Archive.png This article or section documents a feature not included in the current version of Scratch (2.0). It is only useful from a historical perspective.

Single Stepping is a tool in Scratch that runs scripts slower or faster, and performs each block individually. Single Stepping can be accessed through the "Edit" option in the toolbar:

File Toolbar.png

What it Does

By clicking on "Start Single Stepping" it starts the process with the current option. By default it is "Flash Blocks (Slow)". These are all the possible options in can be set it to:

Turbo Speed

In turbo speed, all scripts run as fast as possible. This is very useful for speeding up mathematical projects, however makes features such as graphic effects and clicking on sprites lag quite a bit.

In the Flash Player turbo speed is instead named "Turbo Mode", which is accessed by shift-clicking the Green Flag. "Turbo Mode" can also be accessed by clicking the "Edit," drop down list, then clicking "Turbo Mode," to start "Turbo Mode," up. This is much faster than the Squeak (offline) turbo speed, making projects up to 50 times faster. Turbo speed between the online and offline editors differs greatly.[citation needed]


Just runs all the scripts as they would normally be; it's just like having Single Stepping turned off.

Flash Blocks (fast)

Runs a project at normal speed, however, when a block is active, it turns yellow. This is useful for debugging.

Flash Blocks (slow)

Runs a project extremely slowly, and turns blocks yellow when they are active.

How to Turn On

Before you zoom in, hold ⇧ Shift and press the green flag.


This can be useful for:

  • Speeding up mathematical projects
  • Finding the source of a glitch
  • Finding out exactly how a project works
  • Humor and amusement


Main article: Detecting Turbo Mode

There are simple scripts that can be made that detect if Turbo Speed or Single Stepping is on.