A Sheet Sandbox game showing the character sheet alongside with the Sandbox Tools menu

Main Article: Building Character Sheets

The Custom Sheet Sandbox is exactly that-- a trimmed-down "sandbox" for you to test in when creating custom sheets, and is an improvement of the Custom Sheet Editor.

Please Note: You will need to store your custom sheet HTML, CSS, and translation.json-files to your hard drive in order to use this feature. Many character sheet developers use code editors like Notepad++, Visual Studio Code) or Sublime Text 3 to edit these files.

Limitations

Custom Sheet Sandbox games have the following limitations:

You are the only player who can access the sandbox. You can't invite others into your sandbox game.
There is only one page in the game, and there is no way to create additional pages.
There is no Video or Voice chat in the game.
You can only have 15 Custom Sheet Sandboxes at any given time.
This is a Pro subscriber feature only.
The sandbox cannot be made to remember the location of your file or working folder; that's a security limitation on your web browser, and not something Roll20 can change.

Benefits over Custom Sheet Editor

Faster to update game
Enables testing Default Sheet Settings in your sheet.json before submitting to Roll20
If using a Text Editor on your computer to develop the sheet, it removed the constant need from the copy-pasting to update the Custom Sheet Editor

Use

As a Pro user you will notice a new button called "Custom Sheet Sandbox" at the top of the home page once logged in. Additionally you will see a similar button (shown below) in the "My Games" section.

Click the Create New Game button. You'll get a new sandbox game.

You can launch the game right away, or paste in your sheet.json-file if you already have it ready.

Once in the game, you'll see there's a floating box with buttons to upload HTML, CSS, and translation files.

Clicking any of these opens a dialog box to upload the relevant file from your hard drive. As soon as the file finishes uploading, all characters in the game will be updated to the new source file. You no longer need to reload the whole VTT to see changes.

If you have your game settings page open in a second browser window, you can upload a new sheet.json file in that window and, from inside the VTT, you can click "Reload Sheet Default Settings" to have that sheet.json file update, again without reloading.

API

The Custom Game Sandbox does include support for API scripts. Please note, however, that API scripts that interact with elements of the VTT that are disabled (such as other players, pages, etc.) won't work in these games. However, there is an API sandbox for the game, so you can test out sheet-affecting APIs before using or releasing your sheet.