User agent

A user agent is the client application used with a particular network protocol; the phrase is most commonly used in reference to those which access the World Wide Web. Web user agents range from web browsers to search engine crawlers ("spiders"), as well as screen readers and braille browsers used by people with disabilities.

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When Internet users visit a web site, a text string is generally sent to identify the user agent to the server. This forms part of the HTTP request, prefixed with User-agent: or User-Agent: and typically includes information such as the application name, version, host operating system, and language. Bots, such as web crawlers, often also include a URL and/or e-mail address so that the webmaster can contact the operator of the bot.

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The user-agent string is one of the criteria by which crawlers can be excluded from certain pages or parts of a website using the "Robots Exclusion Standard" (robots.txt). This allows webmasters who feel that certain parts of their website should not be included in the data gathered by a particular crawler, or that a particular crawler is using up too much bandwidth, to request that crawler not to visit those pages.

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Client: The term client may have the following meanings....

Network protocol: REDIRECT Protocol (computing)...

World Wide Web: :For the world's first web browser, see WorldWideWeb....

User agent related Images and Photos (experimental)

user error	Triple Agent	Secret Agent	Special Agent
Confidential Agent (DVD)	Secret Agent Phone Holder	Enemy Agent 1940	Agent of S.H.I.E.L.D. Marvel Tee for Men
Agent Cody Banks 2- Destination London	NCIS Federal Agent Hoodie	NCIS Special Agent Jacket	NCIS Special Agent Jacket