.UASSET File Format

Introduction

A UASSET file is a package of Unreal Engine, Epic Games’ game engine. Each asset in an Unreal project, such as a static or skeletal mesh, an animation, a material, a texture, a sound or a Blueprint, is saved as its own .uasset file in the project’s Content folder. Levels use the same package format with the extension .umap.

The format follows the engine’s own object system and changes with each engine version. A project’s assets open in the same or a newer version of the editor. Games usually ship them cooked and bundled into .pak or IoStore container files.

Structure

A package starts with the tag 0x9E2A83C1, stored little-endian as the bytes C1 83 2A 9E, followed by a package summary: the file and engine versions, custom version numbers for engine systems and plugins, the total size of the header, package flags, and the counts and offsets of its tables. The name table lists every string used. The import table lists objects from other packages that this one refers to, and the export table lists the objects it defines, each with the position and size of its serialised data.

In cooked games the export data is often split off into a matching .uexp file, and large blocks such as texture mips into a .ubulk file.

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