Installation

1. Zip the eqneditor folder from the download below and upload it through Plugins → Add New → Upload Plugin, or copy the folder into /wp-content/plugins/.
2. Activate CodeCogs Equation Editor under Plugins.
3. If your site uses the block editor, install and activate the official Classic Editor plugin, or add equations inside a Classic block. The fx button attaches to the Classic Editor's toolbar, which the block editor's own blocks do not have.
4. Give the plugin your licence key, below. Then open a post: the fx button is on the toolbar.

Your licence key

The plugin has no settings page; it reads its configuration from JavaScript globals set in the admin pages. The simplest place to set them is a small must-use plugin — a file in /wp-content/mu-plugins/:

<?php
// wp-content/mu-plugins/eqneditor-config.php
add_action( 'admin_head', function () {
    echo '<script>'
       . 'window.eqneditorServer  = "fxtex.codecogs.com";'
       . 'window.eqneditorLicence = "fx_pk_your-key-here";'
       . 'window.eqneditorDesign  = { colour: "#0f7a4d" };'   // optional
       . '</script>';
} );

Customise and download

Make the equation editor your own: choose what it shows, drag panels from More panels into up to three toolbar rows, and pick a colour and sizes. The preview is the real WordPress page, rebuilt as you go. Then add your licence key and download it: an example.html with a page of equations to edit, loading everything it needs from fxplugins.codecogs.com.

Your design

The option that gives WordPress this design — it is already in the download. Leave it out and the editor uses the standard design.

Complete example

The whole of the page running above: a simple, complete HTML page that loads WordPress and the plugin. Every file comes from fxplugins.codecogs.com, so it works as it is — put in your own licence key. (Keys are shortened here.)

Equations in your posts

The author chooses MathML or an SVG image in the dialog. The plugin lets MathML through WordPress's content filter, so Authors and Contributors can save it too — without that, WordPress strips <math> from the posts of anyone who cannot post unfiltered HTML.

For MathML to display at its best, your theme needs one stylesheet. Add it to the theme's header, or with wp_enqueue_style:

add_action( 'wp_enqueue_scripts', function () {
    wp_enqueue_style( 'fxtex', 'https://fxtex.codecogs.com/fxtex.css' );
} );