Sandbox Specific Mapping
This page describes a few hidden tricks map makers can use to affect interactions of Sandbox features with the map.
You can use the gmod_allowtools property on any entity in your map to allow only certain tools to affect the entity.
The format for the value is a list of tool class names separated by a single space character. The tool class name is the file name of the tool inside the garrysmod/gamemodes/sandbox/entities/weapons/gmod_tool/tools/ excluding the .lua file extension. It will also work with addons.
For example setting it to the following value:
Will only allow Color, Button, Balloon, Light, Lamp, Dynamite, Thruster and Paint Tools to be used on that entity. This is what the "Color Room" in sandbox does.
Leaving the field empty will disallow all tools from being used on the entity.
This field also affects the "Hold C for Context Menu and right click on the entity" feature.
Similarly you can use gmod_allowphysgun on any entity to prevent the Physics Gun from being able to pick that entity up.
The only possible value here is 0 to disallow Physics Gun from interacting with the entity. Any other value will count as allowed.
To add or edit any of these properties, you must disable the Smart Edit option in your Object Properties and manually add or edit the desired property.
Here's an example - gm_construct's Color Room settings: