Meta tags are HTML elements used to provide some metadata (data about data) about a web page. They are overwhelmingly used for search engine crawlers as opposed to for users, thus they are often viewed as vital component of search engine optimization (SEO). Meta tags should reside in the HEAD portion of your HTML code. Some of the meta tags, particularly those important in SEO work.
Keywords
This is one of the most heavily used meta tag for SEO purposes. You should provide a few keywords relevant to the particular page, and only the relevant ones only. You should not include keywords only because they are popular, as the long term potential negative effects of keyword stuffing far outweighs any short term benefits you may gain.
<meta name="keywords" content="cooking, boiling, egg, recipe" />
Robots
As the name suggests, this tag is not for humans. Instead, it provides some instructions for search engine crawlers. Some possible values are as follows.
- index: Recommends the search engine to include this page from its index. This can be considered a little bit useless, as normally the crawler is out to index your page anyway. It does not hurt to include it, however.
- noindex: Recommend the search engine to exclude this page from its index.
- follow: Recommend the search engine crawler to follow all links found on this page. Like index, this can also be considered a little bit useless, as it is a normal function of a crawler regardless of this instruction.
- nofollow: Recommends the search engine crawler to not follow any links found on this page.
- noarchive: Recommends the search engine to not cache a copy of the page in its archive.
- nosnippet: Recommends the search engine to not cache a copy of the page in its archive (this portion is same as noarchive), and also recommends the search engine to not display any snippets of the page’s content on the search results page. This may be useful if you are under strict intellectual property limitations that none of the page’s content can be displayed anywhere other than your site.
- noodp: Recommends the search engine to not place the Open Directory Project description of your page next to the search results.
- none: This is equivalent to “noindex, nofollow”.
Should you wish to use more than one value, use a comma to separate them. Spaces are ignored, so they make no difference. Also, the values found in the robots tag are processed without case sensitivity (eg. “noindex” and “NoIndex” are considered the same). Some examples are listed below.
<meta name="robots" content="none" /> <meta name="robots" content="index, nofollow" /> <meta name="robots" content="nofollow, nosnippet, noodp" />
Revisit-After
This allows you to recommend the crawler to return to the same page for another round of indexing. Like most other tags, this is just a recommendation to the search engines and their crawlers, so you should not expect this to be followed exactly. Along the same lines, you should also note that most major search engines do not obey this meta tag at all; they will re-index your pages when they deem necessary.
<meta name="revisit-after" content="15 days" />
Description
The description meta tag provides a space for you to provide a very brief description of the current page. This is not a recommendation to the crawlers like the ones mentioned thus far. This information is used by some search engines to display as the brief description on the search results page, so it is important for you to provide something concise and to-the-point so that users will know whether your page will give them the information they want. If you are unsure what to put in here, just put in whatever you have for the title tag (not discussed in this article) for that page, as shown in the example below.
<meta name="description" content="How to boil an egg" />
Content-Type
This informational entry describes the content of the page. There are too many possibilities to list all possible values for content-type, but the examples below should illustrate the usage.
Example 1: Notes the page is a HTML page, using the iso-8859-1 character set.
<meta http-equiv=Content-Type content="text/html; charset=iso-8859-1" />
Example 2: Notes the page is actually a .xls file (Microsoft Excel spreadsheet), so the user should use the appropriate program to handle it instead of trying to interpret it as HTML.
<meta http-equiv=Content-Type content="application/xls" />
Content-Language
This provides information on the language your page is written in. The following three examples are for American English, Traditional Chinese, and German, respectively.
<meta http-equiv="content-language" content="en-us" /> <meta http-equiv="content-language" content="zh-tw" /> <meta http-equiv="content-language" content="de" />
The two meta tags below are not really related to SEO, but it might be useful to know them in any case.
Generator
On the surface, it tells of the software package used to generate the page, particularly if the software package uses any proprietary stuff in the code. However, since HTML code is mostly standardized, this tag is not really useful even though it is still very popular as many software packages still make use of them. It may be cynical to say this tag is no more than advertisement for the software packages.
<meta name="generator" content="HTML Software v0.1.2.3" />
Pragma
The only option that I know of for the pragma is no-cache, which recommends the visitors’ browsers to not cache this page locally. This is useful if you have a page with content changes very frequently (ie. more than once for each visitor within the same visit) while the URL does not change. Try this meta tag if your users complain that they are always seeing stale data but you cannot reproduce the experience on other machines.
<meta http-equiv="pragma" content="no-cache" />
Additional Information
Author, contact_addr, and copyright meta tags allow you to provide some information about the page. They are purely informational and do not provide any recommendations to the crawlers.
<meta name="copyright" content="Copyright © 2008 C. Peter Chen" /> <meta name="author" content="C. Peter Chen" /> <meta name="contact_addr" content="email@me.here" />