Tenseg LLC

This plugin will look at another site you specify whenever a 404 error occurs and check if the requested path is there. If the path is found, it will redirect there rather than show the WP 404 page.
This is particularly useful to silently redirect over to an archival copy of a website when a major redesign has been done.
More information about this plugin can be found <a href="https://www.tenseg.net/software/404sitechecker" rel="nofollow ugc">on its homepage</a>.

404 Site Checker

When you get a 404 this will check the requested path at a site you define and redirect there if found rather than showing the 404.

Jesin A

WordPress offers inbuilt support for custom 404 pages on all themes. But what about custom pages for other common errors like 401 and 403? You end up seeing a bland error page of the Web Server.
With this plugin you can easily create custom 401 and 403 error pages with any theme without writing a single line of code!!! And the best part is that you set it and forget it. Yes, you don’t have to do any changes even if you change themes. The heading and text you want on 401 and 403 error pages are displayed on the currently active theme.
<h4>Further Reading</h4>
<ul>
<li><a href="https://websistent.com/wordpress-custom-403-401-error-page/" rel="nofollow ugc">Create WordPress 401 and 403 error pages</a> WITHOUT using this plugin</li>
<li>The <a href="https://websistent.com/wordpress-plugins/custom-error-pages/" rel="nofollow ugc">Custom Error Pages Plugin</a> official homepage.</li>
</ul>

Custom Error Pages

Create custom 401 and 403 error pages with any WordPress theme without writing a single line of code, set it up and forget it.

404 Site Checker vs Custom Error Pages