HTML Doctype
Checks for <!DOCTYPE html> at the start of the document.
What this check measures
We verify the response starts with `<!DOCTYPE html>` (case-insensitive). Missing doctype triggers quirks mode in browsers — unpredictable rendering.
Why it matters
Quirks mode disables modern CSS, triggers wrong box model calculations, breaks layouts. Every modern framework ships doctype — missing one is usually a sign of hand-written template problems.
How our audit detects it
Read first 100 bytes of HTML response, check for doctype declaration.
Typical findings
- error_outlineHTML starts with `<html>` directly — quirks mode.
- error_outlineOld doctype (HTML 4 strict) — legacy code.
How to fix
Ensure every HTML response starts with `<!DOCTYPE html>` (HTML5). Frameworks do this automatically; manual templates need it explicit.
Frequently asked questions
Any doctype or HTML5?expand_more
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