User-agent: *
Disallow: /
These two parts of the text are essential. The first part, User-agent:, tells a crawler what user
agent, or crawler, you’re commanding. The asterisk (*) indicates that all crawlers are covered, but
you can specify a single crawler or even multiple crawlers.
The second part, Disallow:, tells the crawler what it is not allowed to access. The slash (/) indicates
“all directories.” So in the preceding code example, the robots.txt file is essentially saying that
“all crawlers are to ignore all directories.”
When you’re writing robots.txt, remember to include the colon (:) after the User-agent indicator
and after the Disallow indicator. The colon indicates that important information follows to which
the crawler should pay attention.
You won’t usually want to tell all crawlers to ignore all directories. Instead, you can tell all crawlers
to ignore your temporary directories by writing the text like this:
User-agent: *
Disallow: /tmp/
Or you can take it one step further and tell all crawlers to ignore multiple directories:
User-agent: *
Disallow: /tmp/
Disallow: /private/
Disallow: /links/listing.html
That piece of text tells the crawler to ignore temporary directories, private directories, and the web
page (title Listing) that contains links — the crawler won’t be able to follow those links.
One thing to keep in mind about crawlers is that they read the robots.txt file from top to bottom
and as soon as they find a guideline that applies to them, they stop reading and begin crawling your
site. So if you’re commanding multiple crawlers with your robots.txt file, you want to be careful how
you write it.
This is the wrong way:
User-agent: *
Disallow: /tmp/
User-agent: CrawlerName
Disallow: /tmp/
Disallow: /links/listing.html
This bit of text tells crawlers first that all crawlers should ignore the temporary directories. So
every crawler reading that file will automatically ignore the temporary files. But you’ve also told a
specific crawler (indicated by CrawlerName) to disallow both temporary directories and the links
on the Listing page. The problem is, the specified crawler will never get that message because it
has already read that all crawlers should ignore the temporary directories.
If you want to command multiple crawlers, you need to first begin by naming the crawlers you want
to control. Only after they’ve been named should you leave your instructions for all crawlers. Written
properly, the text from the preceding code should look like this:
User-agent: CrawlerName
Disallow: /tmp/
Disallow: /links/listing.html
User-agent: *
Disallow: /tmp/
Each search engine crawler goes by a different name, and if you look at your web server log, you’ll
probably see that name. Here’s a quick list of some of the crawler names that you’re likely to see in
that web server log:
Google: Googlebot
MSN: MSNbot
Yahoo! Web Search: Yahoo SLURP or just SLURP
Ask: Teoma
AltaVista: Scooter
LookSmart: MantraAgent
WebCrawler: WebCrawler
SearchHippo: Fluffy the Spider
These are just a few of the search engine crawlers that might crawl across your site. You can find a
complete list along with the text of the Robots Exclusion Standard document on the Web Robots
Pages (www.robotstxt.org). Take the time to read the Robots Exclusion Standard document.
It’s not terribly long, and reading it will help you understand how search crawlers interact with
your web site. That understanding can also help you learn how to control crawlers better when
they come to visit.
It pays to know which crawler belongs to what search engine, because there are some spambots and
other malicious crawlers out there that are interested in crawling your site for less than ethical reasons.
If you know the names of these crawlers, you can keep them off of your site and keep your
users’ information safe. Spambots in particular are troublesome, because they crawl along the Web
searching out and collecting anything that appears to be an e-mail address. These addresses are then
collected and sold to marketers or even people who are not interested in legitimate business opportunities.
Most spambots will ignore your robots.txt file.
You can view the robots.txt file for any web site that has one by adding the robots
.txt extension to the base URL of the site. For example, www.sampleaddress.com/
robots.txt will display a page that shows you the text file guiding robots for that site. If you use
that extension on a URL and it doesn’t pull up the robots.txt file, then the web site does not have one.
If you don’t have a robots.txt file, you can create one in any text editor. And keep in mind that not
everyone wants or needs to use the robots.txt file. If you don’t care who is crawling your site, then
don’t even create the file. Whatever you do, though, don’t use a blank robots.txt file. Crawlers automatically
assume an empty file means you don’t want your site to be crawled. So using the blank file
is a good way to keep yourself out of search engine results.
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