HTML Structure Validator

Check markup for unclosed tags, badly nested elements and misplaced block content, the structural errors browsers silently paper over.

How to use
  1. Paste the HTML you want checked.
  2. Read the reported structural problems.
  3. Fix the nesting and re-check.
Frequently asked questions
What kinds of error does it catch?
Structural ones: unclosed tags, elements closed in the wrong order, and block content inside elements that only accept inline children.
Why does my page look fine if it is invalid?
Because browsers recover aggressively. They guess at what you meant and usually guess right, but two browsers can guess differently, which is where the odd bug comes from.
Does it check accessibility?
No, that is a separate question. Valid markup is a prerequisite for accessible markup, not a substitute for checking labels, roles and contrast.
Is this the same as the W3C validator?
It covers the structural errors that matter in practice and runs locally. The W3C service is more exhaustive and is worth running before a release.
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