# Custom Data

Accessed via Custom Data in the Mission Specs dialog or the Campaign Editor.

Attaches arbitrary key-value string pairs to a mission or campaign. Custom data has no built-in effect on gameplay; it is intended to be read by Lua scripts that know to look for specific keys.

## Pre-defined keys

Lua scripts can register expected custom data keys by calling `mn.addDefaultCustomData(key, defaultValue, description)`. When a mission is opened in FRED, any registered key that is not already present in the mission is automatically added with its default value. This ensures the expected entries exist without the mission designer having to create them by hand.

The Description box on the left of the dialog shows the description the script author provided for whichever entry is currently selected. If the selected key is not one registered by a script, the box reads No help text provided.

## Adding an entry

Fill in the Key and Value fields and click Add to create a new entry.

## Editing an entry

Select an entry in the list to load it into the Key and Value fields. Modify the fields as needed and click Update to apply the changes.

## Removing an entry

Select an entry in the list and click Remove to delete it.