Max Cutler

Uses PHP’s output buffering to buffer XML-RPC responses and strip superfluous whitespace.
Plugins, themes, and any other files executed during the WordPress load process can unintentionally emit whitespace, 
such as by including a newline character after an explicit closing “?>” PHP tag instead of letting PHP auto-close the 
file.

XML-RPC De-whitespacer

Removes leading and trailing whitespace from XML-RPC responses that can break some XML-RPC clients.

DeveloperWil

Completely disables the XML-RPC API which was introduced in WordPress 3.5 and above which lets remote clients post, upload and edit content.
Notes: 
If you are using the WordPress smart phone app or the Jetpack plugin, please note that they need this service enabled.
If you activate this plugin your WordPress phone app will not be able to connect to your site and Jetpack will not be able to connect to wordpress.com where site visitor data (and other stuff) is stored.
Other plugins and services that use the XML-RPC API will also not function properly.
<h4>Plugin Page</h4>
<a href="https://zeropointdevelopment.com/wordpress-plugins/deactivate-xml-rpc-service-wordpress-plugin/" title="Deactivate XML-RPC Service WordPress Plugin" rel="nofollow ugc">Deactivate XML-RPC</a>

Deactivate XML-RPC Service

Disables the XMP-RPC API service introduced in WordPress 3.5 and above.

XML-RPC De-whitespacer vs Deactivate XML-RPC Service