---
title: Mission Director cues and events
summary: MD script structure, repeatable handlers and reasons a cue may not fire.
section: scripting
kind: guide
status: example
updated: 2026-10-27
tags: ["X4","modding","md","cues"]
sources: ["https://wiki.egosoft.com/X%20Rebirth%20Wiki/Modding%20support/Mission%20Director%20Guide/"]
---
## Script structure


MD handlers live under `mdscript → cues → cue`, with effects in `actions`. A cue without conditions can perform brief initialization. The standalone template below initializes a cue-owned variable; see [variable scope](wiki:md-variables).




```xml
<mdscript name="WikiExample">
  <cues>
    <cue name="Init">
      <actions>
        <set_value name="$Count" exact="0" />
      </actions>
    </cue>
  </cues>
</mdscript>
```

## Event handler


Insert the UI event handler below inside `cues`. `instantiate=true` permits repeated events to use separate instances. Do not put unrelated requests' mutable state in a shared variable without an explicit reason.




```xml
<cue name="Read" instantiate="true" namespace="this">
  <conditions>
    <event_ui_triggered screen="'WikiExample'" control="'read'" />
  </conditions>
  <actions>
    <set_value name="$Payload" exact="event.param3" />
    <debug_text text="'Wiki read request received'" />
  </actions>
</cue>
```

## A condition without an event


A bare `check_value` condition needs an appropriate checking mode, such as `checkinterval` or `onfail`, according to the cue contract. XSD validity does not establish successful import or execution. Use conditional blocks to limit actions; do not transplant library mechanisms into regular cues without checking their contracts. The [library/ref example](wiki:md-libraries) explains template reuse.



## Debugging


Distinguish file loading, event reception and the actual effect. A log line answers only the question it was designed to observe. See [Lua ↔ MD](wiki:md-lua-bridge) and [game testing](wiki:testing).