Preview - Sidekicks

Looking for a “Preview” enhanced through “sidekicks” that allow a user using preview to:
[li]Validate HTML/CSS for page[/li][li]Validate SEO for page[/li][li]Emulate page on mobile device (viewport resizing)[/li][li]Switch template for preview[/li][li]Enable developers to add additional “sidekicks”[/li][/ul]

I’m sure you could modify:

We modified it so that it is completely javascript based (i mean you don’t need greasemonkey) and checks the url and a cookie to display a “debug” bar of sorts…