The robot exclusion standard, also known as the Robots Exclusion Protocol or robots.txt protocol, is a convention to prevent cooperating web spiders and other web robots from accessing all or part of a website which is otherwise publicly viewable. Robots are often used by search engines to categorize and archive web sites, or by webmasters to proofread source code. The standard complements Sitemaps, a robot inclusion standard for websites.
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About the standard
A robots.txt file on a website will function as a request that specified robots ignore specified files or directories in their search. This might be, for example, out of a preference for privacy from search engine results, or the belief that the content of the selected directories might be misleading or irrelevant to the categorization of the site as a whole, or out of a desire that an application only operate on certain data.
For websites with multiple subdomains, each subdomain must have its own robots.txt file. If example.com had a robots.txt file but a.example.com did not, the rules that would apply for example.com would not apply to a.example.com.
Disadvantages
The protocol is purely advisory. It relies on the cooperation of the web robot, so that marking an area of a site out of bounds with robots.txt does not guarantee privacy. Some web site administrators have tried to use the robots file to make private parts of a website invisible to the rest of the world, but the file is necessarily publicly available and its content is easily checked by anyone with a web browser.
There is no official standards body or RFC for the robots.txt protocol. It was created by consensus in June 1994 by members of the robots mailing list (robots-request@nexor.co.uk). The information specifying the parts that should not be accessed is specified in a file called robots.txt in the top-level directory of the website. The robots.txt patterns are matched by simple substring comparisons, so care should be taken to make sure that patterns matching directories have the final '/' character appended, otherwise all files with names starting with that substring will match, rather than just those in the directory intended.
Automated Content Access Protocol
Main article: Automated Content Access ProtocolACAP, which is a possible plug-in for the Robots Exclusion Standard, was released as v1.0 on November 30, 2007.
Examples
This example allows all robots to visit all files because the wildcard "*" specifies all robots:
User-agent: * Disallow:
This example keeps all robots out:
User-agent: * Disallow: /
The next is an example that tells all crawlers not to enter four directories of a website:
User-agent: * Disallow: /cgi-bin/ Disallow: /images/ Disallow: /tmp/ Disallow: /private/
Example that tells a specific crawler not to enter one specific directory:
User-agent: BadBot # replace the 'BadBot' with the actual user-agent of the bot Disallow: /private/
Example that tells all crawlers not to enter one specific file:
User-agent: * Disallow: /directory/file.html
Note that all other files in the specified directory will be processed.
Example demonstrating how comments can be used:
# Comments appear after the "#" symbol at the start of a line, or after a directive User-agent: * # match all bots Disallow: / # keep them out
Compatibility
In order to prevent access to all pages by robots, do not use
Disallow: * # DO NOT USE! Use "/" instead.
as this is not a stable standard extension.
Instead:
Disallow: /
should be used.
Nonstandard extensions
Crawl-delay directive
Several major crawlers support a Crawl-delay parameter, set to the number of seconds to wait between successive requests to the same server: [1] [2]
User-agent: * Crawl-delay: 10
Allow directive
Some major crawlers support an Allow directive which can counteract a following Disallow directive.[3] [4] This is useful when you disallow an entire directory but still want some HTML documents in that directory crawled and indexed. While by standard implementation the first matching robots.txt pattern always wins, Google's implementation differs in that it first evaluates all Allow patterns and only then all Disallow patterns. Yet, in order to be compatible to all robots, if you want to allow single files inside an otherwise disallowed directory, you need to place the Allow directive(s) first, followed by the Disallow, for example:
Allow: /folder1/myfile.html Disallow: /folder1/
This example will Disallow anything in /folder1/ except /folder1/myfile.html, since the latter will match first. In case of Google, though, the order is not important.
Sitemap
Some crawlers support a Sitemap directive, allowing multiple sitemaps in the same robots.txt in the form:[5]
Sitemap: http://www.gstatic.com/s2/sitemaps/profiles-sitemap.xml Sitemap: http://www.google.com/hostednews/sitemap_index.xml
Extended standard
An Extended Standard for Robot Exclusion has been proposed, which adds several new directives, such as Visit-time and Request-rate. For example:
User-agent: * Disallow: /downloads/ Request-rate: 1/5 # maximum rate is one page every 5 seconds Visit-time: 0600-0845 # only visit between 06:00 and 08:45 UTC (GMT)
The first version of the Robot Exclusion standard does not mention anything about the "*" character in the Disallow: statement. Some crawlers like Googlebot and Slurp recognize strings containing "*", while MSNbot and Teoma interpret it in different ways. [6]
References
- ^ "How can I reduce the number of requests you make on my web site?" (HTML). Yahoo! Slurp. http://help.yahoo.com/l/us/yahoo/search/webcrawler/slurp-03.html. Retrieved on 2007-03-31.
- ^ "MSNBot is crawling a site too frequently" (HTML). Troubleshoot issues with MSNBot and site crawling. http://search.msn.com/docs/siteowner.aspx?t=SEARCH_WEBMASTER_FAQ_MSNBotIndexing.htm&FORM=WFDD#D. Retrieved on 2007-02-08.
- ^ "Webmaster Help Center - How do I block Googlebot?" (HTML). http://www.google.com/support/webmasters/bin/answer.py?answer=40364. Retrieved on 2007-11-20.
- ^ "How do I prevent my site or certain subdirectories from being crawled? - Yahoo Search Help" (HTML). http://help.yahoo.com/l/us/yahoo/search/webcrawler/slurp-02.html. Retrieved on 2007-11-20.
- ^ "Yahoo! Search Blog - Webmasters can now auto-discover with sitemaps" (HTML). http://ysearchblog.com/2007/04/11/webmasters-can-now-auto-discover-with-sitemaps/. Retrieved on 2009-03-23.
- ^ "Search engines and dynamic content issues" (HTML). MSNbot issues with robots.txt. http://www.serbanghita.com/search-engines-dynamic-content-issues.html. Retrieved on 2007-04-01.
See also
- BotSeer - search engine for robots.txt files
- Distributed web crawling
- Focused crawler
- Internet Archive
- Library of Congress Digital Library project
- National Digital Information Infrastructure and Preservation Program
- Nofollow and Spam in blogs
- Spider trap
- Web archiving
- Web crawler
- Meta Elements for Search Engines
External links
- Robots Exclusion
- Using the robots.txt analysis tool
- About Robots.txt at the Mediawiki website
- List of Bad Bots - rogue robots and spiders which ignore these guidelines
- More info about Robots.txt
- Wikipedia's Robots.txt - an example
- Robots.txt Generator + Tutorial
- Robots.txt Generator Tool
- Robots.txt is not a security measure
- History of robots.txt -(how Charles Stross prompted its invention; original comment on Slashdot)
- BotSeer, Robots.txt search engine
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Categories: World Wide Web
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Search Newz
This would see links to their content removed from Google and all other major search engines that follow the Robots.txt protocol. ...
ilovekhym
Sun, 12 Jul 2009 20:53:00 GM
The Gatekeeper: . robots.txt. . Posted by ilovekhym | 1:53 PM | Recommended Blogging Tips | 0 comments . The Robots Exclusion Protocol from 1994 defines "a method that allows Web site administrators to indicate to visiting robots which ...
Q. I've just logged into my blog using Flock and a download prompt would automatically let me select whether I want to download a certain robots.txt ASCII file. What is it and why is it making me download? (I didn't, by instinct.) Safari doesn't show this prompt and I can't access the site using Opera! And though Flock is based from Firefox, FF doesn't show it either. Is it just coincidental or just Flock's problem?
Asked by kevz - Tue Apr 1 00:55:05 2008 - - 2 Answers - 0 Comments
