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.

xenice

Xenice SEO is a simple, fast, and lightweight SEO plugin designed to give you precise control over meta descriptions and keywords for every post, page, and taxonomy.
Unlike heavy SEO frameworks, Xenice SEO focuses on the essentials — helping search engines better understand your content without slowing down your website.

Xenice SEO

A lightweight SEO plugin that allows you to add meta description and keywords fields for posts, pages, categories, and custom post types.

Meta Keywords Generator vs Xenice SEO