What is the SB file format?
.sb files are associated with the Scratch programming environment - specifically the legacy Scratch 1.x desktop application developed by the MIT Media Lab.
Files with the .sb extension store Scratch projects: a complete application bundle containing all required resources, for example:
- graphics and sprite costumes,
- audio data (sounds and music),
- scripts written in the visual Scratch block language.
Unlike the later .sb2 and .sb3 formats (which are ZIP archives containing a project.json), an .sb file is a binary Squeak/Smalltalk serialized object stream. It begins with an ASCII magic header - ScratchV01 or ScratchV02 - followed by an info block (thumbnail, author, comment) and the main object stream encoding the stage, sprites, scripts, costumes and sounds. Images are stored using run-length and Squeak bitmap encoding; embedded sounds are typically 22.05 kHz WAV-style audio.
What is Scratch? Scratch is a visual block-based programming language following an object-oriented paradigm. It was developed as an educational tool for children by the MIT Media Lab's Lifelong Kindergarten Group. Scratch uses simple drag-and-drop "puzzle piece" blocks to create objects and interactive functions, making it easy to build games, animations and interactive stories.
The .sb format was introduced with Scratch 1.0 in 2007 and last used in Scratch 1.4 (2009). Scratch 2.0 (2013) switched to .sb2 and Scratch 3.0 (2019) to .sb3. The modern online Scratch editor cannot open .sb files directly; the offline Scratch 1.4 application or a converter tool is required.
Security & safety
RISK: LOWA Scratch project is sandboxed educational content with no system-level code, so .sb files are low risk. The realistic cautions: only the offline Scratch 1.4 app or a trusted converter should open them - avoid random "Scratch SB to EXE" sites that bundle adware - and very old projects may rely on features dropped in modern Scratch, so some blocks may not convert cleanly to .sb3.
Format details
in a nutshellPrograms that open SB files
Windows2 apps
Scratch 1.4 (offline)
Free Install the legacy Scratch 1.4 desktop app and open the .sb directly to view, run and edit it.
Scratch (modern, via conversion)
Free Convert the .sb to .sb2/.sb3 first, then open it in the online editor or Scratch Desktop. 
macOS1 app
Scratch 1.4 (offline)
Free Run the legacy Scratch 1.4 app to open the .sb (older macOS; on Apple Silicon use conversion to .sb3 instead). 
Linux1 app
Scratch 1.4 (offline)
Free Available via package managers/Squeak; open the .sb directly. Or convert to .sb3 for the modern editor.
Scratch online editor (after conversion)
Free The current editor opens .sb2/.sb3; convert your .sb up first, then load it. Technical details
deep spec| File structure | Binary Squeak/Smalltalk serialized object stream; not a ZIP archive |
| Magic bytes | ASCII string `ScratchV01` or `ScratchV02` at byte offset 0 |
| Byte order | Big-endian |
| Container layout | Info ObjStream (thumbnail, author, comment) followed by main ObjStream (stage, sprites, scripts, costumes, sounds) |
| Image encoding | Sprite costumes stored as bitmaps with run-length and Squeak PixMap encoding |
| Color depth | Up to 32-bit RGBA for embedded costume bitmaps |
| Audio encoding | WAV-style PCM audio, typically 22.05 kHz, embedded in the object stream |
| Stage canvas size | Fixed 480×360 px (Scratch 1.x standard) |
| MIME type | application/x.scratch.sb (informal); generic fallback is application/octet-stream |
| Security | Unencrypted; all data stored as a plain binary object stream |
| Compression | No file-level compression; individual costume bitmaps may use Squeak run-length encoding internally |
| Developer | MIT Media Lab, Lifelong Kindergarten Group |
| Platform support | Windows, macOS, Linux - via the Scratch 1.4 offline editor |
| Superseded by | .sb2 (Scratch 2.0, 2013) and .sb3 (Scratch 3.0, 2019), both ZIP archives with project.json |
| Released | 2007 (Scratch 1.0) |
| Latest version | Scratch 1.4 (2009) - last version to use the binary .sb format |
| Specification | en.scratch-wiki.info |
SB conversions
Community Q&A
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