The WMT 'Crawl Errors' report has a new feature today.
As you mouseover the list of URLs with errors under the graph, there's a pop-up pane for each one.
I only have 404 and 410 errors on this site. The pop-up pane contains a direct link to the listed URL and a box with "preview not available" written in it for each one. The preview doesn't show what the error page looks like.
You can still click through to the bigger box that lists the first found date and the last crawled date and lists the pages that link to this URL.
Mouseover of each URL makes an immediate call to the site from IP
with same or different IPs for each request, using user agent:
Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/536.8 (KHTML, like Gecko; Google Web Preview) Chrome/19.0.1084.36 Safari/536.8
The referrer is
I can't see much point in having previews for stuff that doesn't exist, other than to show that for temporary errors the page is now working again.
Presumably, people will find the previews useful for some of the other types of errors they may have on their sites?