When are quotes required for the values of html attributes?
Jun 27, 2025 am 01:58 AMIn HTML, attribute values ??require quotes in most cases, but sometimes they can be omitted. Quotes must be used including when the attribute value contains spaces, special characters or multiple words, such as: src="my photo.jpg", , class="my-class active", otherwise it may lead to parsing errors. Quotes can be omitted when the attribute value is a simple word or number and does not contain spaces or special characters, such as: required, id=myDiv, class=myClass. Reasons for always using quotes include better compatibility, strong readability, avoiding syntax errors and smoother teamwork, such as the use of href="#" and onclick="alert('hi')" will be clearer and more standardized.
In HTML, when do attribute values ??need to be quoted? Simply put: it is required in most cases, but sometimes it can be omitted. However, for the sake of clearness and compatibility of the code, it is recommended to always use quotes.

Quotes must be used
If your property value contains spaces, special characters, or multiple words, it must be enclosed in quotes. for example:

-
<img src="/static/imghw/default1.png" data-src="https://img.php.cn/upload/article/000/000/000/175096073750699.jpeg" class="lazy" alt="When are quotes required for the values of html attributes?" >
-
<a href="https://example.com?query=1&name=test"></a>
If you don't put quotes, the browser may misunderstand what you mean and only read the content before the first space, causing the link to be invalid or the image to be unable to load.
In addition, although the HTML5 specification allows for some cases without quotes, it is not possible to not use quotes when multiple class names such as class="my-class active"
.

Quotes can be omitted
If the property value is a simple word or number and does not contain spaces, special characters (such as =, , `, ", ', (), etc.), then you can choose not to include quotes. For example:
-
<input required>
-
<div id="myDiv"> <li> <code><span class="myClass"></span>
- Better compatibility : Older browsers support for quotation-free attributes is unstable.
- Strong readability : you can see the starting and ending positions of the attribute value at a glance.
- Avoid syntax errors : Once there are equal signs or special symbols in the property value, there will be problems without quotation marks.
- Teamwork is smoother : Unify style and reduce understanding costs.
This writing method is legal in HTML5, but it is prone to errors in actual development, especially when multiple people collaborate, others may accidentally modify the format, resulting in parsing errors.
Why is it recommended to always use quotes?
Although quotes can sometimes be omitted, this risk outweighs convenience. Here are a few reasons to always put quotes:
For example, the following line of code:
<a href=# onclick=alert('hi')>
Although it can run, the structure is chaotic. Change to:
<a href="#" onclick="alert('hi')">
It's much clearer.
Basically that's it. Whether to add quotation marks to HTML attribute values ??can sometimes be processed flexibly, but developing the habit of adding quotation marks will make you less trapped.
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