Content before the doctype

Warning severity, in the Content tab

Why it matters

Text, a BOM or stray markup before <!DOCTYPE html> (often PHP output or a template whitespace bug) puts browsers into quirks mode and can push the whole head into the body, where meta tags and the canonical may be ignored.

How to fix it

Make <!DOCTYPE html> the very first bytes of the response; remove output and whitespace before it in the template.

How Crawlune finds it

Crawlune flags Content before the doctype automatically on every crawl and lists the affected URLs under the Content tab, where you can filter, inspect each page and export the list to CSV. The free version crawls up to 550 URLs with every check enabled.