Are HTML tags case sensitive?
No. HTML tags are not case sensitive. You can write all HTML tags in lowercase or uppercase and they will be correctly rendered on a browser. This means that
<h1>lowercase</h1> and <H1>UPPERCASE</H1> will work on any browser.
Does case matter in HTML?
It does not matter which case you use. HTML can be uppercase, lowercase, mixed case or lowercase. However there are a few exceptions.
WHATWG a body that works on improving the current version of HTML states:
’ Many strings in the HTML syntax (e.g. the names of elements and their attributes) are case-insensitive, but only for ASCII upper alphas and ASCII lower alphas. For convenience, in this section this is just referred to as “case-insensitive”.’
Some of the places where case matters is some HTML entities that are used to display non-keyboard characters. e.g.
To display uppercase Ñ you need to use the entity with an uppercase:
Ñ and a lowercase ñ you use lowercase entity
HTML Case recommendation
It is generally recommended that you use lowercase in HTML. I think its also easier to write HTML in lowercase as long as you are typing your sentences in lowercase.
If you click on inspect on a page written in uppercase HTML code, you will find that the browser seems to have converted all the tags to lowercase.