Web spiders and crawlers search the Internet for new and updated web pages true or False

Overview of Google crawlers (user agents)

"Crawler" (sometimes also called a "robot" or "spider") is a generic term for any program that is used to automatically discover and scan websites by following links from one webpage to another. Google's main crawler is called Googlebot. This table lists information about the common Google crawlers you may see in your referrer logs, and how to specify them in robots.txt, the robots meta tags, and the X-Robots-Tag HTTP directives.

The following table shows the crawlers used by various products and services at Google:

• The user agent token is used in the User-agent: line in robots.txt to match a crawler type when writing crawl rules for your site. Some crawlers have more than one token, as shown in the table; you need to match only one crawler token for a rule to apply. This list is not complete, but covers most of the crawlers you might see on your website.
• The full user agent string is a full description of the crawler, and appears in the HTTP request and your web logs.

A note about Chrome/W.X.Y.Z in user agents

Wherever you see the string Chrome/W.X.Y.Z in the user agent strings in the table, W.X.Y.Z is actually a placeholder that represents the version of the Chrome browser used by that user agent: for example, 41.0.2272.96. This version number will increase over time to match the latest Chromium release version used by Googlebot.

If you are searching your logs or filtering your server for a user agent with this pattern, use wildcards for the version number rather than specifying an exact version number.

User agents in robots.txt

Where several user agents are recognized in the robots.txt file, Google will follow the most specific. If you want all of Google to be able to crawl your pages, you don't need a robots.txt file at all. If you want to block or allow all of Google's crawlers from accessing some of your content, you can do this by specifying Googlebot as the user agent. For example, if you want all your pages to appear in Google Search, and if you want AdSense ads to appear on your pages, you don't need a robots.txt file. Similarly, if you want to block some pages from Google altogether, blocking the Googlebot user agent will also block all Google's other user agents.

But if you want more fine-grained control, you can get more specific. For example, you might want all your pages to appear in Google Search, but you don't want images in your personal directory to be crawled. In this case, use robots.txt to disallow the Googlebot-Image user agent from crawling the files in your personal directory (while allowing Googlebot to crawl all files), like this:

User-agent: Googlebot
Disallow:

User-agent: Googlebot-Image
Disallow: /personal

To take another example, say that you want ads on all your pages, but you don't want those pages to appear in Google Search. Here, you'd block Googlebot, but allow the Mediapartners-Google user agent, like this:

User-agent: Googlebot
Disallow: /

User-agent: Mediapartners-Google
Disallow:

Some pages use multiple robots meta tags to specify directives for different crawlers, like this:

<meta name="robots" content="nofollow">
<meta name="googlebot" content="noindex">

In this case, Google will use the sum of the negative directives, and Googlebot will follow both the noindex and nofollow directives. More detailed information about controlling how Google crawls and indexes your site.

Controlling crawl speed

Each Google crawler accesses sites for a specific purpose and at different rates. Google uses algorithms to determine the optimal crawl rate for each site. If a Google crawler is crawling your site too often, you can reduce the crawl rate.

Retired Google crawlers

The following Google crawlers are no longer in use, and are only noted here for historical reference.