HTML Validation

HTTP resource not retrievable. The HTTP status from the remote server was: 403.

html
403

About This HTML Issue

The validator is blocked from accessing an external resource such as a stylesheet, script, or image due to a 403 (Forbidden) HTTP status.

This means that the HTML references a resource (often in a link, script, img, or iframe element) at a URL that is denying access—possibly due to server permissions, IP restrictions, or hotlink protection. The validator needs to retrieve these resources to check them, so HTTP 403 errors will prevent validation of external resources.

Learn more:

→ MDN: 403 Forbidden

Last reviewed: May 08, 2025

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Related W3C Validator Issues (9)

Attribute “isolang” not allowed on element “html” at this point.

Instead of using the isolang attribute to define the language of the document, you can use lang with an ISO 639-1 two character code.

For example, for Portuguese:

<html lang="pt">

Bad value X for attribute “multiple” on element “input”.

Invalid value used for the multiple attribute on an input element.

The multiple attribute is a boolean attribute for certain input types (e.g., email, file). Boolean attributes must appear without a value (or with the same name as value in legacy cases), and they only work on specific types. Valid usage: <input type="email" multiple> or <input type="file" multiple>. Invalid usage includes multiple="1", multiple="true", or using multiple on unsupported types like text or number. The email type allows comma-separated addresses when multiple is present; the file type allows selecting more than one file.

HTML Examples

Example that reproduces the error

<!DOCTYPE html>
<html lang="en">
<head>
  <title>Invalid multiple</title>
</head>
<body>
<!-- Invalid: value on boolean attribute, and wrong type -->

  <input type="text" name="tags" multiple="1">
</body>
</html>

Corrected example

<!DOCTYPE html>
<html lang="en">
<head>
  <title>Valid multiple</title>
</head>
<body>
<!-- Valid: boolean attribute without a value on supported types -->

  <input type="email" name="recipients" multiple placeholder="name@example.com, other@example.com">

  <input type="file" name="attachments" multiple>
</body>
</html>

HTTP resource not retrievable. The HTTP status from the remote server was: 202.

html
202

HTTP resource not retrievable. The HTTP status from the remote server was: 404.

HTTP resource not retrievable. The HTTP status from the remote server was: 429.

HTTP resource not retrievable. The HTTP status from the remote server was: 503.

html
503

Quirky doctype. Expected “<!DOCTYPE html>”.

doctype
html

The <!DOCTYPE html public "-//W3C//DTD HTML 4.0 Transitional//EN"> doctype triggers quirks mode in modern browsers and is not compliant with HTML5 standards.

The HTML5 specification requires the use of a simple doctype declaration, which ensures standards mode rendering. The correct doctype is <!DOCTYPE html>, which must appear at the very top of every HTML5 document. Legacy doctypes like HTML 4.0 Transitional are obsolete for modern web development and can cause inconsistent browser behavior.

Example of correct usage:

<!DOCTYPE html>
<html lang="en">
  <head>
    <title>Valid HTML5 Doctype Example</title>
  </head>
  <body>
    <p>Your content here.</p>
  </body>
</html>

Replace any legacy or malformed doctype with the above declaration to conform to current HTML standards.

Stray start tag “html”.

The “version” attribute on the “html” element is obsolete. You can safely omit it.

In HTML5, there’s no need to specify the version attribute - it is now obsolete. Here’s an example minimal HTML document to start with:

<!DOCTYPE html>
<html lang="en">
  <head>
    <title>Test</title>
  </head>
  <body>
    <p></p>
  </body>
</html>

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