Meta tags are placed in the page header and are not shown to the ordinary visitor. Search engines currently ignore them in many cases. It is advisable to use only the most necessary meta tags so that the size of the page is not increased needlessly.
Useful meta tags are content-type and content-language, which specify the encoding and language of the page. They help the text on the page to be displayed and indexed correctly. Both tags should be placed right at the beginning of the header (head). Another one in use is description, which briefly describes the content of the page. Some search engines show it as the description of the link in search results. The keywords meta tag is sometimes still used; it should contain several keywords separated by commas that characterize the content of the website. It was also used to enter keywords without diacritics for languages such as Czech. Every page should have unique content in the description and keywords tags, no longer than 256 characters.
Meta tags placed in the page header might look like this, for example:
<meta http-equiv="content-type" content="text/html; charset=utf-8"> <meta http-equiv="content-language" content="cs"> <meta name="keywords" content="klíč,klic,klicova fraze"> <meta name="description" content="Stručný popis tématiky stránky.">
Meta tags can also be used to specify the author of the page, a contact for the author and so on. They are sometimes also used to give commands to a crawler, for example like this:
<meta name="robots" content="noindex,nofollow">
With the robots tag you can forbid search engine robots that support it from indexing the page and following links from it. If this tag is missing, everything is allowed by default.
Open Graph
Recently, the meta tags used by the Open Graph protocol from Facebook have also come to the forefront. They are meant mainly to help load suitable data when pages are shared. An example might look like this:
<meta property="og:title" content="Název stránky"> <meta property="og:description" content="Popis stránky"> <meta property="og:site_name" content="Název-webu.cz"> <meta property="og:url" content="http://nazev-webu.cz/stranka/"> <meta property="og:image" content="http://nazev-webu.cz/obrazek.jpg"> <meta property="og:type" content="article">
Because the Open Graph protocol is not yet a valid standard, the permanent URL (og:url) and the related image (og:image) can be replaced with valid link tags with the rel attribute, like this:
<link rel="canonical" href="http://nazev-webu.cz/stranka/"> <link rel="image_src" href="http://nazev-webu.cz/obrazek.jpg">
Recently the previewimage tag has also started to be used:
<link rel="previewimage" href="http://nazev-webu.cz/obrazek.jpg">