HTML embed

The HTML embed feature lets you embed any HTML snippet in your content. The feature is meant for more advanced users who want to directly interact with HTML fragments.

# Demo

Use the HTML embed toolbar button in the editor below to see the plugin in action. Click the “Preview editor data” button under the editor to preview the editor content, including the embedded HTML.

# Additional feature information

This feature lets you embed any HTML code and bypass CKEditor 5’s filtering mechanisms. You can use it to enrich content produced by CKEditor 5 with fragments of HTML that are not supported by any other CKEditor 5 feature.

Some examples of content that you can embed thanks to the HTML embed feature:

• Analytics code (that usually requires embedding <script> elements).
• Social page widgets (that also require embedding <script> elements).
• Content embeddable by <iframe> elements.
• HTML media elements such as <audio> and <video>.
• HTML snippets produced by external tools (for example, reports or charts).
• Interactive content that requires a combination of rich HTML and scripts.

We recommended using the media embed feature for embeddable media that this feature supports. You can use the HTML embed feature to handle the remaining content.

# Installation

After installing the editor, add the feature to your plugin list and toolbar configuration:

import { ClassicEditor, HtmlEmbed } from 'ckeditor5';

ClassicEditor
    .create( document.querySelector( '#editor' ), {
        plugins: [ HtmlEmbed, /* ... */ ],
        toolbar: [ 'htmlEmbed', /* ... */ ],
    } )
    .then( /* ... */ )
    .catch( /* ... */ );

# Configuration

# Content previews

The feature is by default configured to not show previews of the HTML snippets. You can enable the previews by setting the config.htmlEmbed.showPreviews option to true.

However, by showing previews of the embedded HTML snippets, you expose the users of your system to the risk of executing malicious JavaScript code inside the editor. Therefore, it is highly recommended to plug in some HTML sanitizer that will strip the malicious code from the created snippets before rendering their previews. You can plug in the sanitizer by defining the config.htmlEmbed.sanitizeHtml option.

ClassicEditor
    .create( document.querySelector( '#editor' ), {
        plugins: [ HtmlEmbed, /* ... */ ],
        toolbar: [ 'htmlEmbed', /* ... */ ],
        htmlEmbed: {
            showPreviews: true,
            sanitizeHtml: ( inputHtml ) => {
                // Strip unsafe elements and attributes, for example:
                // the `<script>` elements and `on*` attributes.
                const outputHtml = sanitize( inputHtml );

                return {
                    html: outputHtml,
                    // true or false depending on whether the sanitizer stripped anything.
                    hasChanged: true
                };
            }
        }
    } )
    .then( /* ... */ )
    .catch( /* ... */ );

Currently, the feature does not execute <script> tags so the content that requires executing JavaScript to generate a preview will not show in the editor. However, other JavaScript code, for example, used in on* observers and src="javascript:..." attributes will be executed. You still need to enable the sanitizer.

Read more about the security aspect in the next section.

# Security

If you configure the HTML embed feature to show content previews, the HTML that the user inserts into the HTML embed widget is then rendered back to the user. **If the HTML was rendered as-is, the browser would execute any JavaScript code included in these HTML snippets in the context of your website.

This, in turn, is a plain security risk. The HTML provided by the user might be mistakenly copied from a malicious website. It could also end up in the user’s clipboard (as it would usually be copied and pasted) by any other means.

You can instruct some advanced users to never paste HTML code from untrusted sources. However, in most cases, it is highly recommended to secure the system by configuring the HTML embed feature to use an HTML sanitizer and, optionally, by setting strict Content Security Policy (CSP) rules.

# Sanitizer

The config.htmlEmbed.sanitizeHtml option allows plugging an external sanitizer.

Some popular JavaScript libraries that you can use include sanitize-html and DOMPurify.

The default settings of these libraries usually strip all potentially malicious content including <iframe>, <video>, or similar elements and JavaScript code coming from trusted sources. You may need to adjust their settings to match your needs.

# CSP

In addition to using a sanitizer, you can use the built-in browser mechanism called Content Security Policy. By using CSP you can let the browser know the allowed sources and means to execute JavaScript code and include other resources such as style sheets, images, and fonts.

# Related features

CKEditor 5 supports a wider range of embed and code features, including:

• Media embed – Insert embeddable media such as YouTube or Vimeo videos and tweets into your rich text content.
• Code blocks – Insert longer, multiline listings of pre-formatted code with a programming language assigned.
• General HTML Support – Enable HTML features (elements, attributes, classes, styles) that are not supported by other dedicated CKEditor 5 plugins.

# Common API

The HtmlEmbed plugin registers:

• The UI button component ('htmlEmbed').
• The 'htmlEmbed' command implemented by HtmlEmbedCommand.

You can execute the command using the editor.execute() method:

// Inserts an empty HTML embed.
editor.execute( 'htmlEmbed' );

// Inserts an HTML embed with some initial content.
editor.execute( 'htmlEmbed', '<b>Initial content</b>.' );

// Updates the content of a selected HTML embed.
editor.execute( 'htmlEmbed', '<b>New content.</b>' );

# Contribute

The source code of the feature is available on GitHub at https://github.com/ckeditor/ckeditor5/tree/master/packages/ckeditor5-html-embed.