HTML Guides for invalid host

When you set href="http://", the browser and the W3C validator attempt to parse this as an absolute URL. According to the URL Standard, a URL with the http or https scheme must include a non-empty host component. The string http:// has the scheme but nothing after the ://, which makes the host empty and the URL invalid.

This issue typically arises when a URL is dynamically generated but the variable or value for the domain is missing, or when a developer uses http:// as a temporary placeholder during development and forgets to replace it.

Why this matters

• Broken navigation: Clicking a link with href="http://" leads to unpredictable behavior. Some browsers may navigate to an error page, while others may interpret it differently.
• Accessibility: Screen readers announce links to users, including their destinations. An invalid URL creates a confusing experience for assistive technology users who expect the link to go somewhere meaningful.
• Standards compliance: The HTML specification requires that href values be valid URLs. An empty host violates the URL parsing rules, causing the W3C validator to flag it as an error.
• SEO: Search engine crawlers may treat invalid URLs as errors, potentially affecting how your site is indexed.

Examples

❌ Invalid: empty host in URL

<a href="http://">Visit our website</a>

This triggers the error because http:// has no host component.

❌ Invalid: same issue with HTTPS

<a href="https://">Secure link</a>

The https scheme also requires a valid host, so this produces the same error.

✅ Fixed: provide a complete URL

<a href="https://example.com">Visit our website</a>

✅ Fixed: use a fragment placeholder if the URL is unknown

If you need a placeholder link during development, use # instead of an incomplete URL:

<a href="#">Visit our website</a>

✅ Fixed: use a relative URL when linking within the same site

<a href="/about">About us</a>

Handling dynamic URLs

If the href value comes from a template or CMS, make sure the variable outputs a complete URL. For example, if a template produces an empty string, you might end up with:

<!-- If {{ site_url }} is empty, this becomes href="http://" -->

<a href="http://{{ site_url }}">Home</a>

Ensure that the variable always resolves to a valid host, or add a fallback so the link is omitted or replaced with a safe default when the value is missing.