zlacker

Right click -> View source -> Ctrl+A (select all) -> Ctrl+C (Copy to clipboard) -> Open your preferred text editor (mine is Notepad++) -> Ctrl+V (Paste from clipboard) -> Replace ">" with ">\r" -> enjoy the source reading.

Takes max 10 seconds, on any site. Can you do it in less than 10 seconds using that validator?

>>unnoui+(OP)
That would give you new lines, but not indentation..

But my point was that the markup is invalid.