HTML Checking for Large Sites

The href attribute on the link element must not be empty.

<a> tags can be used to link to an email address using the mailto protocol in the href attribute. Ensure that there is no space in the email address.

<a href="mailto: liza@example.com">This is wrong as it contains an space</a>

<a href="mailto:liza@example.com">This is OK</a>

The href attribute on an <a> link contains a space character, which is not allowed. If you’re trying to link to a phone URL, review the href attribute to remove unallowed characters, as in this example:

<!-- Invalid as it contains a space character -->
<a href="tel: +123456789">call me</a>

<!-- Valid -->
<a href="tel:+123456789">call me</a>

Source:

• IETF: tel URI for Telephone Numbers

Space characters are not allowed in href attributes. Instead, they should be converted to %20. In this example, the first line is invalid and the second is valid:

<a href="https://example.com/?s=some term">invalid</a>
<a href="https://example.com/?s=some%20term">valid</a>

The href attribute on an element <a> contains a | character, also known as vertical pipe.

This character is not allowed and should be replaced by its encoded alternative %7C .

The href attribute on an <a> tag contains an space, which is not allowed. Consider replacing space characters with “%20”.

The at symbol (@) should be percent-encoded as %40 in order to include it at an href attribute.

The <a> element requires either a href attribute, or a role attribute.

Learn more:

• HTML Spec: the a element