How to add external CSS and JS Url in Magento2?

You can add External third-party JS,CSS, and fonts URL using Magento 2 by XML at below way, All the Url will be staying in  <head> tag. Pass Second attribute as  src_type=”url”

For set third-party JS link,

<head>
	<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.4/js/bootstrap.min.js" src_type="url" />
</head>

For set third-party CSS link,

<head>
	<css src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.4/css/bootstrap-theme.min.css" src_type="url" />
</head>

For set font link,

<head>
	<link src="http://fonts.googleapis.com/css?family=Montserrat" src_type="url" />
</head>

For Remove link from the page,  If you want to remove specific JS or CSS from the specific page you can use <remove> tag under the <head> to remove from a specific page.

<head>
    <remove src="ttps://maxcdn.bootstrapcdn.com/bootstrap/3.3.4/js/bootstrap.min.js" />
    <remove src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.4/css/bootstrap-theme.min.css" />
    <remove src="http://fonts.googleapis.com/css?family=Montserrat" />
</head>