HTML Guide
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:
Related W3C validator issues
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">HTTP status code 202 means the server has accepted the request but has not completed processing it, so the validator cannot retrieve the resource.
The W3C HTML Validator needs to retrieve external resources (like linked CSS or JS files, images, or even your webpage itself) and expects a successful 200 OK HTTP status code. If it gets a 202 Accepted instead, the resource is not fully available for validation, which prevents it from fetching and checking the content.
Causes:
- Your server is responding with a 202 Accepted and processing in the background instead of serving the full content immediately.
- You might be testing a URL that triggers background processing, a queue, or is incomplete.
- If your resource is an API or dynamic endpoint, make sure to provide a static, direct file with a 200 OK response for validation.
How to fix:
- Configure your server to respond with 200 OK and immediately provide the requested content for HTML documents or resources.
- Avoid validating URLs that return 202 Accepted. Only validate URLs serving complete resources.
The “HTTP resource not retrievable” error with an HTTP status code of 404 indicates that the W3C Validator could not find a specific web page by its URL. This error occurs when the URL provided for a page is incorrect, or the page no longer exists at the given address.
The “HTTP resource not retrievable” error with an HTTP status code of 503 indicates that the W3C Validator could not access a web page referenced in your HTML. This error occurs when the remote server hosting the page is temporarily unavailable or overloaded.
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.
A stray start tag <html> has been found in the document. As this tag defines the start of the whole HTML document, it should appear only once.
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>