ZanclOn

This plugin adds extra details to the information present in the posts exposed by the wordpress REST API.
For example:
<ul>
<li>terms and taxonomy</li>
<li>meta</li>
<li>connections between posts (wp-posts-to-posts)</li>
</ul>

WP Extended Data to REST API

This plugin adds extra details to wordpress REST API.

Jeff Starr

Does one thing: Completely disables the WordPress REST API for visitors who are not logged into WordPress. No configuration required.
Important: This plugin completely disables the WP REST API for visitors who are NOT logged in to WordPress. So not recommended if your site needs the WP REST API for any non-logged users.
👉 The fast, simple way to prevent abuse of your site’s REST/JSON API 
👉 Protects your site’s REST data from all non-logged users and bots 
👉 Uses only 4KB of code, so super lightweight, fast, and effective
<h3>Features</h3>
<ul>
<li>Disable REST/JSON for visitors (not logged in)</li>
<li>Disables REST header in HTTP response for all users</li>
<li>Disables REST links in HTML head for all users</li>
<li>100% plug-and-play, set-it-and-forget solution</li>
</ul>
How does it work?
This plugin completely disables the WP REST API unless the user is logged into WordPress.
<ul>
<li>For logged-in users, WP REST API works normally</li>
<li>For logged-out users, WP REST API is disabled</li>
</ul>
What happens if logged-out visitor makes a JSON/REST request? They will get only a simple message:
<pre><code>rest_login_required: REST API restricted to authenticated users.
</code></pre>
This message may customized via the filter hook, <code>disable_wp_rest_api_error</code>. Check out <a href="https://wordpress.org/support/topic/not-entirely-for-non-techies/#post-12014965" rel="ugc">this post</a> for an example of how to do it.
<h3>Privacy</h3>
This plugin does not collect or store any user data. It does not set any cookies, and it does not connect to any third-party locations. Thus, this plugin does not affect user privacy in any way. If anything it improves user privacy, as it protects potentially sensitive information from being displayed/accessed via REST API.
Disable WP REST API is developed and maintained by <a href="https://x.com/perishable" rel="nofollow ugc">Jeff Starr</a>, 15-year <a href="https://plugin-planet.com/" rel="nofollow ugc">WordPress developer</a> and <a href="https://books.perishablepress.com/" rel="nofollow ugc">book author</a>.
<h3>Support development of this plugin</h3>
I develop and maintain this free plugin with love for the WordPress community. To show support, you can <a href="https://monzillamedia.com/donate.html" rel="nofollow ugc">make a donation</a> or purchase one of my books:
<ul>
<li><a href="https://wp-tao.com/" rel="nofollow ugc">The Tao of WordPress</a></li>
<li><a href="https://digwp.com/" rel="nofollow ugc">Digging into WordPress</a></li>
<li><a href="https://htaccessbook.com/" rel="nofollow ugc">.htaccess made easy</a></li>
<li><a href="https://wp-tao.com/wordpress-themes-book/" rel="nofollow ugc">WordPress Themes In Depth</a></li>
<li><a href="https://books.perishablepress.com/downloads/wizards-collection-sql-recipes-wordpress/" rel="nofollow ugc">Wizard’s SQL Recipes for WordPress</a></li>
</ul>
And/or purchase one of my premium WordPress plugins:
<ul>
<li><a href="https://plugin-planet.com/bbq-pro/" rel="nofollow ugc">BBQ Pro</a> – Blazing fast WordPress firewall</li>
<li><a href="https://plugin-planet.com/blackhole-pro/" rel="nofollow ugc">Blackhole Pro</a> – Automatically block bad bots</li>
<li><a href="https://plugin-planet.com/banhammer-pro/" rel="nofollow ugc">Banhammer Pro</a> – Monitor traffic and ban the bad guys</li>
<li><a href="https://plugin-planet.com/ga-google-analytics-pro/" rel="nofollow ugc">GA Google Analytics Pro</a> – Connect WordPress to Google Analytics</li>
<li><a href="https://plugin-planet.com/head-meta-pro/" rel="nofollow ugc">Head Meta Pro</a> – Ultimate Meta Tags for WordPress</li>
<li><a href="https://plugin-planet.com/simple-ajax-chat-pro/" rel="nofollow ugc">Simple Ajax Chat Pro</a> – Unlimited chat rooms</li>
<li><a href="https://plugin-planet.com/usp-pro/" rel="nofollow ugc">USP Pro</a> – Unlimited front-end forms</li>
</ul>
Links, tweets and likes also appreciated. Thank you! 🙂

Disable WP REST API

while the plugin si deadsimple and very low resource impact, keep in mind that there are plugins that need the rest to work with no auth (ex. contact form 7).

dead simple and efficient, but be aware

Disables the WP REST API for visitors not logged into WordPress.

WP Extended Data to REST API vs Disable WP REST API