Unreal Asset Import and Export

🧠 Brains complement: IF an unreal-engine-skills-manager tool (external MCP) exists in this session, call it with {action: "load", skill: "asset-management"} for UE domain knowledge on this topic — correct APIs, architecture, best practices — and treat it as the rubric for any review / "best practices" question. If no such tool is available (e.g. running under Claude Code or Codex without that MCP), skip this line entirely and proceed with this skill alone — do NOT attempt the call.

Asset Discovery & Management Skill

For static-mesh LOD reimport, lost textures or gray/default surfaces despite a correct component material, read mesh reimport material mappings. The bundled scripts/mesh_material_slots.py exposes explicit section inspection and remapping through the existing engine Python API; no native service rebuild.

🔀 Engine owns general asset ops now. In the Unreal 5.8 consolidation, searching, loading, saving, moving, renaming, duplicating, and deleting assets moved to Unreal's native AssetTools toolset (reach it via call_tool; run describe_toolset for its actions) — or you can drive unreal.EditorAssetLibrary / unreal.AssetRegistryHelpers directly from execute_python_code. The old manage_asset MCP tool is GONE. VibeUE's AssetDiscoveryService was trimmed to only the crash-safe delta the engine doesn't provide:

Kept on AssetDiscoveryService	Purpose
import_asset(src, dest_folder, name) → (path, err)	Import an image, mesh or any importable file (folder + name)
import_texture(src, dest_asset_path)	Same importer, full asset path
export_texture(asset_path, file_path)	Export a texture to disk
get_primary_content_browser_selection() → AssetData or None	Primary Content Browser selection
is_asset_open(asset_path) → bool	Whether an asset is open in an editor

Everything else below (search_assets, list_assets_in_path, move_asset, duplicate_asset, delete_asset, save_asset, get_open_assets, get_asset_referencers, find_asset_by_path, asset_exists, …) was removed from AssetDiscoveryService — use the engine AssetTools toolset or EditorAssetLibrary / the Asset Registry.

Data Assets & Data Tables — no dedicated VibeUE service (issues #451, #452)

There is no DataAssetService / DataTableService. Drive them natively:

import unreal

# --- Data Assets (UPrimaryDataAsset / UDataAsset subclasses) ---
# Create: engine DataAssetTools toolset via call_tool (describe_toolset for the action), OR a factory.
da = unreal.load_asset("/Game/Data/DA_Thing")
val = da.get_editor_property("MyField")          # read
da.set_editor_property("MyField", 42)            # write — works for any UPROPERTY
unreal.EditorAssetLibrary.save_loaded_asset(da)

# --- Data Tables ---
dt = unreal.load_asset("/Game/Data/DT_Items")
names = unreal.DataTableFunctionLibrary.get_data_table_row_names(dt)   # row keys
# Read/write rows with the editor DataTable API:
#   unreal.DataTableFunctionLibrary.evaluate_curve_table_row(...) / get_data_table_column_as_string(dt, "Col")
# Engine DataTableTools (call_tool) covers add/remove/get rows + import/export CSV/JSON.

⚠️ Data Table gotchas (verified, #452): the row key ("Name") is reported as a column by some schema readers — it is the row id, not a data field. Writing a row with the wrong value type can be silently coerced — read the row back to confirm. There is no clear_rows; remove rows individually (engine DataTableTools) or re-import an empty CSV. An empty GameplayTag field serializes as "None".

Critical Rules

⚠️ delete_asset on a REFERENCED asset opens a modal dialog that wedges an unattended editor

EditorAssetLibrary.delete_asset asks "this asset is referenced, force delete?" through a modal window when anything points at the asset (a data asset holding the montage you are replacing, a Blueprint default, a level). Nobody answers it from MCP: the game thread stalls (308 s observed), every later call hangs, and the process has to be force-killed with the files removed from disk. Use the plugin's dialog-free delete instead:

# Refuses when referenced and tells you who:
result = unreal.AssetDiscoveryService.delete_asset_unattended("/Game/Anim/AM_Old", False)
# Delete anyway and null every reference (what the dialog's Force Delete does):
result = unreal.AssetDiscoveryService.delete_asset_unattended("/Game/Anim/AM_Old", True)
if not result.b_success:
    print(result.error_message)     # why it did not happen
    print(result.referencers)       # what pointed at the asset

The call returns an FUnattendedDeleteResult struct — result.b_success, result.referencers, result.error_message — so the reason ALWAYS survives, even on a refusal. (It used to return a bool with out-params, and Python maps a False return to None, which silently dropped the reason; that is fixed.) result.referencers is filled on a refusal AND on a forced delete, so you always see what pointed at the asset. Prefer creating the replacement under a NEW name and repointing references over force-deleting.

Even delete_asset_unattended(path, True) refuses a natively rooted in-memory object — it never prompts. Before deleting, the call does a conservative, non-mutating check: it looks at who holds the asset and refuses ONLY when a native GC root holds it directly — a UGCObjectReferencer, which in an agent session is a Python module-level global that created or loaded the asset earlier this session. That is the one case the engine's own force delete cannot clear, so it would stall on the modal "is in use" dialog (6+ minutes observed). When it refuses, the call returns b_success == False with those roots in result.referencers and an result.error_message explaining it. The fix is what the error says: release the Python globals holding it — del my_var, then unreal.SystemLibrary.collect_garbage() — and retry. Every OTHER in-memory referencer is left to the engine's real force delete, which clears it without prompting: on-disk asset references, the Blueprint-palette node spawners, and transient editor helpers like an anim data controller all delete fine. Read-only package files are also refused before the engine delete path, because Unreal can show a read-only-package prompt even when confirmation is disabled. Clear the filesystem/source-control read-only state explicitly, then retry.

The check never mutates state (it does not null any references before deciding), so a refusal leaves the asset and everything around it exactly as they were — safe to retry after releasing the global.

⚠️ Never delete_asset a Blueprint you loaded or compiled this session

EditorAssetLibrary.delete_asset on a Blueprint (Anim Blueprints especially) that is still loaded — which it is, if you created, compiled or read it earlier in the same script — fails inside ForceDeleteObjects and leaves the package half-deleted and corrupt:

Ensure condition failed: false [ObjectTools.cpp:4045]
Failed to unload all packages during ForceDeleteObjects - these packages are likely corrupt.
Consider restarting the editor, noting which assets remain and then deleting them from the
file system manually: /Game/Path/ABP_Thing

Every later call against that path then times out, and the editor typically has to be killed. The recovery is exactly what the message says — close the editor, delete the .uasset from disk, relaunch (watch for a ZenServer stall on the way back up) — so it costs several minutes.

The rebuild-an-asset pattern, instead of delete-then-create:

• Write to a new name and swap references, or
• Delete the file on disk while the editor is closed, then create it fresh, or
• Edit the existing asset in place (clear the graph, re-add nodes) rather than recreating it.

The same caution applies to any asset currently open in an editor tab or referenced by a loaded level. Non-Blueprint assets you never loaded (textures, meshes written by a factory) delete fine.

⚠️ Out-Params Become Return Values in Python — Never Pass an AssetData Argument

get_primary_content_browser_selection is shaped like bool Func(FAssetData& Out) in C++ and is exposed to Python as () -> AssetData or None. Passing an AssetData argument raises TypeError.

# WRONG - TypeError: takes no arguments (1 given)
asset = unreal.AssetData()
unreal.AssetDiscoveryService.get_primary_content_browser_selection(asset)

# CORRECT - call with no out-arg, check the return for None
asset = unreal.AssetDiscoveryService.get_primary_content_browser_selection()
if asset:
    print(asset.asset_name)

🔀 Where each operation lives now

🔀 ALL open assets / ALL selections / open an asset — use Epic's EditorAppToolset

VibeUE covers the single/primary queries above; the list-all and open operations live on Epic's native EditorToolset.EditorAppToolset (call via call_tool; returns {"returnValue": [...]} of package-path strings). These are NOT Python-bound — they only work through call_tool:

# "Show me all open Blueprints" = Epic GetOpenAssets + a type filter
opens = call_tool("GetOpenAssets", "EditorToolset.EditorAppToolset")["returnValue"]
bps = [p for p in opens if isinstance(unreal.load_asset(p), unreal.Blueprint)]

# "Open the selected asset" = VibeUE primary-selection + Epic OpenEditorForAsset
sel = unreal.AssetDiscoveryService.get_primary_content_browser_selection()
if sel:
    call_tool("OpenEditorForAsset", "EditorToolset.EditorAppToolset",
              {"assetPath": str(sel.package_name)})

🚨 Never list broad paths — a /Game listing can return 30,000+ assets

Listing every asset under /Game returns tens of thousands of entries and floods the conversation. Whether you go through the engine AssetTools toolset or EditorAssetLibrary.list_assets, always narrow first:

• Filter by a specific subfolder (e.g. /Game/Blueprints/HUD), and by class where supported.
• If you only need a count or sample, slice in Python before printing — never print the full array.

⚠️ EditorAssetLibrary Save Methods

There is no save_dirty_assets (AttributeError). The real options: unreal.EditorAssetLibrary.save_asset(path), save_directory(dir), save_loaded_asset(obj), save_loaded_assets([objs]). To save everything dirty, iterate or use the engine AssetTools toolset's save action.

⚠️ EditorAssetLibrary.list_assets Has No Class Filter

unreal.EditorAssetLibrary.list_assets(directory_path, recursive=True, include_folder=False) returns path strings only — there is no asset_class_names or any other class-filter kwarg (TypeError: invalid keyword argument). To list assets of one type, either filter the returned paths in Python (load each and check its class), or query the Asset Registry with a class filter via unreal.AssetRegistryHelpers.get_asset_registry().get_assets(...).

⚠️ UE 5.8 AssetData Property Names

get_primary_content_browser_selection() returns an AssetData. Read it with:

AssetData has no object_path attribute (AttributeError). Build it from package_name + asset_name, or just use str(asset.package_name).