An SB3 file is a project created with Scratch 3.0, a program development platform created at the Massachusetts Institute of Technology (MIT). It contains a program written in Scratch programming language, which is used for creating stories, small games, and animations. SB3 files replaced Scratch .SB2 files.

SB3 file open in MIT Scratch 3.0 SB3 files are saved in the Scratch 3.0 file format. SB2 files are saved in the Scratch 2.0 file format and .SB files are saved in the original Scratch file format. The SB3 file is simply a .ZIP archive that stores contents such as sprites, scripts, costumes, and sound files. To open an SB3 file in the online MIT Scratch editor: Open the "Scratch Project Editor" on the MIT Scratch webpage. Select File → Upload from your computer in the browser window. To create an SB3 file in the online MIT Scratch editor: Open the "Scratch Project Editor" on the MIT Scratch page. Create your project and select File → Download to your computer. Name your file, choose the save location, and click Save. While SB3 files are typically opened and created in the online MIT Scratch editor, an offline editor for Windows and macOS is also available. Since SB3 files are compressed with Zip compression you can extract the contents of the files with Zip utilities, such as Corel WinZip, 7-Zip, or Apple Archive Utility. Change the .sb3 file extension to .zip and unzip the file with the Zip utility.