Meta tags and search engine optimization
Meta tags are information for search engine bots in the <head> section of web page source code. There are three possible attributes for meta tags: http-equiv, content, and name. When discussing search engine optimization (SEO), the relevant meta tags are these name meta tags: the meta description tag and the meta keywords tag.
Bots used to give meta description and keywords tag content a lot of weight in determining search engine rankings. But because of the misuse of these meta tags, their value is debatable now. Their popularity has gone from "All you need are meta tags for search engine optimization" (which was never true) to the question, "Is anyone still using meta tags?"
Meta description tag
The meta description tag looks like this: <meta name="description" content="Page content description here.">
This meta tag is for webmasters to provide a summary of the web page content. Until Google was developed, meta description tag content influenced search engine results positions. Keyword density and relevance in meta description tags had the importance that they now do in web page content. Google, however, opted not to factor in meta description tag content, and other major search engines followed Google's example. The meta description tag is now generally believed to have SEO value only for some of the smaller search engines, but it's still often used.
This quote from Google Webmaster Central Blog  sums up Google's position on meta description tags: "...while accurate meta descriptions can improve clickthrough, they won't affect your ranking within search results."
Advantages of using the meta description tag
- It's believed to still be used by some lesser-known search engines. Having a meta description tag on each page may give those pages an SEO advantage with those search engines.
- It appears in search results with some search engines, especially if it contains the keyword searched for. (Search engines sometimes display part of the meta description tag content along with a page snippet, or just a snippet, depending on the search engine and what is searched for.) Well-written description tags that appear with search results may be better at attracting searchers to the page than snippets of text from the page.
Disadvantages of using the meta description tag
- Sometimes snippets are better at providing exactly what searchers are looking for than page summaries, especially if the page has a lot of content.
- Time spent working on meta description tags is time taken away from working on page content, which is more important.
How to use the meta description tag
- The lowest cut-off point for meta description tag content is about 150 words, so 150 characters (including spaces) is a good maximum length to use.
- Write a unique description or summary for each page.
- Make each description concise and accurate, with information that adds to the page title and tells searchers what they'll find on the page.
- Use grammatically correct sentences and punctuation.
- Include keywords, but as in page content, work them in naturally.
Meta keywords tag
The meta keywords tag looks like this: <meta name="keywords" content="keyword1,keyword2,keyword3">
The meta keywords tag was popular in the 1990s, when search engines used its contents, among other factors, to determine search results. However, many webmasters abused the meta keywords tag by stuffing it with keywords that weren't necessarily on the web page, sometimes repeating the keywords to try to improve the page ranking. Moreover, some webmasters put deliberately misleading keywords in it to attract more traffic. Between about 1997 and 2002, most major search engines discontinued support of the meta keywords tag. Only Inktomi (now owned by Yahoo) continued to support it.
The general consensus is that the meta keywords tag has little to no value any more. However, Yahoo still recommends its use  although it's believed that Yahoo gives it very little weight.
Advantages of using the meta keywords tag
- It may carry a little weight with Yahoo.
- It may be a factor with some lesser-known search engines.
- If you list misspellings of words that you use on the page, it may help your page appear in Yahoo search results for those misspellings.
Disadvantages of using the meta keywords tag
- When you use it, you're telling your competitors exactly what keywords you're optimizing each page for. Competitors can take those lists that you carefully crafted and optimize their own sites for the same keywords.
- Time spent working on meta keyword tags is time taken away from optimizing your site for those keywords, which is more important.
How to use the meta keywords tag
If you use the meta keywords tag:
- List the keywords and keyword phrases that you're optimizing the page for in the meta keywords tag for that page.
- Include misspellings and alternative spellings of words on the web page.
- Limit your list to keywords that the page is optimized for along with the above variations; avoid keyword spamming.
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