HTML Guides for HTML language standard

A 405 Method Not Allowed status means the server hosting the linked resource rejected the validator’s request, typically because it doesn’t allow the HTTP HEAD or GET method the validator uses to check the URL.

This is not an error in your HTML code. It’s a server-side issue with the remote resource you’re referencing. The W3C validator tries to fetch external resources (stylesheets, scripts, images, etc.) to verify they exist and are valid. When a remote server blocks those requests, the validator reports this warning.

Common causes include:

• The remote server has strict firewall or bot-protection rules that block requests from the validator.
• The server requires authentication or specific headers to serve the resource.
• The URL points to an API endpoint or resource that only accepts POST requests.

You can safely ignore this warning if the resource loads correctly in a browser. However, if you want to resolve it, consider these options:

• Host the resource yourself instead of relying on the remote server.
• Verify the URL is correct — make sure it points to a publicly accessible file.
• If it’s your own server, ensure it responds to HEAD and GET requests for that resource.

HTML Example

A typical case where this happens:

<!-- A remote stylesheet hosted on a server that blocks validator requests -->

<link rel="stylesheet" href="https://example.com/restricted/styles.css">

Fix: Host the Resource Locally

<!-- Download the file and serve it from your own domain -->

<link rel="stylesheet" href="/css/styles.css">

Self-hosting the resource eliminates the dependency on the remote server and ensures the validator can access it.