Since you are looking for a guide on this topic, you likely have a .zip file that you want to turn into a .sb3 file (the format used by Scratch 3.0).

Here is the important secret: An .sb3 file is actually just a .zip file with a different file extension.

If you have a Zip file that contains the assets of a Scratch project, you do not need a special "converter" tool. You just need to rename it.

Here is the step-by-step guide.

The Problem of Reverse Engineering

If an SB3 is a zip, why do we need a converter? Because the reverse isn't always true. You can’t simply rename any old .zip file to .sb3 and expect Scratch to open it.

Scratch requires a very specific internal structure:

A generic zip—say, a folder of family photos or a downloaded Unity asset pack—will crash Scratch’s parser immediately. This is where the Zip to SB3 Converter becomes essential.

Method 3: Using Online Converters (The Risky Path)

There are websites that claim to convert Zip to Sb3. While convenient, they come with warnings.

How they work: You upload the folder of assets, the server zips it server-side, changes the extension, and sends it back.

The risks:

3. No Compression (Store Mode)

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.