Does it give the same results as the official W3C validator?

No. This tool is a practical checker focused on common issues — mismatched tags, duplicate ids, missing alt, etc. — and isn't a full HTML5 spec validation.

What does it flag as a warning?

It warns about a missing DOCTYPE, deprecated tags (center, font, etc.), a missing lang attribute, and missing alt on img elements.

Is the code I enter sent to a server?

No. It's checked entirely in your browser.

🔍 HTML5 Validator

Checks for common HTML issues like mismatched tags, duplicate ids, and missing alt attributes.

⚠️ Practical checker — not a full spec validation at the level of the official W3C validator

HTML Code

How to use

Enter your HTML code.
Click "Check".
Issues like mismatched tags, duplicate ids, and missing alt are listed.

🎯 Use Cases

Catch mismatched tags after finishing markup
Find duplicate id attributes
Check whether image alt attributes are missing

Example

Input

<!DOCTYPE html>
<html>
<img src="logo.png">
<p id="main">A</p>
<p id="main">B</p>
</html>

Output

❌ 5번째 줄: id="main" 가 4번째 줄과 중복됩니다
⚠️ 2번째 줄: <html> 에 lang 속성이 없습니다
⚠️ 3번째 줄: <img> 에 alt 속성이 없습니다

The duplicate id="main" is reported as an error (❌), while the missing lang on <html> and the missing alt on <img> are reported as warnings (⚠️), each with the line number where the issue occurs. Messages are shown in Korean.

FAQ

Does it give the same results as the official W3C validator?: No. This tool is a practical checker focused on common issues — mismatched tags, duplicate ids, missing alt, etc. — and isn't a full HTML5 spec validation.
What does it flag as a warning?: It warns about a missing DOCTYPE, deprecated tags (center, font, etc.), a missing lang attribute, and missing alt on img elements.
Is the code I enter sent to a server?: No. It's checked entirely in your browser.