How does robots.txt differ from the ROBOTS META tag?

robots.txt is used to tell robots which parts of a site should not be visited, whereas the ROBOTS META tag tells a robot how to treat a specific page.

from The Web Robots Pages:
The ROBOTS META tag allows HTML authors to indicate to visiting robots if a document may be indexed, or used to harvest more links. No server administrator action is required.

Note that currently only a few robots implement this.

In this simple example:

<META NAME="ROBOTS" CONTENT="NOINDEX, NOFOLLOW">

a robot should neither index this document, nor analyse it for links.

Full details on how this tags works is provided:

• Web Server Administrator's Guide to the Robots META tag
• HTML Author's Guide to the Robots META tag

• The original notes from the May 1996 IndexingWorkshop

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