David Klhufek

This simple plugin adds useful buttons to the native WordPress HTML editor (Classic Editor).
Currently adds: 
h1, h2, h3, h4, h5, span, hr, nbsp, mox
The “mox” button adds a nice responsive CSS class which you can use to highlight pictures or other elements in your posts.
Note: This plugin works only with the Classic Editor. It does not support the new Gutenberg (Block Editor).
<h3>Compatibility</h3>
<ul>
<li>Requires the Classic Editor to be active. </li>
<li>Designed specifically for the HTML mode of the editor.</li>
</ul>

Quicktags for WP

This simple plugin adds useful buttons to the native WordPress HTML editor.

lloan

HTML Page Editor is a custom editor made for developers. It aims to help you write HTML within the Page editor. Simple plugin for a simple task.
Major features in HTML Page Editor include:
<ul>
<li>Code completion ‘Ctrl+Space’</li>
<li>A collection of themes to choose from for the post editor.</li>
<li>Save posts by pressing ‘Ctrl+S’</li>
<li>Cleaner page for creating and editing posts.</li>
<li>Full-screen visual editor for editing and previewing changes in posts. (F11)</li>
</ul>

HTML Page Editor

HTML Page Editor is a custom editor made for developers. It aims to help you write HTML within the Page editor. Simple plugin for a simple task.

Quicktags for WP vs HTML Page Editor