 <blockquote> <p>Professional Excel Development by Stephen Bullen describes how to register UDFs, which allows a description to appear in the Function Arguments dialog:</p> </blockquote> <pre><code>Function IFERROR(ByRef ToEvaluate As Variant, ByRef Default As Variant) As Variant If IsError(ToEvaluate) Then IFERROR = Default Else IFERROR = ToEvaluate End If End Function Sub RegisterUDF() Dim s As String s = "Provides a shortcut replacement for the common worksheet construct" &amp; vbLf _ &amp; "IF(ISERROR(&lt;expression&gt;, &lt;default&gt;, &lt;expression&gt;)" Application.MacroOptions macro:="IFERROR", Description:=s, Category:=9 End Sub Sub UnregisterUDF() Application.MacroOptions Macro:="IFERROR", Description:=Empty, Category:=Empty End Sub </code></pre> <p>From: <a href="http://www.ozgrid.com/forum/showthread.php?t=78123&amp;page=1" rel="nofollow noreferrer">http://www.ozgrid.com/forum/showthread.php?t=78123&amp;page=1</a></p> <p>To show the Function Arguments dialog, type the function name and press <kbd>Ctrl</kbd><kbd>A</kbd>. Alternatively, click the "fx" symbol in the formula bar:</p> <p><img src="https://i.stack.imgur.com/7CMpJ.png" alt="enter image description here"></p>