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Doctype Checker
Free doctype checker — verify your HTML document type declaration is valid and correctly placed. Ensure proper rendering mode across all browsers.
Frequently Asked Questions
Why is the DOCTYPE declaration important?
The DOCTYPE declaration tells browsers which HTML version to use for rendering. Without it, browsers enter "quirks mode" which can cause inconsistent layouts and CSS behavior across browsers.
What is the correct HTML5 DOCTYPE?
The HTML5 DOCTYPE is simply <!DOCTYPE html>. It must be the very first line of your HTML file, before the <html> tag. It's case-insensitive but conventionally uppercase.
Does DOCTYPE affect SEO?
Indirectly, yes. A missing or incorrect DOCTYPE can cause rendering issues that affect user experience and Core Web Vitals scores, both of which influence search rankings.
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