Top 10
HTML Issues

Void elements, like area, base, br, col, embed, hr, img, input, link, meta, source, track, and wbr are self-closing and don’t need a trailing slash /, which should be avoided as that can interfere with unquoted attribute values.

The default type for <script> tags is JavaScript, so you don’t need to include the type for JS resources.

The document could not be properly parsed due to malformed characters. Check the document encoding.

Element IDs in an HTML document must be unique. The HTML validator is indicating the first occurrence of an ID that is repeated. Check the details for that issue to see web pages affected, and the elements within them, to fix that ID repetition.

The id attribute is used to identify a single element within a document, and is required to be unique. Check the document for repeated IDs.

Attributes in HTML elements need to be separated by space.

An invalid attribute has been found on an element. Check the affected tag to ensure attributes are well-formed, and if they are you can consider using custom data attributes.

The element X is not allowed as a child element of Y. For example, a <ul> element cannot have a <div> child element.

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

Malformed comment syntax has been found, check out the affected comment.

HTML comments are helpful to leave notes about the code right next to it. To create a comment, it must start with <!-- and end with -->.