BKY File

What are BKY files and how to open them

Are you having problems opening a BKY 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 BKY files.

What is a BKY file?

A .BKY file is an App Inventor Blocks XML file.

App Inventor Blocks XML files store the code logic for an App Inventor project's screens using Google Blockly's blocks‐as‐XML representation. Each screen designed in MIT App Inventor has a matching Blocks XML file: when a project is exported (as an .aia archive), every screen includes a .bky file holding its block program.

These XML files are generated by the Blocks Editor inside MIT App Inventor whenever blocks are created or modified inside a screen. They are not used at runtime in the final Android app; instead they are read by the App Inventor environment when the project is being edited or built. The Automator or creator of the file is MIT App Inventor's Blockly system; the typical consumer is the App Inventor build tools (and the user when editing).

The format is a structured XML document where the top‐level element wraps individual <block> entries. Each <block> entry has attributes including type, id, coordinates (x, y), and optionally inline layout, nested mutations (e.g. for component_event, procedures, etc.), statements ("DO", "IF", etc.), and value fields containing nested blocks. Keywords like COMPONENT_SELECTOR, PROP, instance_name appear inside <field> or <mutation> tags.

Byte-level signatures begin with the ASCII characters "<xml" at the start (offset 0), and the file content contains strings such as BLOCK TYPE, VALUE NAME, INLINE and FALSE which are typical of the XML tags and attributes used by Blockly's block serialization. These signatures help distinguish this format.

How to open BKY files

Important: Different programs may use files with the BKY file extension for different purposes, so unless you are sure which format your BKY 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 24, 2026

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