Owned Fab content

The fab category takes content you own on Fab from your library into the project without leaving the conversation: sign in, sync your library, find the item, download it, install it. fab(open_search) opens fab.com's search page at a query.

Searching the catalog with Epic's built-in Fab tools

On UE 5.9 the Fab UE Plugin carries its own toolset, FabToolset, in Unreal's Toolset Registry: the tools Epic's Unreal MCP server and AI Assistant use to search the Fab catalog, find free assets and import listings. ue-mcp extends those tools rather than replacing them, and every one of them stays callable while ue-mcp is enabled.

• fab(list_epic_tools) lists the Fab tools the connected editor has, from the registry and from Epic's Unreal MCP plugin, each with the call that runs it. includeSchemas: true adds each tool's input schema.
• Run a registry tool with epic(call_tool, (tool: "[qualified name]", input: (...))), and an MCP plugin tool with epic(call_mcp_tool, (tool, input)).
• When the editor has none, available is false and note says why: usually the Fab UE Plugin is missing or too old for that engine (fab(status) reports it), or the Toolset Registry is off.

No catalog ue-mcp is generated from has recorded the Fab toolset, so it has no epic_* actions of its own; the same holds for any toolset a launcher plugin or a newer engine adds, and epic(list_toolsets) lists every one of them.

Before you start

Fab's editor plugin is not part of the engine install. The Epic Games Launcher adds it as its own Library item, Fab UE Plugin, which installs into Engine/Plugins/Fab and normally arrives with the engine. If fab(status) answers errorCode: PLUGIN_NOT_AVAILABLE, its note says what is missing: open Unreal Engine > Library in the launcher, find Fab UE Plugin, choose Install to Engine and pick your engine version, then restart the editor. A project that disables Fab gets the same code with the step to enable it.

The owned-content actions (list_owned, download and the job actions) need UE 5.8 or newer.

The flow

1. Sign in. fab(login) opens the Epic account portal. When a session is already active it opens nothing and answers unchanged: true. Poll fab(status) until authenticated is true. The session stays inside the Fab plugin: ue-mcp never accepts, stores or returns a token.
2. Sync your library. fab(sync_library) fetches every page of your owned library and publishes it to the Fab table the Content Browser shows. It returns at once; poll fab(status).librarySync until state is complete (or failed, with a sanitized error). The previous snapshot stays in place until every page has arrived, and a failed sync keeps it.
3. Find the item. fab(list_owned, (query: "rock")) filters your synced library by title. Each row carries listingId (what download takes), availableForThisEditor (whether this editor's engine version and platform are among the item's projectVersions) and the item's own fields.
4. Download it. fab(download, (listingId)) starts a job and returns its jobId. engineVersion and platform default to this editor's; pass them to pick another build, and a mismatch lists the versions the listing offers. Poll fab(download_status, (jobId)) for phase, progress, bytes and speed until state is complete. pause_download, resume_download and cancel_download control it; resuming fetches a fresh signed URL and reuses what was already verified. The default output folder is under the Fab cache; outputDirectory (absolute) puts it elsewhere.
5. Install it. fab(install_pack, (jobId)) copies the verified pack's Content packages into the project at their original paths, so their references hold, and rescans them so they appear in the Content Browser. It checks every file and every collision before copying anything: a different file already at a pack path is refused, an identical one is skipped. Config, plugins, executables and project settings are never installed. The inverse is fab(remove_installation, (jobId)), which removes only the files this job created, and refuses when one was modified, is loaded, or is referenced from outside the pack.

When a step is missing, the next action says which: FAB_NOT_SIGNED_IN before a sign-in, FAB_LIBRARY_NOT_SYNCED before a sync.

Loose source files (fbx, gltf, textures) that you downloaded yourself go through fab(import_file, (source, destination)) instead.

What is checked

Downloads run through the engine's BuildPatchServices with SHA verification of every file. verifyOnly: true checks an existing download with a separate read-only pass that never repairs or deletes, so a corrupt file stays for inspection. Job IDs last for the editor session; after a restart, repeat download with the same listing, version and folder and the verified files are reused. Signed URLs and distribution responses are never written to disk or returned.

UE.MCP.Fab.EndToEnd.SyncDownloadInstall runs this whole flow against a local server standing in for Fab and its CDN: a two-page library sync published to the Fab table, list_owned, a signed download through BuildPatchServices, installation of a real engine package checked in the Asset Registry, and its removal. UE.MCP.Fab.Download.NativeTransferAndInstallation covers pause and resume, idempotent installation, edited-file preservation and corrupt-file detection, and UE.MCP.Fab.Library.Protocol the library response and pagination rules.