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.

Joris van Montfort

Are you using HTML code in your Contact Form 7 forms and email bodies? Ace syntax highlighting enhanches the Contact Form 7 backend and makes it easy to code HTML for complex forms.

Contact Form 7 Syntax Highlighting

Works like a charm

Perfect!

Adds syntax higlighting to the Contact Form 7 admin screens. Requires the Contact Form 7 plugin.

Quicktags for WP vs Contact Form 7 Syntax Highlighting