The 24 Boolean Attributes of HTML
Post from May 19, 2020 (↻ May 25, 2022), filed under Web Development.
There are Boolean attributes in HTML and, unless I err somewhere, there are two dozen of them. Here’s a quick rundown of what makes for a Boolean attribute, and what Boolean attributes there are in current HTML.
What is a Boolean at all? Citing the The Web Development Glossary, a Boolean is “a data type that has one of two possible values (usually denoted true and false).”
What is a Boolean attribute? A Boolean attribute is an attribute that can only be true or false.
How does a Boolean attribute work? According to the HTML specification:
The presence of a boolean attribute on an element represents the “true” value, and the absence of the attribute represents the “false” value.
Yet note:
The values “true” and “false” are not allowed on boolean attributes. To represent a false value, the attribute has to be omitted altogether.
So, what Boolean attributes are there?
The Boolean Attributes
allowfullscreen
async
autofocus
autoplay
checked
controls
default
defer
disabled
formnovalidate
ismap
itemscope
loop
multiple
muted
nomodule
novalidate
open
playsinline
readonly
required
reversed
selected
truespeed
Yes. That’s it.
About Me

I’m Jens Oliver Meiert, and I’m an engineering lead and author. I’ve worked as a technical lead for Google, I’m close to the W3C and the WHATWG, and I write and review books for O’Reilly. Other than that, I love trying things, sometimes including philosophy, art, and adventure. Here on meiert.com I share some of my views and experiences.
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Perhaps my most comprehensive book: The Web Development Glossary (2020). With explanations and definitions for literally thousands of terms from Web Development and related fields, building on Wikipedia as well as the MDN Web Docs. Available at Apple Books, Kobo, Google Play Books, and Leanpub.