I was working on a spreadsheet that submitted XML data to a web service and the XML that was being generated by the XmlDocument object was not very tidy. Normally with C# I use Tidy.NET to clean up the HTML or XML, but since this was being used in Excel I didn't want to have any external dependencies. I found the following code online and it seems to work pretty well:

Option Explicit

' http://www.vb-helper.com/howto_formatted_xml_document.html
' Add formatting to the document.
Public Sub FormatXmlDocument(ByVal xml_doc As DOMDocument)
    FormatXmlNode xml_doc.documentElement, 0
End Sub

' Add formatting to this element. Indent it and add a
' carriage return before its children. Then recursively
' format the children with increased indentation.
Private Sub FormatXmlNode(ByVal node As IXMLDOMNode, _
                          ByVal indent As Integer)
Dim child As IXMLDOMNode
Dim text_only As Boolean

    ' Do nothing if this is a text node.
    If TypeOf node Is IXMLDOMText Then Exit Sub

    ' See if this node contains only text.
    text_only = True
    If node.hasChildNodes Then
        For Each child In node.childNodes
            If Not (TypeOf child Is IXMLDOMText) Then
                text_only = False
                Exit For
            End If
        Next child
    End If

    ' Process child nodes.
    If node.hasChildNodes Then
        ' Add a carriage return before the children.
        If Not text_only Then
            node.insertBefore _
                node.ownerDocument.createTextNode(vbCrLf), _
                node.FirstChild
        End If

        ' Format the children.
        For Each child In node.childNodes
            FormatXmlNode child, indent + 2
        Next child
    End If

    ' Format this element.
    If indent > 0 Then
        ' Indent before this element.
        node.parentNode.insertBefore _
            node.ownerDocument.createTextNode(Space$(indent)), _
            node

        ' Indent after the last child node.
        If Not text_only Then _
            node.appendChild _
                node.ownerDocument.createTextNode(Space$(indent))

        ' Add a carriage return after this node.
        If node.nextSibling Is Nothing Then
            node.parentNode.appendChild _
                node.ownerDocument.createTextNode(vbCrLf)
        Else
            node.parentNode.insertBefore _
                node.ownerDocument.createTextNode(vbCrLf), _
                node.nextSibling
        End If
    End If
End Sub