Google is adding a new feature in Webmaster Tools that will leave no doubt when a site’s search rankings are affected by a manual webspam action.

It’s called the Manual Actions viewer, and it’s available today under the “Search Traffic” tab. The new tool complements the email notifications that Google already sends when it takes manual action against a website, giving site owners a way to check their site’s status on their own at any time.

Google says fewer than two percent of domains in its index are manually removed due to spam, so the vast majority of webmasters won’t find anything when they visit the Manual Actions viewer other than a message saying “No manual webspam actions found.”

But for sites that are affected, the Manual Actions viewer will show existing webspam problems under two headings: Site-wide matches and Partial matches. In both cases, Google will indicate what type of problem exists from a list of about a dozen categories — things like “hidden text and/or keyword stuffing,” “thin content,” “pure spam” and others.

When there are Partial matches listed, Google will also show the affected URLs for each type of spam problem. There’s a limit, though, of 1,000 URLs per type of problem listed. Google says this will be more than enough for all but the largest sites (like YouTube, for example). In the screenshots below, you can see that a sample site has a “Partial match” notice about thin content, and Google is showing a half-dozen affected URLs.

As you can see above, there’s also quick access to a new “Request a Review” button. This will be available any time there are manual webspam actions listed. Clicking that opens a pop-up window where the webmaster can give Google details on how its problems have been fixed.

Simultaneously, visitors to Google’s existing page about reconsideration requests will first be invited to use the Manual Actions viewer to make sure that there’s really a manual action in place.

This new tool is part of Google’s ongoing efforts to increase communication with webmasters about spam and other issues affecting their sites. Each of the dozen or so categories of manual actions used in this new tool is also getting a dedicated help/info page (available from the “Learn More” link in the screenshot above) with some new videos from Matt Cutts explaining the type of webspam problem that Google has identified.

The Manual Actions viewer is available now in all languages that Google Webmaster Tools currently supports.