Parth Panchal

SchemaNex allows you to easily add custom JSON-LD schema markup to posts, pages, and custom post types directly from the WordPress editor.
Features include:
<ul>
<li>Multiple schema blocks per post</li>
<li>Built-in JSON validation</li>
<li>AJAX schema validator</li>
<li>JSON formatting tools</li>
<li>Dynamic schema variables</li>
<li>Schema templates (FAQ, Service, Article, LocalBusiness, Breadcrumb)</li>
<li>Duplicate schema type detection</li>
<li>Yoast SEO / Rank Math conflict warnings</li>
<li>Gutenberg and Classic Editor support</li>
<li>CodeMirror-powered schema editor</li>
</ul>

SchemaNex

Add custom JSON-LD schema markup to posts, pages, and custom post types with validation, templates, and duplicate detection.

Tim van Iersel

Adds custom field to the post & pages editor for custom JSON-ld schema markup also known as structured data. The plugin also validates if the JSON is formated correctly. <a href="http://coderisk.com/wp/plugin/websitescanner-custom-schema/RIPS-8iSfZmxGFd" rel="nofollow ugc"></a>
Add your own JSON-ld on every page, post and custom post without the <code><script></code> to show your own custom Schema markup.
Works well with the following plugins:
<ul>
<li><a href="https://wordpress.org/plugins/remove-schema/" title="Remove Schema WordPress plugin" rel="ugc">Remove Schema</a></li>
</ul>
Usecases:
With the combination of the WordPress plugin it’s easy to overwrite the schema on a specific page. 
If a plugin like Yoast SEO or other plugin or theme that generates schema you can disable the schema and add your own custom schema to the page.

Websitescanner Custom Schema

Adds custom field to the post & pages editor for custom JSON-ld schema markup also known as structured data.

SchemaNex vs Websitescanner Custom Schema