As of 2025–2026, the safest and quickest method remains from .zip to .sb3 . No special software, no uploads, no risk. Only attempt manual re-zipping or online tools if the file structure is genuinely broken.

This is the first thing to try. It takes less than 10 seconds.

A dialog box will appear asking if you want to keep .zip or use .sb3 . Click . Method 2: Re-Zipping Assets (For Extracted Folders)

Ultimately, the ability to convert a ZIP to an SB3 is more than a technical parlor trick; it is a profound educational moment. It demystifies file formats for young learners. It teaches them that a file extension is often just a label for the computer's benefit, while the data inside remains the same.

If your .zip archive already contains the root files ( project.json and the assets) directly inside it—without being wrapped in an extra folder—you can change the extension directly. On Windows Open and navigate to your ZIP file.

Select all the files inside your project folder (the json, the images, and the sounds). Right-click and choose Send to > Compressed (zipped) folder .

Search for a reputable online archive converter like CloudConvert or Zamzar. Upload your .zip archive.

SB3 files cannot be encrypted. You must remove the password from the ZIP using tools like 7-Zip (Windows) or Keka (Mac) before converting.

This is the most reliable "updated" method for Windows and Mac users. It doesn't require any third-party software. On Windows:

If you don't have Scratch 3.0 installed on your computer, you can use online conversion tools to convert the ZIP file to SB3. These tools allow you to upload the ZIP file and download the converted SB3 file.

Suppose you have a ZIP file called game.zip that contains a Scratch project. You can use the zip_to_sb3 function in Python to convert it to an SB3 file:

contains these files, you must move the files to the root level of the ZIP for it to work in Scratch. Step 2: Convert via File Renaming

If Scratch doesn’t load the file, ensure project.json is at the root of the ZIP (not inside an extra folder layer).

80% – Works perfectly for pure project files. Fails if the ZIP contains a folder structure (e.g., project/assets/ ).

You may need to convert a ZIP file to SB3 if you have a Scratch project saved as a ZIP file and want to:

Sometimes ZIP files converted back to SB3 don't open because the compression format is wrong or the project.json is corrupted. How it works: