Windows light XML validator, works with non ".xml" files

Question

I often use Firefox to quickly spot what is the problem in a malformed XML file.
Unfortunately it only works if the filename extension is .xml.

What tool could I use instead?

Requirements:

• Very light and fast
• Minimalist GUI, command line acceptable too if fast to use
• Shows where XML is malformed (just XML is enough, but bonus for XML Schema)
• Open source
• Usable offline

Answer 1

Notepad++ Obviously :)

It's by default really light since it's a pure editor.
But for XML support you will need a plugin like
XML TOOLS and an installation guide

A screenshot of the plugin menu:

The only "trap" with your requirements is that when checking XML syntax a window pops-up showing where the first problem occured like this:

But I really can not remember a program which shows (like highlighted in red) where the xml is malformed generally.

Forgot to mention that the second image is when trying to validate a non-XML file, the plugin works generally with files opened with any extension

Answer 2

You can use XML Explorer:

• free and open source
• Windows
• fast and lightweight
• validates XML documents using XSD Schema (specified in the document), shows a list of validation errors, and double-clicking an error navigates and selects the node.