To set up the target in the configuration file, use the following syntax:

<nlog xmlns="http://www.nlog-project.org/schemas/NLog.xsd" 
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"> 
  <targets> 
    <target name="msgbox" xsi:type="MessageBox" layout="${longdate}: ${message}" 
            caption="${level}"/> 
  </targets> 
  <rules> 
    <logger name="*" minlevel="Debug" writeTo="msgbox"/> 
  </rules> 
</nlog> 

This assumes just one target and a single rule. More configuration options are described here.

The result is a message box:

To set up the log target programmatically use code like this:

using System; 
 
using NLog; 
using NLog.Targets; 
 
class Example 
{ 
    static void Main(string[] args) 
    { 
        MessageBoxTarget target = new MessageBoxTarget(); 
        target.Layout = "${longdate}: ${message}"; 
        target.Caption = "${level} message"; 
 
        NLog.Config.SimpleConfigurator.ConfigureForTargetLogging(target, LogLevel.Debug); 
 
        Logger logger = LogManager.GetLogger("Example"); 
        logger.Debug("log message"); 
    } 
}