jp2112

Show Archive Descriptions is a plugin that displays the description for a category on that category’s first archive page. It does the same for tags and author archives.
<h3>If you need help with this plugin</h3>
If this plugin breaks your site or just flat out does not work, please go to <a href="https://wordpress.org/plugins/show-archive-descriptions/#compatibility" rel="ugc">Compatibility</a> and click “Broken” after verifying your WordPress version and the version of the plugin you are using.
Then, create a thread in the <a href="https://wordpress.org/support/plugin/show-archive-descriptions" rel="ugc">Support</a> forum with a description of the issue. Make sure you are using the latest version of WordPress and the plugin before reporting issues, to be sure that the issue is with the current version and not with an older version where the issue may have already been fixed.
Please do not use the <a href="https://wordpress.org/support/view/plugin-reviews/show-archive-descriptions" rel="ugc">Reviews</a> section to report issues or request new features.
<h4>Features</h4>
<ul>
<li>Display archive descriptions (category, tag, author) with your custom text</li>
<li>Create custom titles</li>
</ul>

Show Archive Descriptions

Display category, tag and author descriptions on the appropriate archive pages.

techphernalia

This plugin helps your SEO by adding meta keywords tag to each page, post, archive (category, tag, date, day and year). 
Now it also allows you to specify common keywords to be included on every web page. Plugin from one of the best coder <a href="https://www.techphernalia.com/" rel="nofollow ugc">Durgesh Chaudhary</a>. 
For any support just leave your question at our <a href="https://www.techphernalia.com/meta-keywords-generator/" rel="nofollow ugc">Meta Keywords Generator</a> page.
Uses Title, Description, Categories, tags, Compulsary keywords (provided by you in setting) for keywords generation. Uses content after striping short codes and short tags for generation of description.
Reduces manual work of adding them manually.
Now more efficient by allowing you to add one time master keyword list.
A big Thanks to Omer Barlas for suggesting to change text box to textarea for better readability.

Meta Keywords Generator

Adds Meta keywords and Description to each and every page, post, archive.

Show Archive Descriptions vs Meta Keywords Generator