Are HTML5 Tags Case Sensitive?

Best practices for writing HTML5 elements

New web designers may wonder whether HTML tags are case sensitive. While the short answer is that HTML tags aren't case sensitive, there are important rules and best practices to consider when writing HTML markup.

HTML code for building a web form
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Throwing It Back to XHTML

Before HTML5 came onto the scene, web professionals used a different markup language called XHTML to build web pages.

When you write XHTML, you must write all standard tags in lowercase because XHTML is case sensitive. This means that the XHTML tag is a different tag than in HTML. You had to be very specific about how you coded an XHTML web page, using only lowercase characters.

This strict rule was a benefit to many new web developers. Instead of writing markup with a mix of lowercase and uppercase, they knew they must follow an exact format.

For anyone who got involved in web design when XHTML was popular, the idea that markup could be a mix of uppercase and lowercase would seem strange.

HTML5 Gets Loose

Prior versions of HTML weren't case-sensitive, and HTML5 followed along with this tradition, moving away from XHTML's stricter formatting requirements.

Since HTML5 isn't case-sensitive, it means that all XHTML tags are the same tag in HTML5.

The idea behind HTML5 eschewing case-sensitivity was to make it easier for new web professionals to learn the language. However, many experienced professionals disagree, arguing that giving web design students a definitive set of rules, such as "always write HTML as lowercase," is more straightforward. Too much rule flexibility may confuse new web design students.

Lowercase Is an HTML5 Convention

While it's not a strict rule, writing HTML5 tags in all lowercase is a widely used convention. This is partly because many seasoned web developers, who lived through the days of strict XHTML, carried over those best practices to HTML5 and beyond. While a mix of uppercase and lowercase letters is valid, many web designers prefer to stick to all lowercase letters.

As newer web developers examine more experienced professionals' code, they'll notice the all-lowercase markup and will likely continue this practice.

Best Practices for Letter Casing

Many experts agree that using lowercase letters for HTML code, as well as for filenames, is helpful. For example, certain servers are case-sensitive when it comes to filenames (for example, logo.jpg is seen differently than logo.JPG). So, if you have a workflow where you always use lowercase letters, you never need to question whether the casing causes a problem, such as missing images.

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Kyrnin, Jennifer. "Are HTML5 Tags Case Sensitive?" ThoughtCo, May. 14, 2021, thoughtco.com/html5-tags-case-sensitive-3467997. Kyrnin, Jennifer. (2021, May 14). Are HTML5 Tags Case Sensitive? Retrieved from https://www.thoughtco.com/html5-tags-case-sensitive-3467997 Kyrnin, Jennifer. "Are HTML5 Tags Case Sensitive?" ThoughtCo. https://www.thoughtco.com/html5-tags-case-sensitive-3467997 (accessed July 25, 2021).