One of the greatest (mostly) unknown abilities of robots.txt is wildcard pattern matching. We know how robots.txt can block files and directories from being crawled, but in the case of URLs with unique paramaters and duplicate content issues, did you know that Google and Yahoo respect wildcards (this was verified by connections at the engines – but MSN said they do not respect pattern matching “at this time”).
If you have URLs with unique parameters – for example, UTM with Google analytics, paid search tags, and so on – you can create a robots.txt entry like this:
User-agent: *
Disallow: /*utm
How cool is that? Remember, this only should be employed if you have very unique parameters. If your parameters are keyworded, and that keyword appears as other directories or page names, they will get blocked too… quite possibly to your dismay.
More from Google’s Webmaster Blog.
Bill Sebald - Ex-big agency guy, now focused on helping small and medium sized business. I've been practicing SEO since 1998. I started the SEO practice at a major digital agency owned by eBay and helped develop SEO products for one of the largest ecommerce platforms. I'm a proud member of the Philadelphia SEO scene. I'm passionate about search, writing, UX, CRO, and psychology in marketing.
seojedi
Bill, you just saved me tons of hours coding conditional redirects!
seojedi
Bill, you just saved me tons of hours coding conditional redirects!
Premal
What is matt cutts’ email address? I assume he’s your contact, eh?
Premal
What is matt cutts’ email address? I assume he’s your contact, eh?
Bill
No. Wrong sex. My contact is not Matt Cutts. But I did discover this on the Google Blog to help add validity.
Bill
No. Wrong sex. My contact is not Matt Cutts. But I did discover this on the Google Blog to help add validity.