RAWHTML is a lightweight tool for validating HTML code with the use of the open API from html5.validator.nu.
Clone or download the project and place the dist folder in the root directory. Then import the script in all the HTML files by writing <script src="/dist/raw.min.js"></script>.
Note that this tool requires you to run a local web server in order to work.
Simply copy the following code and paste it in your HEAD tag:
<script src="https://cdn.jsdelivr.net/gh/johan3040/rawHTML/dist/raw.min.js"></script>
<link rel="stylesheet" href="https://cdn.jsdelivr.net/gh/johan3040/rawHTML/dist/raw.min.css">