<!doctype>: The DOCTYPE Declaration
Last updated: 2026-10-13
<!doctype>The DOCTYPE Declaration
Declares the document type so the browser knows which HTML version to use. It must be the first line of an HTML document and appear exactly once. Modern pages use <!DOCTYPE html> to switch to standards mode.
| Category | Document Structure |
|---|---|
| Content Model | Before everything, before |
| Allowed Parents | Any element that accepts flow content |
| Content Tag | Self-closing — no closing tag needed |
| Status | Standard |
📝 Syntax
<!DOCTYPE html>▶ Example
Edit the code below and see the live result in the playground:
🌐 Browser Support
| Browser |  Chrome |
 Edge |
 Firefox |
 Safari |
 Opera |
|---|---|---|---|---|---|
| <!doctype> | ✓ v1 | ✓ v12 | ✓ v1 | ✓ v1 | ✓ v1 |
| Supported in all major browsers | |||||
Tip： DOCTYPE is not an HTML tag but a declaration; omitting it triggers quirks mode with inconsistent rendering.
❓ FAQ
QWhat does the DOCTYPE declaration do?
A
<!DOCTYPE html> tells the browser to render the page in standards mode. Without it the browser falls back to quirks mode, where box model and line-height calculations follow decades-old rules and layout develops all kinds of oddities.QIs DOCTYPE case-sensitive? Can it be lowercase?
ACase-insensitive —
<!doctype html> is perfectly valid. Uppercase is convention for visibility. It must be the very first thing in the document: no characters, blank lines, or comments before it. The HTML5 doctype is the shortest of all versions.QWhy were older DOCTYPEs so long?
APre-HTML5 doctypes (HTML4/XHTML) included a DTD address like
-//W3C//DTD HTML 4.01//EN plus a long URL for validators to reference the document type definition. HTML5 cut it to 15 characters and dropped the DTD entirely.🏷️ Related Tags
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