Bad value X for attribute “href” on element “a”: Illegal character in path segment. “"” is not allowed.

The href value on the <a> element contains a literal " character, which is not allowed in a URL path.

The quotes around an attribute value are HTML syntax, not part of the URL. A " inside the value is different: written as ", or typed inside a single-quoted attribute such as href='"/brochure.pdf"', it becomes a character of the URL itself. The URL standard does not allow a raw " in a path, so the validator rejects the whole value. Browsers still follow the link, but they send the quote as %22 and request a path that usually does not exist.

The stray quote rarely comes from someone typing it. More often the code that writes the link adds it. A template that JSON-encodes the URL before printing it, for example with JSON.stringify(url), wraps the address in an extra pair of quotes. A CMS that stores link settings as JSON, like {"url":"/brochure.pdf","target":"_blank"}, can print the wrong piece of that string, so href ends up holding a fragment such as "url":"/brochure.pdf" or the tail of the object instead of the address. Fix the template so it outputs the plain URL. If a file name really contains a double quote, write it as %22 in the path.

Invalid example

<a href="&quot;/brochure.pdf&quot;">Download the brochure</a>

Valid example

<a href="/brochure.pdf">Download the brochure</a>

Learn more:

MDN Reference

MDN Web Docs: The Anchor element

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MDN Reference

MDN Web Docs: Percent-encoding

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WHATWG Spec

WHATWG URL Living Standard

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