Andrew Norcross

Runs your RSS feed against the W3 RSS Validator and alerts you of any errors or warnings in a convenient dashboard widget. If either exist, a quick synopsis will explain the issues and provide a link to the W3 site for further explanation and possible fixes.

WP RSS Validator

Runs your RSS feed against the W3 RSS Validator.

Marios Alexandrou

Modifies RSS feeds so that they include pages and not just posts. Deactivating the plugin restores RSS feeds to their default state.
Including pages in your feed is particularly useful if you’re using WordPress as a CMS where pages represent a good portion of your content.
The <a href="https://infolific.com/technology/software-worth-using/include-pages-in-wordpress-rss-feeds/#pro-version" rel="nofollow ugc">pro version</a> (a lifetime license is less than $15) also allows you to:
<ol>
<li>Specify that ONLY pages are included in the feeds i.e. no posts.</li>
<li>Exclude/include posts and pages by ID.</li>
<li>Add custom post types such as WooCommerce products or Avada portfolios.</li>
</ol>

RSS Includes Pages

Some people say this plugin is useless, but they don't seem to be reading the description. If you want pages to be added to your existing feeds, this plugin will do that. No settings or configuration. Just activate and go.
Some additional features are in the pro version, but 30,000+ users find the free version useful enough to keep it active. You can't argue with the numbers! :-)



Adds Pages To Feeds Just Like It Says

Completely useless plugin. Only includes posts and pages into the RSS feed. For custom post types you have to pay $10. If you plan to make money with your plugins, please say so in the description so people don't waste their time.



Completely useless

Modifies RSS feeds so that they include pages and not just posts.

WP RSS Validator vs RSS Includes Pages