Bouzid Nazim Zitouni

PSMAN

TagGator lets you build a keyword list and apply matching tags to all your posts in one click.
How it works:
<ol>
<li>Enter your tag words in the Tag List — one per line, or comma-separated. Each word is both the tag name and the keyword searched for.</li>
<li>Configure matching options (case-sensitive, whole words, minimum occurrences).</li>
<li>Click Preview to see what would be tagged, or Bulk Tag All Posts to apply tags immediately.</li>
<li>Use Remove Unmatched Tags to clean up stale tags if you update your list.</li>
</ol>
Example tag list:
<pre><code>JavaScript, PHP, Python
WordPress, Gutenberg
Node.js, React, Vue
</code></pre>
A post containing “JavaScript” receives the “JavaScript” tag. Tags are only applied when the minimum match count is met, so you stay in control.
Features:
<ul>
<li>Flat tag list — every word is both tag and keyword, no complex syntax</li>
<li>Case-sensitive or case-insensitive matching</li>
<li>Whole-word or substring matching</li>
<li>Minimum match count in body and/or title</li>
<li>Enable/disable tagging per post type</li>
<li>Choose which taxonomy to tag with per post type</li>
<li>Preview before committing — no surprises</li>
<li>Remove Unmatched Tags cleans up only plugin-applied tags, never manually added ones</li>
<li>Tagging history in the post editor sidebar</li>
<li>No external dependencies, no tracking, no telemetry</li>
</ul>
Looking for more?
<a href="http://codecanyon.net/item/taggator-pro-wordpress-auto-tagging-plugin/1725033?ref=AngryByte" rel="nofollow ugc">[TagGator Pro]</a> adds:
<ul>
<li>Auto-tag posts on save — no manual bulk runs needed</li>
<li>Keyword-to-tag synonym mapping (one tag, many keywords per line)</li>
<li>Exclude posts by ID, category, or author</li>
<li>Per-post and per-user exclusion controls</li>
<li>Priority support</li>
</ul>

TagGator

Bulk-tag your posts by matching keywords against content. Simple, fast, and free.

dangrossman

The Calais Archive Tagger plugin automatically goes through your archives and tags every post you’ve written. The plugin uses the Open Calais API to perform semantic analysis of your post text and suggest tags. If a post already contains a suggested tag, that tag isn’t added, but other new tags found are. It takes about 5 minutes to tag 200 posts.
This plugin requires PHP 5 and the cURL library (both of which are available on most web hosts).
Also see <a href="https://wordpress.org/extend/plugins/calais-auto-tagger/" rel="ugc">WP Calais Auto Tagger</a> for suggesting tags as you write new posts.

WP Calais Archive Tagger

Goes through your archives and adds tags to your posts based on semantic analysis.

TagGator vs WP Calais Archive Tagger