After studying the title tag, we are going now to look at the meta description tag.
This field is usually a brief summary of the page. Regarding search engines, the description has also to contain the main keywords to better classify the post.

Structure Overview

The general structure of the previous post was:

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add_action ( 'wp_head', 'my_seo_title');
 
function my_seo_title function () {
    // Function to print the title
}

We will now add a function to manage description. We take the opportunity to combine our SEO functions:

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 add_action ( 'wp_head', 'my_seo_features', 1);
 
function my_seo_title function () {
    // Function to display the title
}
 
function my_seo_description function () {
    // Function to display the description
}
 
function my_seo_features function () {
    my_seo_title ();
    my_seo_description ();
}

About add_action, we add the parameter ’1′. This parameter will put our function at the beginning of the list of actions to perform in wp_head(). In this way, our tags are located at the top of the header, rather than the bottom as in the previous post.

Generate description tag

Before starting, we have to define the content of this tag, for each case. For page ‘Category’, the answer is simple, since the categories have a description. But in the case of posts, archives, tags, what to do?

The following table summarizes what we can do:

Page Type Description
1. Home blog description
2. Post or page The excerpt of the post or the first few lines
3. Category The description of the category
4. Tags The summary of the first item of the list of posts
5. Research
6. Archives blog description

Why these choices?

  • Lines 1 and 3, we have a description, there is nothing to do
  • Line 2, we can estimate that the summary of the post gives a good overview of the post itself,
  • Lines 4 and 5, we can also consider that the posts corresponding to a tag or a search results, look more or less, similar. Therefore, the summary of the first article can be significant,
  • Line 6 (archives), it seems difficult (even dangerous) to build a description based on several posts that can be very different.

How to collect information about the articles? Using global variables post and posts, which are generated by WordPress before loading pages.

We obtain the following PHP code:

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function my_seo_description() {
  global $post, $posts;
 
  if ( (is_single() || is_page()) ) {
      $page_description = get_description($post);
  }
  elseif (is_category()) {
      $page_description = category_description();
  }
  elseif ( is_tag() ) {
      $page_description = get_description(current($posts[0]));
  }
  elseif (is_date()) {
      $page_description = get_bloginfo('description');
  }
  elseif (is_search()) {
      if (sizeof($posts) > 0) {
          $page_description = get_description(current($posts[0]));
	}
      else {
          $page_description = get_bloginfo('description');
	}
  } else { /* is_home normalement */
      $page_description = get_bloginfo('description');
  }
  if ($page_description != '') {
      $page_description = htmlspecialchars(stripslashes(strip_tags(str_replace("\n", '', $page_description))));
      echo '<meta name="description" value="'.$page_description.'">'."\n";
  }
}

Some explanations:

  • Line 5: a single post is displayed, the global variable $post is available,
  • Lines 11 and 18, we have a list of posts to display. The global variable $posts is available. With the function current(), we get the first element (post),
  • In other cases, we retrieve the description of the blog,
  • At the end, we try to filter as much as possible, the content of the description to avoid any incident during the display.

The get_description() can be:

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 function get_description($current_post) {
  $max_length = 200;
  $string = '';
  // If post has an excerpt?
  if ($current_post->post_excerpt != '') {
      $string = wp_html_excerpt ( $current_post->post_excerpt, $max_length);
  }
  else {
      // No excerpt, try to find the <!--more--> tag, or cut content.
      $char_count = min( $max_length, strpos($current_post->post_content, '<!--more-->')-1);
 
      // Extract description from the content
      $string = wp_html_excerpt ( $current_post->post_content, $char_count);
  }
  return ($string);
}

Some explanations:

  • A description field must not exceed 100 to 200 characters ($ max_length),
  • If the author has entered an excerpt, we use it,
  • Otherwise, we retrieve the content of the post, we cut at the <!--more-->, if it exists, or at most to 200 characters.

[attachment title="Download the complete code (including the sources of the previous post) from here:" titletag=p]

Conclusion

Our SEO Service is almost complete. We fill the fields title, robots meta, and description. We will see in a next post, how to fill in the meta keywords.

Other posts of the serie

  1. Développer vos propres fonctions SEO avec WordPress: les mots-clés - 19 February 2009
  2. Développer ses propres fonctions SEO avec WordPress: la description (This post) - 12 February 2009
  3. Développez vos propres fonctions SEO avec WordPress: le titre - 5 February 2009
  4. 6 plugins SEO pour WordPress - 5 January 2009