What Does Your User Agent Say About You?


A user agent is a computer program representing a person, for example, a browser in a Web context.

Besides a browser, a user agent could be a bot scraping webpages, a download manager, or another app accessing the Web. Along with each request they make to the server, browsers include a self-identifying User-Agent HTTP header called a user agent (UA) string. This string often identifies the browser, its version number, and its host operating system.

Spam bots, download managers, and some browsers often send a fake UA string to announce themselves as a different client. This is known as user agent spoofing.

The user agent string can be accessed with JavaScript on the client side using the navigator.userAgent property.

A typical user agent string looks like this: "Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:35.0) Gecko/20100101 Firefox/35.0".


User Agent String

Browser Data

Robots User Agent

Christina Perez
• Tuesday, 05 July, 2022
• 23 min read

Mozilla/5.0 (Linux; Android 4.2.1; en-us; Nexus 5 Build/JOP40D) Apple WebKit/535.19 (HTML, like Gecko; googleweblight) Chrome/38.0.1025.166 Mobile Safari/535.19 ‡ Chrome/ W.×.Y.Z in user agents Where several user -agents are recognized in the robots .txt file, Google will follow the most specific.

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Some pages use multiple robots meta tags to specify directives for different crawlers, like this: Search engines robots are programs that visit your site and follow the links on it to learn about your pages.

Bots generally check the robots .txt file before visiting your site. The best way to edit it is to log in to your web host via a free FTP client like FileZilla, then edit the file with a text editor like Notepad (Windows) or TextEd it (Mac).

If you don’t know how to login to your server via FTP, contact your web hosting company to ask for instructions. Some plugins, like Yoast SEO, also allow you to edit the robots .txt file from within your WordPress dashboard.

In effect, this will tell all robots and web crawlers that they are not allowed to access or crawl your site. Important: Disallowing all robots on a live website can lead to your site being removed from search engines and can result in a loss of traffic and revenue.

You exclude the files and folders that you don’t want to be accessed, everything else is considered to be allowed. You simply put a separate line for each file or folder that you want to disallow.

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The reason for this setting is that Google Search Console used to report an error if it wasn’t able to crawl the admin-ajax.php file. This sitemap should contain a list of all the pages on your site, so it makes it easier for the web crawlers to find them all.

If you want to block your entire site or specific pages from being shown in search engines like Google, then robots .txt is not the best way to do it. Search engines can still index files that are blocked by robots, they just won’t show some useful metadata.

On WordPress, if you go to Settings Reading and check “Discourage search engines from indexing this site” then a no index tag will be added to all your pages. In some cases, you may want to block your entire site from being accessed, both by bots and people.

Also, if you are trying to hide a folder from your website, then just putting it in the robots .txt file may not be a smart approach. Just try adding / robots .txt to the home page URL of your favorite websites.

If you want to make sure that your robots .txt file is working, you can use Google Search Console to test it. Using it can be useful to block certain areas of your website, or to prevent certain bots from crawling your site.

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If you are going to edit your robots .txt file, then be careful because a small mistake can have disastrous consequences. For example, if you misplace a single forward slash then it can block all robots and literally remove all of your search traffic until it gets fixed.

The REP also includes directives like meta robots, as well as page-, subdirectory-, or site-wide instructions for how search engines should treat links (such as “follow” or “no follow”). In practice, robots .txt files indicate whether certain user agents (web-crawling software) can or cannot crawl parts of a website.

Using this syntax in a robots .txt file would tell all web crawlers not to crawl any pages on, including the homepage. Using this syntax in a robots .txt file tells web crawlers to crawl all pages on, including the homepage.

After arriving at a website but before spidering it, the search crawler will look for a robots .txt file. In order to be found, a robots .txt file must be placed in a website’s top-level directory.

This is especially common with more nefarious crawlers like malware robots or email address scrapers. It’s generally a best practice to indicate the location of any sitemaps associated with this domain at the bottom of the robots .txt file.

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But, they’ll only look for that file in one specific place: the main directory (typically your root domain or homepage). In order to ensure your robots .txt file is found, always include it in your main directory or root domain.

If you found you didn’t have a robots .txt file or want to alter yours, creating one is a simple process. If you have pages to which you want equity to be passed, use a different blocking mechanism other than robots .txt.

Do not use robots .txt to prevent sensitive data (like private user information) from appearing in SERP results. If you want to block your page from search results, use a different method like password protection or the no index meta directive.

Most user agents from the same search engine follow the same rules so there’s no need to specify directives for each of a search engine’s multiple crawlers, but having the ability to do so does allow you to fine-tune how your site content is crawled. If you change the file and want to update it more quickly than is occurring, you can submit your robots .txt URL to Google.

Robots .txt dictates site or directory-wide crawl behavior, whereas meta and x- robots can dictate indexation behavior at the individual page (or page element) level. MOZ Pro can identify whether your robots .txt file is blocking our access to your website.


A robots .txt file lives at the root of your site. Each rule blocks (or allows) access for a given crawler to a specified file path in that website.

The user agent named “Google bot” crawler should not crawl the folder or any subdirectories. Don't use a word processor; word processors often save files in a proprietary format and can add unexpected characters, such as curly quotes, which can cause problems for crawlers.

This tool enables you to test the syntax and behavior against your site. The robots .txt file must be located at the root of the website host to which it applies.

If you're unsure about how to access your website root, or need permissions to do so, contact your web hosting service provider. If you can't access your website root, use an alternative blocking method such as meta tags.

Robots .txt must be a UTF-8 encoded text file (which includes ASCII). Groups are processed from top to bottom, and a user agent can match only one rule set, which is the first, most-specific rule that matches a given user agent.

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Supports the * wildcard for a path prefix, suffix, or entire string. Allow: A directory or page, relative to the root domain, that should be crawled by the user agent just mentioned.

Supports the * wildcard for a path prefix, suffix, or entire string. Please read the full documentation, as the robots .txt syntax has a few tricky parts that are important to learn.

Keep in mind that in some situations URLs from the website may still be indexed, even if they haven't been crawled. Note: this does not match the various Abbot crawlers, which must be named explicitly.

Remember that you shouldn't use robots .txt to block access to private content: use proper authentication instead. URLs disallowed by the robots .txt file might still be indexed without being crawled, and the robots .txt file can be viewed by anyone, potentially disclosing the location of your private content.

Disallow crawling of a single webpage by listing the page after the slash: This implementation hides your pages from search results, but the Mediapartners-Google web crawler can still analyze them to decide what ads to show visitors to your site.

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For instance, the sample code blocks any URLs that end with .xls : His main expertise is open source software development and digital marketing.

The robots .txt file is one of the main ways of telling a search engine where it can and can’t go on your website. All major search engines support the basic functionality it offers, but some of them respond to some extra rules which can be useful too.

So they created the humans.txt standard as a way of letting people know who worked on a website, amongst other things. Before a search engine spiders any page on a domain it hasn’t encountered before, it will open that domain’s robots .txt file, which tells the search engine which URLs on that site it’s allowed to index.

Search engines typically cache the contents of the robots .txt, but will usually refresh it several times a day, so changes will be reflected fairly quickly. Blocking all query parameters from being crawled will help make sure the search engine only spiders your site’s main URLs and won’t go into the enormous trap that you’d otherwise create.

If you want to reliably block a page from showing up in the search results, you need to use a meta robots no index tag. That means that, in order to find the no index tag, the search engine has to be able to access that page, so don’t block it with robots .txt.

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With only one character less, the example below would allow all search engines to crawl your entire site. It would not block Google from crawling the /photo directory, as these lines are case-sensitive.

“Officially”, the robots .txt standard doesn’t support regular expressions or wildcards, however, all major search engines do understand it. These directives are not supported by all search engine crawlers so make sure you’re aware of their limitations.

The only other way of achieving the same result without an allow directive would have been to specifically disallow every single file in the admin folder. But because only Yandex supports the host directive, we wouldn’t advise you to rely on it, especially as it doesn’t allow you to define a scheme (HTTP or HTTPS) either.

A better solution that works for all search engines would be to 301 redirect the hostnames that you don’t want in the index to the version that you do want. And while these search engines have slightly different ways of reading the directive, the end result is basically the same.

By setting a crawl delay of 10 seconds you’re only allowing these search engines to access 8,640 pages a day. On the other hand, if you get next to no traffic from these search engines, it’s a good way to save some bandwidth.

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You can, of course, also submit your XML sitemaps to each search engine using their respective webmaster tools solutions, and we strongly recommend you do, because search engine webmaster tools programs will give you lots of valuable information about your site. If you don’t want to do that, adding a sitemap line to your robots .txt is a good quick alternative.

You wouldn’t be the first to accidentally use robots .txt to block your entire site, and to slip into search engine oblivion! In July 2019, Google announced that they were making their robots .txt Parser open source.

That means that, if you really want to get into the nuts and bolts, you can go and see how their code works (and, even use it yourself, or propose modifications to it). Robots .txt is a file which should be stored in the root directory of every website.

The main purpose if this file is to restrict some or all content on your website by search engines. Simply tell Search Robots which page you would like them not to visit.

You only need this file when you want your website content should not index by search engine. It must be the main directory otherwise user agents/ search engines will not be able to find it.

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Lets a robot or search engine wants to visit a website URL example: HTTP(s):// If search engines found robots .txt file, then it checks the content is allowed for indexing or not.

Disallow crawling of a single webpage by listing the page after the slash: In this article we will deal only how to create and use robots .txt in core.

If / robots .txt file not found it shows default text In this scenario if the URL matches to / robots .txt it ends the request.

During the first browser war, many web servers were configured to send web pages that required advanced features, including frames, to clients that were identified as some version of Mozilla only. Other browsers were considered to be older products such as Mosaic, Cello, or Samba, and would be sent a bare-bones HTML document.

Automated agents are expected to follow rules in a special file called robots .txt “. The popularity of various Web browser products has varied throughout the Web's history, and this has influenced the design of websites in such a way that websites are sometimes designed to work well only with particular browsers, rather than according to uniform standards by the World Wide Web Consortium (W3C) or the Internet Engineering Task Force (IETF).

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Websites often include code to detect browser version to adjust the page design sent according to the user agent string received. Thus, various browsers have a feature to cloak or spoof their identification to force certain server-side content.

For example, the Android browser identifies itself as Safari (among other things) in order to aid compatibility. User agent sniffing is the practice of websites showing different or adjusted content when viewed with certain user agents.

An example of this is Microsoft Exchange Server 2003's Outlook Web Access feature. When viewed with Internet Explorer 6 or newer, more functionality is displayed compared to the same page in any other browsers.

Web browsers created in the United States, such as Netscape Navigator and Internet Explorer, previously used the letters U, I, and N to specify the encryption strength in the user agent string. Until 1996, when the United States government disallowed encryption with keys longer than 40 bits to be exported, vendors shipped various browser versions with different encryption strengths.

^ a b RFC 3261, SIP: Session Initiation Protocol, IETF, The Internet Society (2002) ^ RFC 7231, Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content, IETF, The Internet Society (June 2014) ^ Net news Article Format. Browser Versions Carry 10.5 Bits of Identifying Information on Average “, Electronic Frontier Foundation, 27 January 2010.

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I've been rejected until I come back with Netscape” ^ “Android Browser Reports Itself as Apple Safari”. ^ User Agent String explained: Android WebKit Browser”.

Mozilla/5.0 (Linux; U; Android 2.2; ends; HTC_DesireHD_A9191 Build/FRF91) Apple WebKit/533.1 (HTML, like Gecko) Version/4.0 Mobile Safari/533.1 ^ Emberton, Stephen. ^ “Chrome Phasing out Support for User Agent ".

The Disallow: / tells the robot that it should not visit any pages on the site. Especially malware robots that scan the web for security vulnerabilities, and email address harvesters used by spammers will pay no attention.

The rest of this page gives an overview of how to use / robots .txt on your server, with some simple recipes. Where to put it The short answer: in the top-level directory of your web server.

Usually that is the same place where you put your website's main index.html welcome page. Where exactly that is, and how to put the file there, depends on your web server software.

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Everything not explicitly disallowed is considered fair game to retrieve. To exclude all files except one This is currently a bit awkward, as there is no “Allow” field.

The easy way is to put all files to be disallowed into a separate directory, say “stuff”, and leave the one file in the level above this directory: However, both crawler types obey the same product token (user agent token) in robots .txt, and so you cannot selectively target either Google bot smartphone or Google bot desktop using robots .txt.

For sites that haven't yet been converted, the majority of crawls will be made using the desktop crawler. However, due to delays its possible that the rate will appear to be slightly higher over short periods.

Google bot was designed to be run simultaneously by thousands of machines to improve performance and scale as the web grows. Also, to cut down on bandwidth usage, we run many crawlers on machines located near the sites that they might crawl.

If that's not feasible, you can send a message to the Google bot team (however this solution is temporary). It's almost impossible to keep a web server secret by not publishing links to it.


If you want to prevent Google bot from crawling content on your site, you have a number of options. The bad bots you definitely want to avoid as these consume your CDN bandwidth, take up server resources, and steal your content.

Good bots (also known as web crawlers) on the other hand, should be handled with care as they are a vital part of getting your content to index with search engines such as Google, Bing, and Yahoo. Read more below about some top 10 web crawlers and user agents to ensure you are handling them correctly.

However, there are also issues sometimes when it comes to scheduling and load as a crawler might be constantly polling your site. This file can help control the crawl traffic and ensure that it doesn't overwhelm your server.

Google bot is obviously one of the most popular web crawlers on the internet today as it is used to index content for Google's search engine. Patrick Sexton wrote a great article about what a Google bot is and how it pertains to your website indexing.

One great thing about Google's web crawler is that they give us a lot of tools and control over the process. Bingo is a web crawler deployed by Microsoft in 2010 to supply information to their Bing search engine.

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Access pages from sites across the Web to confirm accuracy and improve Yahoo's personalized content for our users. DuckDuckGo is the Web crawler for DuckDuckGo, a search engine that has become quite popular lately as it is known for privacy and not tracking you.

These include hundreds of vertical sources delivering niche Instant Answers, DuckDuckGo (their crawler) and crowd-sourced sites (Wikipedia). They also have more traditional links in the search results, which they source from Yahoo!, Yandex and Bing.

Baidu spider is the official name of the Chinese Baidu search engine's web crawling spider. Mandelbrot is the web crawler to one of the largest Russian search engines, Yandex.

Soon Spider is the web crawler for, a leading Chinese search engine that was launched in 2004. Note: The Soon web spider does not respect the robots' exclusion standard, and is therefore banned from many websites because of excessive crawling.

Exact is a web crawler for Exiled, which is a search engine based out of France. Part of how this works on the Facebook system involves the temporary display of certain images or details related to the web content, such as the title of the webpage or the embed tag of a video.

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One of their main crawling bots is Face bot, which is designed to help improve advertising performance. As you probably know they collect information to show rankings for both local and international sites.

You generally don't want to block Google or Bing from indexing your site unless you have a good reason. Key CDN released a new feature back in February 2016 that you can enable in your dashboard called Block Bad Bots.

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