Inside a valid Scratch 3.0 project file, you will always find:
: A collection of .svg , .png , .wav , or .mp3 files. These represent the costumes, backdrops, and sounds used in the project. They are usually named using an MD5 hash of the file content (e.g., b7a7cc....svg ).
The ZIP file might be damaged. Try re-downloading or re-compressing the project.
| | Recommended Method | Time | | :--- | :--- | :--- | | Single file, downloaded from Scratch | Quick Rename (Method 1) | 5 seconds | | ZIP from a forum or backup | Re-Compress (Method 2) | 1 minute | | Batch conversion (100+ files) | Command Line (Method 4) | 2 minutes | | Unknown or corrupted ZIP | Online Converter (Method 3 – TurboWarp) | 30 seconds | | School computer, no admin rights | Scratch Offline Import (Method 3) | 10 seconds | convert zip to sb3 updated
Scratch requires standard ZIP compression. If you used advanced compression algorithms like 7z or RAR and simply renamed the extension to .sb3 , Scratch will throw an error. Ensure that your compression software (like 7-Zip or WinRAR) is specifically set to output the format before changing the extension.
provides a suite of free online tools specifically for SB3 files, including conversion, viewing, editing, merging, splitting, and comparing capabilities. All tools run directly in modern browsers without installation. As of May 2026, FileProInfo maintains updated information about the SB3 file format, making it a reliable resource.
: Click Yes when the warning about changing extensions appears. On macOS Locate your file : Find the .zip file in Finder. Rename : Click the file once, then press Enter . Change extension : Change the ending from .zip to .sb3 . Confirm : Click Use .sb3 in the pop-up dialog box. ⚠️ Important Troubleshooting Inside a valid Scratch 3
When a Scratch project is saved, the platform takes the project’s logic (stored in a JSON file named project.json ) and bundles it alongside all the assets—costumes, backdrops, and sounds. This collection is then zipped up and stamped with the .sb3 extension. This design choice was a significant update from the previous Scratch 2.0 ( .sb2 ) format, moving away from a binary structure to a web-friendly, standard-compliant archive.
For non-technical users or batch operations, web tools are excellent. However, many old converters are now defunct or insecure. Here are the that convert ZIP to SB3 as of 2025:
Ensure you didn't accidentally rename or delete the project.json file while editing. The ZIP file might be damaged
⚠️ 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.
Select inside the folder (Ctrl+A on Windows, Cmd+A on Mac). Do not select the parent folder itself. Right-click on the highlighted files. Compress the files:
Ensure file extensions are visible. Click on the tab at the top, look for the Show/hide section, and check the box for File name extensions . Right-click your ZIP file and select Rename (or press F2 ).
If you want to troubleshoot a specific project that will not load, tell me or what error message Scratch shows , and I can help you fix the file structure. Share public link