Before converting, it helps to understand what happens under the hood. An .sb3 file is structurally identical to a standard .zip file. It contains:
: Your operating system may warn you that changing the extension might make the file unstable. Confirm the change to finalize the conversion. Compatibility and Usage Once the file has been renamed to , it is ready to be used with standard Scratch tools: Loading into Scratch
Scratch will bypass the extension, read the internal project.json , and open your project perfectly. You can then click > Save to your computer to download it as a proper .sb3 file. Troubleshooting Common Errors "Application Error" or "Could not load project" convert zip to sb3 updated
If you're a developer looking to create or export .sb3 files programmatically, the @mbw/sb3 package (available on JSR) provides robust abstractions for working with Scratch project files. This package, which is built and signed on GitHub Actions, works with Bun and Deno, making it a great choice for modern JavaScript/TypeScript projects.
⚠️ Warning: Never upload your Scratch projects to an unknown online converter unless you are comfortable sharing your source code and media assets. Many free tools inject ads or track user data. For school projects with student data, avoid online converters entirely and use Method 1 or 2. Before converting, it helps to understand what happens
Press Enter . A prompt will ask if you are sure you want to change the extension. Click .
Check the box next to . (On Windows 11, click View > Show > File name extensions ). Right-click your ZIP file and select Rename . Change the .zip at the end of the file name to .sb3 . Confirm the change to finalize the conversion
If you have already extracted the ZIP file, you cannot just zip the folder back up and rename it. Scratch will not recognize it because the internal file structure gets shifted. Follow these steps to package it correctly: Open the extracted folder containing your project assets.
Hover over and check File name extensions (On Windows 10, just check the File name extensions box in the View tab). Locate your .zip file. Right-click the file and select Rename (or press F2 ). Change the .zip at the end of the filename to .sb3 .