HTML Guide
<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>Related W3C validator issues
The href attribute of an <a> element contains an invalid character, that should be properly encoded as a URI percent-encoded character.
The href attribute of the a element contains an invalid backslash character, which is not permitted in URLs.
According to the WHATWG HTML living standard, the href attribute must contain a valid URL. URLs use forward slashes (/) for path separators, and backslashes are not allowed as they can cause browsers and validators to misinterpret the address. Backslashes often arise when file paths are copied from Windows environments.
Correct Usage:
- Always use forward slashes / in your URLs.
- Remove any backslashes from href values.
Example of incorrect usage:
<a href="images\picture.jpg">View Picture</a>Corrected example:
<a href="images/picture.jpg">View Picture</a>The W3C HTML Validator issue you encountered indicates that the URL provided in the href attribute of an anchor (<a>) element is not formatted correctly.
How to Fix the Issue
- Check the Protocol: For a valid URL, make sure that after https: there are two slashes (//).
- Update the URL: Correct the URL format to include the missing slash.
Example of Incorrect HTML
Here is an example of the code that would trigger the validation error:
<a href="https:/example.comf">Example</a>Corrected HTML
Here’s how the corrected code should look:
<a href="https://example.com">Example</a>Summary
Make sure that all URLs within href attributes are correctly formatted with both slashes following the protocol (https:// or http://).
An href attribute on an a element contains an invalid URL that has space characters in the domain.
The domain in a URL cannot contain space characters, for example the following are invalid:
<a href="http://my domain.com">link</a>
<a href="http://my%20domain.com">link</a>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>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.
Empty type attributes are invalid on the <a> element; you must either remove the type attribute or provide a valid MIME type value.
The type attribute on an <a> (anchor) element specifies the MIME type of the linked resource. According to the WHATWG HTML specification and W3C validator, the value of the type attribute cannot be an empty string. It should be a valid MIME type, such as application/pdf or text/html. If you do not know the MIME type or it’s not relevant, you should omit the attribute.
Incorrect HTML example (causes validation error):
<a href="document.pdf" type="">Download PDF</a>Correct HTML example (remove the invalid attribute):
<a href="document.pdf">Download PDF</a>Correct HTML example (provide a valid MIME type):
<a href="document.pdf" type="application/pdf">Download PDF</a>If the type is unknown or unnecessary, leaving it out is preferred to using an empty value.
The href attribute on an a tag expects a valid URL, but only http(s):// was found.
Hash (#) characters can be used in an href attribute to link to a specific part of a document.
For example, if we have this page with several sections, each of them marked with an ID:
<h1>Frequently Asked Questions</h1>
<h2 id="pricing">Pricing</h2>
<p>All about pricing...</p>
<h2 id="terms">Terms</h2>
<p>You can find our terms at...</p>
<h2 id="guarantee">Guarantee</h2>
<p>We offer a guarantee...</p>You can link to a specific part of that document, for example if this page URL is /faqs and you want to link to the Guarantee section you could use:
<a href="/faqs#guarantee">Guarantee</a>Or, if you’re linking from inside the same document, for example in a table of contents, you could just use:
<a href="#guarantee">Guarantee</a>As there can only be one fragment in an URL, the # character should only be used once. The following would be an invalid href:
<a href="/faqs#guarantee#pricing">Bad</a>If needed, the # could be encoded as %23.
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#some term">invalid</a>
<a href="https://example.com#some%20term">valid</a>