/list returns six workflow templates. Getting a prompt only returns text messages; it never runs anything. Clients that surface prompts often show them as slash commands.

Prompt	Walks through	Arguments (* required)
🔧 inspect-fix	Inspecting a UObject and correcting one property, one reviewed call at a time	objectPath*, propertyName, newValue
📥 asset-import	Checking the destination, importing from a source you supply, validating the result	destinationPath*, sourceFormat
🏗️ level-build	Creating a working level, building its lighting, saving it	levelPath*
🧩 blueprint-edit	Reading a Blueprint, adding a variable and a component, compiling	blueprintPath*, variableName
✔️ validation	Read-only validation of the project, an asset and the current level	assetPath
🎬 sequence-render	Preparing and running a Movie Render Queue job for a level sequence	sequencePath*, outputFormat

Completions

completion/complete suggests values for prompt arguments and for the three template variables (capabilityId, topic, assetPath). Matches rank prefix first, then substring, subsequence, and single typos. Results are capped at 100 values.

Progress

Send _meta.progressToken with a tools/call, and you receive notifications/progress for that call, driven by the editor's own progress events (imports, builds, renders). The token is echoed exactly as you sent it; without a token, no progress is sent. On the stdio route, progress also extends the call's deadline, 30 seconds at a time.

Cancellation

Both routes honor notifications/cancelled:

The request is…	What happens
Still waiting in the editor's queue	Dropped before it runs
Already running in the editor	Finishes, because editor work can't be interrupted safely. Its reply is discarded.

A session can only cancel its own requests.

Protocol versions

Route	Supported versions
🌐 Native HTTP	2025-11-25 (latest) · 2025-06-18 · 2025-03-26
🧩 stdio	The same three, plus the older 2024-11-05 and 2024-10-07

Both negotiate the highest version the client and server share. On the native route, a request that leaves out the MCP-Protocol-Version header uses the session's negotiated version, and a request that names an unsupported version is refused with HTTP 400. A client stuck on a 2024 protocol version should use the stdio route.

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