Robots.txt

It is great when search engines frequently visit your site and index your content but often there are cases when indexing parts of your online content is not what you want. For instance, if you have two versions of a page (one for viewing in the browser and one for printing), you'd rather have the printing version excluded from crawling, otherwise you risk being imposed a duplicate content penalty. Also, if you happen to have sensitive data on your site that you do not want the world to see, you will also prefer that search engines do not index these pages (although in this case the only sure way for not indexing sensitive data is to keep it offline on a separate machine). Additionally, if you want to save some bandwidth by excluding images, stylesheets and javascript from indexing, you also need a way to tell spiders to keep away from these items.
One way to tell search engines which files and folders on your Web site to avoid is with the use of the Robots metatag. But since not all search engines read metatags, the Robots matatag can simply go unnoticed. A better way to inform search engines about your will is to use a robots.txt file.

Syntax:

User-agent: *

disallow:
This will allow all search engine for spidering and will index all pages

NOINDEX prevents anything on the page from being indexed.
NOFOLLOW prevents the crawler from following the links on the page and indexing the linked pages.
NOIMAGEINDEX prevents the images on the page from being indexed but the text on the page can still be indexed.
NOIMAGECLICK prevents the use of links directly to the images, instead there will only be a link to the page.

What Is Robots.txt?

What Is Robots.txt?Robots.txt is a text (not html) file you put on your site to tell search robots which pages you would like them not to visit. Robots.txt is by no means mandatory for search engines but generally search engines obey what they are asked not to do. It is important to clarify that robots.txt is not a way from preventing search engines from crawling your site (i.e. it is not a firewall, or a kind of password protection) and the fact that you put a robots.txt file is something like putting a note “Please, do not enter” on an unlocked door – e.g. you cannot prevent thieves from coming in but the good guys will not open to door and enter. That is why we say that if you have really sen sitive data, it is too naïve to rely on robots.txt to protect it from being indexed and displayed in search results.
The location of robots.txt is very important. It must be in the main directory because otherwise user agents (search engines) will not be able to find it – they do not search the whole site for a file named robots.txt. Instead, they look first in the main directory (i.e. http://mydomain.com/robots.txt) and if they don't find it there, they simply assume that this site does not have a robots.txt file and therefore they index everything they find along the way. So, if you don't put robots.txt in the right place, do not be surprised that search engines index your whole site.
The concept and structure of robots.txt has been developed more than a decade ago and if you are interested to learn more about it, visit http://www.robotstxt.org/ or you can go straight to the Standard for Robot Exclusion because in this article we will deal only with the most important aspects of a robots.txt file. Next we will continue with the structure a robots.txt file.