`description.single`

Default: error
Plugin: description

A page has only one description tag.

Why: With more than one description, search engines pick one, and may not pick the one you want.

When off: pages with many descriptions pass.

<!-- ✗ Fails -->
<meta name="description" content="Our bakery." />
<meta name="description" content="Fresh bread every morning." />

<!-- ✓ Passes -->
<meta name="description" content="Fresh bread every morning." />

References

HTML spec: The description metadata name: A document must not have more than one description meta tag.