# Reported issues for Loomle MCP for Unreal

Pod holds 20 of 42 problems reported by people outside the maintainer team. Issues filed by the project's own owners, members and collaborators are excluded entirely — a maintainer's release checklist is not a warning to a prospective user.

Back to [Loomle MCP for Unreal](/mcp/loomle-mcp-for-unreal).

## Most discussed

### Graph dry-run crashes Unreal Editor when connecting pins on nodes added in the same patch

## Summary

A Graph Domain `patch ... dry run` can crash Unreal Editor when the same ordered patch adds contextual palette nodes and then connects/disconnects pins involving those newly added aliases.

The MCP call loses its runtime connection and Unreal terminates on an `UEdGraphPin::GetOwningNode()` assertion. Because this is a dry run, it should return either a valid plan or a diagnostic and must not crash the editor.

## Environment

- Loomle Client / Bridge: 0.7.4
- Protocol: 4
- Unreal Eng

[Read the thread](https://github.com/loomle/loomle/issues/185) · 2026-08-07 · closed · outside contributor · 3 comments

### blueprint_graph_edit cannot reliably build Actor BP to AnimBP instance variable chain

# blueprint_graph_edit cannot reliably build common AnimBP instance access chain

## Summary

While implementing an Animation Blueprint driven bow string workflow, `blueprint_graph_edit` could not reliably create a common Blueprint graph chain:

```text
SkeletalMeshComponent reference
-> Get Anim Instance
-> Cast to Anim Blueprint generated class
-> Set variable on AnimBP instance
```

This chain is a standard workflow when an Actor Blueprint needs to pass runtime values into an Animation Bluepr

[Read the thread](https://github.com/loomle/loomle/issues/149) · 2026-05-21 · closed · external user · 2 comments

### execute can hard-crash Unreal on invalid package path and returns poor recovery state

## Summary

Calling `mcp__loomle__.execute` with Python code that accidentally passes an invalid Unreal asset package path to `unreal.load_asset()` can hard-crash Unreal Editor. After the editor restarts/reconnects, subsequent `execute` calls may report `Python runtime is not initialized`, while other LOOMLE tools still report the runtime as connected/degraded.

This was triggered during a whole-project AnimBlueprint scan.

## Environment

- Project: `D:/UE/SniperRifle`
- Unreal Engine: `D:/UE_5

[Read the thread](https://github.com/loomle/loomle/issues/144) · 2026-05-20 · closed · external user · 3 comments

### Looking for Unreal MCP and UE agent tooling feedback

I am looking for feedback from developers working on Unreal Engine MCP servers, AI agent tooling, editor automation, Blueprint tooling, PCG workflows, Material graphs, or UMG tools.

LOOMLE is an MCP tool for operating live Unreal Engine projects through UE-semantic tools rather than raw scripts first. The current focus is:

- attach to a running Unreal project
- read active editor context and selection
- inspect Blueprint, Material, PCG, and Widget assets
- use UE palettes for node/widget creat

[Read the thread](https://github.com/loomle/loomle/issues/142) · 2026-05-18 · closed · outside contributor · 2 comments

### Promote global loomle client + formalize 'loomle mcp' as the agent runtime entrypoint

## Summary

LOOMLE should stop depending on Codex-managed MCP configuration and instead treat the globally installed `loomle` CLI as the stable agent entrypoint.

In this model:

- `loomle` is a client/launcher, not an MCP server
- `loomle` discovers the current UE project and runtime
- `loomle` connects to the project/runtime MCP server on behalf of the agent
- the agent executes `loomle` under the host approval model instead of trying to mutate Codex MCP session/config state

This issue also f

[Read the thread](https://github.com/loomle/loomle/issues/133) · 2026-03-26 · closed · outside contributor · 2 comments

### [Bug] Windows install has bootstrap EOF and update extraction path error (os error 123)

# [Bug] Windows install path has two failures: bootstrap EOF and update extract error `bundle\\mcp\\client\\:`

## Summary
On Windows, installing/updating LOOMLE in `D:\UE\VR_Codex` hit two separate failures:
1. bootstrap script failed with transport EOF (`0 bytes from transport stream`), and
2. `loomle update --apply` failed with an extraction path error:
   `failed to create extracted file ...\\bundle\\mcp\\client\\: 文件名、目录名或卷标语法不正确。 (os error 123)`

Manual fallback (downloading installer and 

[Read the thread](https://github.com/loomle/loomle/issues/115) · 2026-03-18 · closed · external user · 2 comments

### moveNode reports success but Blueprint nodes do not visibly move; coordinates/width not observable

## Summary
In UE 5.7 + loomle-mcp-server v0.2.10, `graph.mutate` reports successful `moveNode` operations (`changed=true`), but selected Blueprint nodes do not visibly move in the Blueprint editor. This blocks agent-driven layout operations.

## Environment
- OS: Windows
- UE: 5.7.3
- Project: `D:\UE\DRAVIAN`
- Asset: `/Game/Environments/BluePrints/BP_SplineExcluder.BP_SplineExcluder`
- Graph: `UserConstructionScript`
- Loomle MCP: `v0.2.10`

## Reproduction
1. Open Blueprint editor for `BP_Spli

[Read the thread](https://github.com/loomle/loomle/issues/44) · 2026-03-13 · closed · external user · 3 comments

### [Proposal] UE Editor Error Ingestion Channel for Agent (Fast + Reliable)

# [Proposal] UE Editor Error Ingestion Channel for Agent (Fast + Reliable)

## Background
Current UE-side errors come from multiple sources (runtime logs, Blueprint compile, build/hot-reload, PIE/test, asset load failures).
For agent workflows, we need one unified channel that is low-latency and does not lose critical events when real-time transport is unavailable.

## Goal
Build a lightweight error ingestion pipeline that:
- Normalizes multi-source UE errors into one schema.
- Streams real-time

[Read the thread](https://github.com/loomle/loomle/issues/23) · 2026-03-12 · closed · outside contributor · 3 comments

## Most recent

### [0.7.12] SAL Graph dry-run crashes Unreal in MaterializeDefinition / SetGivenSelfScope

## Summary

`patch <graph> dry run` can crash Unreal Editor while materializing a Blueprint `UK2Node_CallFunction`. I reproduced the same access violation twice, first with Loomle Bridge 0.7.10 and again after upgrading to 0.7.12.

The MCP client only receives `runtime.connection_closed`; the Editor process terminates and UE writes a crash dump.

## Environment

- Unreal Engine 5.7.4
- Windows 11 25H2
- Loomle Bridge 0.7.10 (first crash)
- Loomle Bridge 0.7.12 / protocol v5 (second crash)
- Grap

[Read the thread](https://github.com/loomle/loomle/issues/195) · 2026-08-17 · open · outside contributor · 0 comments

### Add a resident use-unreal-python safety workflow Agent Skill

## Summary

Add a resident Loomle Agent Skill for safely using the unrestricted Unreal Python fallback, tentatively named:

`use-unreal-python`

The Skill should guide an agent through capability selection, API discovery, idempotent script design, continuation polling, post-failure recovery, explicit persistence, and result verification.

This should be workflow policy only. It should not grant a new Unreal capability or replace the structured SAL interfaces.

## Motivation

Loomle's new `python

[Read the thread](https://github.com/loomle/loomle/issues/193) · 2026-08-09 · open · outside contributor · 0 comments

### [0.7.6] Creation-only Graph dry run crashes UWidgetBlueprint sandbox in UObjectAnnotation cleanup

## Summary

A Graph-domain dry run that only creates one contextual function-call node crashes Unreal Editor while Loomle builds the Blueprint sandbox.

This is different from #185: there are no connect, disconnect, default-value writes, creation-alias pin references, or ordered graph mutations. The assertion occurs while duplicating and compiling the UWidgetBlueprint sandbox, then purging duplicated objects.

## Environment

- Loomle Client: 0.7.6
- Loomle Bridge: 0.7.6
- Protocol: 4
- Unreal E

[Read the thread](https://github.com/loomle/loomle/issues/189) · 2026-08-08 · closed · outside contributor · 1 comment

### status reports RUNTIME_BUSY while runtime accepts asset RPCs

## Summary

After updating to Loomle 0.6.20 and restarting the Unreal project, `loomle.status` can keep reporting `RUNTIME_BUSY` / `degraded` even though normal asset RPCs work immediately afterwards.

## Environment

- Loomle CLI / MCP: 0.6.20
- Project: Unreal Engine 5.7 project on macOS
- Editor state: editor window fully open and interactive, not in PIE

## Observed behavior

`mcp__loomle.status` returned:

```json
{
  "status": "degraded",
  "message": "Loomle runtime is degraded.",
  "issu

[Read the thread](https://github.com/loomle/loomle/issues/180) · 2026-06-05 · closed · outside contributor · 1 comment

### Tool names with dots fail Claude desktop MCP validation (e.g. graph.list)

Claude desktop (v1.9659.2) rejects Loomle MCP tools with this error:

tools.10.FrontendRemoteMcpToolDefinition.name: String should match pattern '^[a-zA-Z0-9_-]{1,64}$'

Tool names like graph.list, graph.query, graph.mutate contain dots which 
Claude desktop's MCP validator does not allow. The hammer icon never appears.

Fix: rename tools using underscores (graph_list, graph_query, graph_mutate).

Loomle v0.6.10, Windows, UE5.7, CRS project.

[Read the thread](https://github.com/loomle/loomle/issues/168) · 2026-06-01 · closed · external user · 1 comment

### Add UserDefinedStruct inspect/create/edit support

## Summary

Loomle currently supports asset-level work for Blueprint, enum, Material, PCG graph, and WidgetBlueprint, but does not appear to expose equivalent support for Blueprint UserDefinedStruct assets.

This is a practical gap when working on Blueprint-facing data contracts or UI data models.

## Requested Capability

Add support for UserDefinedStruct assets, similar to enum support.

Possible tool coverage:

- `asset_create` with `kind: "userDefinedStruct"`
- `asset_inspect` with `kind: "u

[Read the thread](https://github.com/loomle/loomle/issues/166) · 2026-05-29 · closed · outside contributor · 1 comment

### Expand context tool with reliable Blueprint editor selection details

## Summary

The existing `context` tool is useful, but Blueprint editing workflows need richer and more reliable active-editor selection details.

When a user says “look at the selected node”, Loomle should be able to resolve the current Blueprint editor, active graph, selected nodes, and selected pins into stable references that can be passed directly to later inspect/edit tools.

## Proposed Extension

Extend the existing `context` tool rather than adding a separate selection tool.

Example re

[Read the thread](https://github.com/loomle/loomle/issues/164) · 2026-05-29 · closed · outside contributor · 1 comment

### Parallel blueprint_compile calls can fail with runtime RPC connection closed

## Summary

Running two `blueprint_compile` calls in parallel through `multi_tool_use.parallel` caused one compile to succeed and the other to fail with `runtime RPC connection closed`.

## Environment

- LOOMLE version: 0.5.22
- Unreal project: `D:/UE/SniperRifle`
- Active world: `/Game/OurBowIntegration/Maps/FastPersonBow_Our`
- Assets:
  - `/Game/UltimateBowSystem/Demo/Blueprint/BP_BowSystemSampleCharacter`
  - `/Game/OurBowIntegration/Blueprints/BP_OurBowCharacter_FromSample`

## Repro Steps

[Read the thread](https://github.com/loomle/loomle/issues/152) · 2026-05-22 · closed · external user · 1 comment

### blueprint_graph_edit addNode recipes mismatch palette schema and dry-run misses function failure

# blueprint_graph_edit addNode schema mismatch and misleading dry-run

## Summary

`blueprint_palette` returns add-node recipes that `blueprint_graph_edit` cannot execute as-is, and `blueprint_graph_edit` dry-run can report success for function node creation that fails during the real operation.

## Environment

- Project: `D:\UE\SniperRifle`
- Asset: `/Game/XRFramework/Blueprints/BP_Bow_02`
- Graph: `BowRelease`
- Tool: LOOMLE MCP `blueprint_palette` and `blueprint_graph_edit`

## Repro 1: pale

[Read the thread](https://github.com/loomle/loomle/issues/148) · 2026-05-21 · closed · external user · 1 comment

### widget_mutate: setProperty cannot write slot properties (LayoutData, Padding, ZOrder, alignment)

## Summary

`widget_mutate`'s `setProperty` op can only write **widget-own properties** (e.g. `Font`, `ColorAndOpacity`, `WidgetStyle`). It cannot write **slot properties** such as `LayoutData`, `ZOrder`, `Padding`, `HorizontalAlignment`, `VerticalAlignment`, etc., even though `widget_describe` correctly reports these as `writable: true` under `slotProperties`.

## Reproduction

```json
{
  "op": "setProperty",
  "args": {
    "name": "PanelBackdrop",
    "property": "LayoutData",
    "value": "

[Read the thread](https://github.com/loomle/loomle/issues/141) · 2026-04-19 · closed · outside contributor · 1 comment

### Feature: UMG Widget Tree primitive for WidgetBlueprint editing

## Problem

Loomle's `graph.*` tools operate on Blueprint **EventGraph** nodes (K2 graph), but UMG `WidgetBlueprint` assets contain a second, entirely separate data structure: the **WidgetTree** (the hierarchy of Slate/UMG widgets built in the UMG Designer panel).

These two structures are unrelated:
- `graph.query` / `graph.mutate` → EventGraph nodes and pins ✅
- WidgetTree (CanvasPanel, ScrollBox, Button, TextBlock hierarchy) → not reachable ❌

Currently there is no way for an agent to read or

[Read the thread](https://github.com/loomle/loomle/issues/139) · 2026-04-18 · closed · outside contributor · 1 comment

### Website install instructions do not match the shipped installer/package on macOS

## Summary

On 2026-03-29 I tried a fresh macOS install in an Unreal project from the canonical instructions on https://loomle.ai/.

I hit three separate mismatches between the website, the installer script, and the shipped `v0.4.1` package:

1. The homepage command uses `sh -s -- install --project-root "$PWD"`, but `install.sh` currently requires Bash syntax and does not accept the `install` positional argument.
2. The installer default latest path resolves to `loomle-latest`, but that release 

[Read the thread](https://github.com/loomle/loomle/issues/134) · 2026-03-29 · closed · outside contributor · 1 comment

The remaining reports are on [the project's issue tracker](https://github.com/loomle/loomle/issues).