HTML Checking for Large Sites

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

The target attribute on <a> elements can’t be blank.

This attribute defines the browsing context for links, that is, where should the linked documents be opened. This was used extensively on the now deprecated <frame> element, so you could give the name of the frame to open the document in, but is now more used to force links to open in a separate tab or window using target="_blank". Another option is using a name, so the new browsing context can be referred to on subsequent clicks on links with the same target.

For example, this will force the links to open on a new tab:

<a href="https://example.com" target="_blank">will open a blank tab</a>

Learn more:

• HTML Living Standard: Browsing context names

<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

The accept attribute may be specified to provide browsers with a hint of what file types will be accepted on an <input> element. It expects a comma-separated list of allowed file types. Refer to the list of media types to check the accepted tokens. In this example, the first line is invalid while the second is valid:

<input name='file' type='file' accept='doc, docx, pdf' />

<input name='file' type='file' accept='text/doc, text/docx, application/pdf' />

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

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

<img src="https://example.com/?s=some term" alt="description" />
<img src="https://example.com/?s=some%20term" alt="description" />

The src attribute on an <img> tag is not allowed to contain space characters. You should replace them with “%20“.

The type attribute on <a> elements, when present, gives a hint on the MIME type of the linked resource, for example:

<a href="application/pdf" src="book.pdf">Read our book</a>
<a href="image/jpeg" src="photo.jpeg">See a photo</a>

That is, we’re talking about the type of the linked resource, not the type of the <a> element, as it’s sometimes misunderstood. The following example is invalid because button is not a valid MIME type.

<a href="/order.php" type="button">Submit</a>

Learn more:

• HTML Spec: the type attribute

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

Learn more:

• HTML Spec: the a element

An HTML tag could not be parsed, most probably because of a typo.

An </a> end tag has been found to violate nesting rules. <a> tags can’t include other <a> tags inside. Most probable cause is an unclosed <a> tag, like in this example:

<a href="one.html">Page 1
<a href="two.html">Page 2</a>

A character has been found in the document that is not allowed in the charset encoding being used.

The document has been declared to use a windows-1251 charset but the actual contents seems to be utf-8. You should update the charset to that like in this example:

<meta http-equiv="Content-Type" content="text/html; charset=utf-8">

An <a> tag can’t include other <a> tags inside. Most probable cause is an unclosed <a> tag, like in this example:

<a href="one.html">Page 1
<a href="two.html">Page 2</a>

An <a> element has been found in an invalid place within a <table> element.

For example, the following code would cause this issue:

<table>
  <tr>
    <a href="#">link</a>
  </tr>
</table>

Instead, the <a> element should be inside a <td> element, as a <tr> can’t hold content directly:

<table>
  <tr>
    <td>
      <a href="#">link</a>
    </td>
  </tr>
</table>

Read about Normalization in HTML and CSS.

A <label> tag can’t be used inside an <a> tag. Consider using other tags like <span>.

Links created with the <a> element no longer accept a shape attribute. In order to define image maps, use the <area> element instead.

Learn more:

• MDN: area element