---
title: MD libraries: reuse a cue template
summary: Library, ref and parameters: one template with different input values.
section: scripting
kind: guide
status: example
updated: 2026-10-27
tags: ["X4","modding","md","libraries"]
sources: ["https://wiki.egosoft.com/X%20Rebirth%20Wiki/Modding%20support/Mission%20Director%20Guide/"]
---
## What a library is


A `library` defines a cue template; a referencing `cue ref` creates its use. It is not a Lua function. Required parameters have no `default`; the user supplies `param` without a `params` wrapper.



## Complete independent example


```xml
<mdscript name="WikiLibraryDemo">
  <cues>
    <library name="DescribeAmount">
      <params>
        <param name="Amount" />
        <param name="Offset" default="1" />
      </params>
      <actions>
        <set_value name="$Result" exact="$Amount + $Offset" />
        <debug_text text="$Result" />
      </actions>
    </library>
    <cue name="Small" ref="DescribeAmount">
      <param name="Amount" value="4" />
    </cue>
    <cue name="Large" ref="DescribeAmount">
      <param name="Amount" value="10" />
      <param name="Offset" value="2" />
    </cue>
  </cues>
</mdscript>
```



## What happens


With fresh script state, Small calculates 5 and Large calculates 12. `debug_text` sends these values to the diagnostic log with [script output enabled](wiki:debugging). Their message order is unspecified. This example has not been executed in game.



Exercise: change only Small's Amount. Its expected result should change without editing the template or Large's inputs.



## Scope


Parameters become `$Amount` and `$Offset` when the cue is enabled. Use qualified `ref="md.ScriptName.LibraryName"` for another script. Behavior attributes on a referencing cue do not override the template: except for its name, behavior comes from the library.



Updating an enabled cue requires [save/load checks](wiki:md-persistence). Egosoft's shared guide describes XR/X4 MD structure; verify the actual action set against X4. Continue with [cues](wiki:md-cues) and [variables](wiki:md-variables).