Where to put it
The short answer: in the top-level directory of your web server.
The longer answer:
When a robot looks for the “/robots.txt” file for URL, it strips the path component from the URL (everything from the first single slash), and puts “/robots.txt” in its place.
For example, for “http://www.example.com/shop/index.html, it will remove the “/shop/index.html“, and replace it with “/robots.txt“, and will end up with “http://www.example.com/robots.txt”.
So, as a web site owner you need to put it in the right place on your web server for that resulting URL to work. Usually that is the same place where you put your web site’s main “index.html” welcome page. Where exactly that is, and how to put the file there, depends on your web server software.
Remember to use all lower case for the filename: “robots.txt“, not “Robots.TXT.
What to put in it
The “/robots.txt” file is a text file, with one or more records. Usually contains a single record looking like this:
User-agent: * Disallow: /cgi-bin/ Disallow: /tmp/ Disallow: /~joe/
In this example, three directories are excluded.
Note that you need a separate “Disallow” line for every URL prefix you want to exclude — you cannot say “Disallow: /cgi-bin/ /tmp/” on a single line. Also, you may not have blank lines in a record, as they are used to delimit multiple records.
Note also that globbing and regular expression are not supported in either the User-agent or Disallow lines. The ‘*’ in the User-agent field is a special value meaning “any robot”. Specifically, you cannot have lines like “User-agent: *bot*”, “Disallow: /tmp/*” or “Disallow: *.gif”.
What you want to exclude depends on your server. Everything not explicitly disallowed is considered fair game to retrieve. Here follow some examples:
To exclude all robots from the entire server
User-agent: * Disallow: /
To allow all robots complete access
User-agent: * Disallow:
(or just create an empty “/robots.txt” file, or don’t use one at all)
To exclude all robots from part of the server
User-agent: * Disallow: /cgi-bin/ Disallow: /tmp/ Disallow: /junk/
To exclude a single robot
User-agent: BadBot Disallow: /
To allow a single robot
User-agent: Google Disallow: User-agent: * Disallow: /
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:
User-agent: * Disallow: /~joe/stuff/
Alternatively you can explicitly disallow all disallowed pages:
User-agent: * Disallow: /~joe/junk.html Disallow: /~joe/foo.html Disallow: /~joe/bar.html