HTML Comments

1) Basic Syntax

<!-- This is a comment -->
<p>Visible content</p>

Rendered output shows only: Visible content

2) Comment Out Code (Disable Temporarily)

<!-- <h2>This heading is hidden</h2> -->
<p>This paragraph is visible</p>

3) Don’t Split Tags with Comments

<!-- Correct -->
<a href="page.html">Read more</a>

<!-- Avoid putting a comment between tag name and > or attributes -->
<!-- Wrong: <a <!-- note --> href="page.html">... -->

4) Multi-line Notes / TODOs

<!--
 TODO: Replace placeholder image
 NOTE: Keep this section short
-->

5) Conditional Comments (Legacy IE Only)

<!--[if lt IE 9]>
  <p>You are using an old version of Internet Explorer.</p>
<![endif]-->

These worked only in very old Internet Explorer versions. Modern browsers ignore them.

6) Comments are Not Secure

<!-- API key goes here (DON'T DO THIS) -->

Never put secrets in comments. Anyone can view source and read them.