The 24 Boolean Attributes of HTML

Post from May 19, 2020 (↻ October 22, 2022), filed under Web Development (feed).

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

1. allowfullscreen
2. async
3. autofocus
4. autoplay
5. checked
6. controls
7. default
8. defer
9. disabled
10. formnovalidate
11. inert
12. ismap
13. itemscope
14. loop
15. multiple
16. muted
17. nomodule
18. novalidate
19. open
20. playsinline
21. readonly
22. required
23. reversed
24. selected

Yes. That’s it.

Update (October 21, 2022)

The list now strictly follows the HTML specification’s attributes overview. That means it doesn’t contain Boolean attributes found on legacy and obsolete elements anymore, like truespeed.

About Me

I’m Jens, and I’m an engineering lead and author. I’ve worked as a technical lead for Google, I’m close to W3C and WHATWG, and I write and review books for O’Reilly. 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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