Search engines pay attention to some tags, and none to others. Remember when the ‘keywords’ meta tag mattered? Ah, the good old days.
John Mueller placed a useful post from Zurich on the Webmaster Central blog at Google, where he delves into the issue of meta tags. Back in the day, meta tags like ‘keywords’ helped webmasters get their sites indexed appropriately.
It took next to no time for spammers to start clogging ‘keywords’ to the point where they became useless. As Mueller reminded everyone in an answer to a comment, Google isn’t looking at them for indexing purposes:
(W)e generally ignore the contents of the “keywords” meta tag. As with other possible meta tags, feel free to place it on your pages if you can use it for other purposes – it won’t count against you.
Plenty of tags do work favorably for pages, as do Sitemaps, which enjoy support from Google, Yahoo, and Microsoft. Meta tags can control robot behavior, or in the case of an individual crawler like Google’s Googlebot, affect a single robot’s actions with certain directives like meta name=robots or name=googlebot:
Google understands the following values (when specifying multiple values, separate them with a comma):
noindex: prevents the page from being indexed (see “Block or remove pages using meta tags”)
nofollow: don’t follow links from this page when looking for new pages to crawl (also see “Block or remove pages using meta tags”)
nosnippet: don’t show a snippet of this page when displaying it in the search results (see “Prevent or remove snippets”)
noodp: don’t use text from ODP (The Open Directory Project a.k.a. dmoz.org) to generate a title or snippet for this page (see “How do I change my site’s title and description?”)
noarchive: don’t display a “Cached” link for this page in the search results (see “Prevent or remove cached pages”)
unavailable_after:[date]: remove this page from the search results after the specified date and time (see “Robots Exclusion Protocol: now with even more flexibility”)
Mueller noted the default rule is “index, follow” when this meta tag is not in place on a page, or if it is not targeted to the visiting spider when it arrives.
