An SB3 file is essentially a renamed ZIP archive containing the code (as a project.json file), images, and sounds of a Scratch 3.0 project. Because of this shared structure, converting a ZIP to SB3—or vice versa—is a common task for developers who want to modify assets or fix corrupted project files. Key Conversion Methods
You can convert these files using specialized online tools or simple manual renaming:
Online Dedicated Converters:Tools like ezyZip allow you to extract or package SB3 files directly in your browser. These tools are often preferred because they handle the compression without sending your data to a remote server, ensuring privacy.
Manual Renaming (Power Users):Since SB3 and ZIP are technically the same format, you can often convert them by simply changing the file extension.
ZIP to SB3: Ensure all project files (like project.json) are at the root level of the ZIP, then change the extension from .zip to .sb3.
SB3 to ZIP: Change .sb3 to .zip to open the file with standard decompression software like 7-Zip or WinRAR.
TurboWarp Packager:For those looking to convert Scratch projects into more than just a ZIP, the TurboWarp Packager can turn SB3 files into standalone executable files (.exe), HTML, or even ZIP archives formatted for web embedding. Technical Structure of an SB3 Archive
Understanding what's inside helps prevent errors during manual conversion: Zip To Sb3 Converter
project.json: A text-based file that contains the logic and instructions for all sprites and blocks.
Assets: Costumes (images) and sounds are stored as individual files named after their MD5 checksums (e.g., cd21...png).
Compatibility: Manual edits to the JSON file can sometimes corrupt the project, so it is recommended to keep backups before converting. Quick Comparison of Conversion Options Manual Renaming Online Tools (e.g., ezyZip) TurboWarp Packager Ease of Use Fast, but requires file extension visibility enabled. Very easy; drag-and-drop interface. Best for exporting to other formats. Privacy 100% (Local) High (Browser-based processing) High (Local/Browser) Best For Quick inspections. Non-technical users. Packaging games for distribution. json file inside an SB3 to change project variables? Convert .zip to .sb3? - Discuss Scratch
An interesting "feature" of a Zip to SB3 converter is that it often isn't performing a complex file transformation, but rather a simple extension swap and internal reorganization . This is because Scratch 3.0 files (.sb3) are actually renamed ZIP archives
Here are the most notable features and technical insights regarding these converters: Extension Masking : Since an
file is fundamentally a ZIP archive, the most basic "converter" simply renames the extension to JSON Structure Preservation : Converters ensure that a specific project.json
file is present at the root of the archive. This file acts as the "brain" of the Scratch project, defining all scripts, variables, and links to assets. Asset Management An SB3 file is essentially a renamed ZIP
: When converting from a ZIP to SB3, the tool must verify that all costumes (images) and sounds are correctly referenced. In an
file, these assets are often stored with MD5 hash names (e.g., b7cf...svg
) to prevent duplicates and ensure the Scratch editor can locate them. Browser-Based Processing : Many modern converters, like those found on or tools like SheepTester's HTMLifier
, perform the conversion entirely in your browser using JavaScript. This means your project files are never uploaded to a server, providing a layer of privacy and speed. In-Place Modification
: Some advanced tools allow you to "inject" files into an existing ZIP before converting it to SB3. This is used by power users to add high-resolution assets or custom sounds that might be difficult to import through the standard Scratch interface. SheepTester manually convert a folder into an SB3 file without using an online tool? How can I directly modify a .sb3 file? - Discuss Scratch
Using an online “Zip to Sb3 Converter” carries risks:
project.json (Scratch sanitizes most, but old Scratch 2→3 converters had XSS vectors).Recommendation: Use offline conversion (Python script or local tool). Never upload proprietary or student projects to unknown web converters. FAQs 5
.sb3 → will crash Scratch or fail to load.Converting a ZIP file back to SB3 is not always successful. Here are the common pitfalls:
project.json, the converter will fail. Scratch looks for the JSON at the archive root.project.json and broke a comma or a bracket, the converter might create a file, but Scratch will say "Corrupted project."#, %, or &) in asset names can cause the converter to create an unreadable SB3 file.For developers and power users, the manual right-click method is too slow. There are Command Line Interface (CLI) tools that act as a true Zip to Sb3 converter via automation.
Using Node.js and scratch-sb3-converter:
npm install -g scratch-sb3-converter
# Convert a folder to .sb3
sb3-converter pack ./MyProjectFolder -o MyProject.sb3
# Convert a .sb3 to a folder
sb3-converter unpack MyProject.sb3 -o ./ExtractedFolder
This is the gold standard for modders who want to use Git to track changes in their Scratch projects.
Scratch 3.0 read the ZIP files best when they are stored uncompressed (Compression method: Store). High-quality converters will re-zip your assets using the DEFLATE method correctly, ensuring the file loads instantly in the Scratch editor.
Use this if your file is called project.zip but you know it should be a Scratch project.
.zip file..zip extension and type .sb3.Note: This only works if the file was originally an .sb3 that was incorrectly renamed to .zip. If it is a genuine extracted folder, this will fail.
Converting zip files to SB3 files has several benefits: