HTML Guide
The href attribute on an <a> link contains an invalid character. 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>Learn more:
Related W3C validator issues
Empty href attributes like href or href="" are invalid in HTML and can cause unpredictable behavior.
According to the HTML specification, the href attribute in elements such as the a and link tags must contain a valid URL or fragment reference. An empty or omitted href results in the attribute being ignored or possibly causing compatibility problems, especially in older browsers. If you intend the link to do nothing, use href="#" and prevent the default action with JavaScript, or avoid making it a link if no action is necessary.
Valid HTML for a regular link:
<a href="https://example.com">Visit Example</a>Valid usage for a link that does nothing:
<a href="#" onclick="return false;">Do nothing</a>If the element should not be clickable, use a different tag such as span or button:
<span>Not a link</span>or
<button type="button">Not a link</button>Avoid writing:
<a href>Invalid link</a>or
<a href="">Invalid link</a>as these will produce the validation warning you saw.
The maxlength attribute can be used on an input element to define a client-side validation for the maximum length allowed on an input without resorting to JavaScript.
This attribute is only allowed on elements of type email, password, search, tel, text, or url.
The minlength attribute can be used on an input element to define a client-side validation for the maximum length allowed on an input without resorting to JavaScript.
This attribute is only allowed on elements of type email, password, search, tel, text, or url.
The minlength attribute defines the minimum number of characters (as UTF-16 code units) the user can enter into an <input> or <textarea>. This must be an integer value 0 or higher. If no minlength is specified, or an invalid value is specified, the input has no minimum length. This value must be less than or equal to the value of maxlength, otherwise the value will never be valid, as it is impossible to meet both criteria.
Here’s an example:
<label for="name">Enter your name (max 25 characters)</label>
<input type="text" minlength="25" id="name">The pattern attribute is only allowed on input whose type is email, password, search, tel, text or url. Check the type used, and consider changing to one of the allowed types to enable pattern client-side validation.
The pattern attribute is a handy way of adding client-side validation on HTML forms without resorting to JavaScript. Check out this article to learn more about Input Pattern.
The boolean required attribute can only be used with certain types of inputs. Check the input type is one of the allowed.
The required attribute, if present, indicates that the user must specify a value for the input before the owning form can be submitted.
An <a> element has been found with an invalid href attribute, containing more than one # adjacent character.
The # is used to separate the fragment part of an URI (typically used to indicate a section within a document). For example, this is a valid link to a URI containing a fragment:
<a href="https://example.com/faqs#pricing">pricing</a>The next example is invalid because it contains two adjacent # characters, so that the fragment part would be #pricing instead of pricing:
<a href="https://example.com/faqs##pricing">pricing</a>The href attribute of an <a> element contains an invalid character, that should be properly encoded as a URI percent-encoded character.
An illegal character has been found for the “href” attribute on the “link” element.
To fix this issue, find the “link” element in question and make sure that the “href” attribute contains a valid URL without any illegal characters.
Here’s some example HTML code of a link element:
<!DOCTYPE html>
<html>
<head>
<title>My Webpage</title>
<link rel="stylesheet" href="styles/main.css">
</head>
<body>
<h1>Welcome to my webpage!</h1>
<p>Here is some content...</p>
</body>
</html>In the above example, the link element has a valid href attribute value of styles/main.css. Make sure that your href attribute values don’t contain any illegal characters.
The href attribute on the link element must not be empty.
The href attribute on an a tag expects a valid URL, but only http(s):// was found.