Devtard

This plugin automatically searches posts when they are published/imported/saved and adds new taxonomy terms (tags by default) if term names or related keywords from a user-created keyword list are found.
<h4>Features</h4>
<ul>
<li>Compatible with several post import plugins (<a href="https://wordpress.org/plugins/automatic-post-tagger/faq/" rel="ugc">FAQ #4</a>)</li>
<li>Supports custom taxonomies and post types; for example, APT is able to categorize posts (<a href="https://wordpress.org/plugins/automatic-post-tagger/faq/" rel="ugc">FAQ #6</a>), add tags/categories to WooCommerce products (<a href="https://wordpress.org/plugins/automatic-post-tagger/faq/" rel="ugc">FAQ #7</a>)</li>
<li>Supports UTF-8 characters, non-Latin and logographic alphabets (<a href="https://wordpress.org/plugins/automatic-post-tagger/faq/" rel="ugc">FAQ #5</a>), including Arabic, Chinese, Cyrillic etc.</li>
<li>Bulk tagging tool (with a scheduler) for processing multiple posts</li>
<li>Import/Export tools (CSV & JSON format support)</li>
<li>Configuration groups with custom rules for selected keyword sets; wildcard (regex) support for related keywords</li>
</ul>
See <a href="https://wordpress.org/plugins/automatic-post-tagger/screenshots/" rel="ugc">Screenshots</a> and <a href="https://wordpress.org/plugins/automatic-post-tagger/faq/" rel="ugc">FAQ</a> for more information.

Automatic Post Tagger

Adds relevant taxonomy terms to posts using a keyword list provided by the user.

pywebdev

AutoTag is plugins to auto get tag from content, title using search engine (google, bing, stackoverflow) and text processing from content of post

Webdev AutoTag

AutoTag is plugins to auto get tag from content, title using search engine (google, bing and stackoverflow)

Automatic Post Tagger vs Webdev AutoTag