BSG File

What are BSG files and how to open them

Are you having problems opening a BSG file or are you simply curious about its contents? We're here to explain the properties of these files and provide you with software that can open or handle your BSG files.

What is a BSG file?

A .BSG file is a Besiege Machine file.

Besiege Machine files store the design and configuration of a machine created inside the video game Besiege by Spiderling Studios. Each file captures the structure of a player-built machine - such as the blocks used, their placement, orientation, connection details, and optional mod-specific or skin data - so the machine can be saved, shared, loaded, and run inside the game. Besiege itself writes these files when a player saves a machine for future use.

These files are formatted using XML, making them readable and editable in a text editor. Key sections include global placement information (machine origin position and rotation), a listing of required mods (if any), and detailed entries per block: a block ID, unique GUID, transform data (position, rotation, scale), and additional block-specific settings such as visibility, mass, pinning or custom key mapping. Besiege reads these files to reconstruct the machine in game.

Besiege features versioning in its machine files. Within the XML, attributes like version and bsgVersion mark which format version the machine uses. Older files are typically automatically converted by the game to the newer version when loaded. Community tools leverage this structure: editing by hand, or using mod editors and importers, is common. Users often fix corrupted machine files by editing XML text, correcting malformed or invalid entries.

Besiege Machine files begin with identifiable internal markers: an ASCII signature "PREFABIDS" located at offset zero, and strings such as "WORLD POSITION", "WORLD ROTATION", "POSITIONS", "ROTATIONS", and "KEY MAP" appear elsewhere within the file content. These markers help distinguish the format when inspecting file contents or using pattern-based file type identifiers.

How to open BSG files

Important: Different programs may use files with the BSG file extension for different purposes, so unless you are sure which format your BSG file is, you may need to try a few different programs.

We have not yet verified any programs for Windows that work with this specific file format. If you know one, please use the 'Suggest a program' link below. Thanks!

Last updated: August 25, 2026

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