HTML Validator
Run a lightweight tag-pair check to spot possible nesting mistakes in HTML. This is a quick editing aid using heuristic rules, rather than a complete conformance checker for the HTML standard.
- Runs in your browser
- Nothing is uploaded
- No signup; device limits apply
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How to use this tool
Paste an HTML fragment and compare reported problems with the source. A regular-expression and stack approach needs extra caution around script strings and legally omitted end tags.
Results and examples
An input such as <div><span>text</div> is worth checking for an unmatched span. Browser error recovery and optional syntax mean a heuristic result can still include false positives or omissions.
Limitations
- The check does not implement every WHATWG parsing rule or element constraint.
- A pass does not certify accessibility, security or standards conformance.
Fields
| Field | Guidance and constraints |
|---|---|
| HTML | Check the unit and format displayed beside this field. |
| Details | Check the unit and format displayed beside this field. |
Data handling
Processing stays in the current browser tab; the site does not upload tool input for the calculation itself.
Sources
Frequently asked questions
What kind of mistake can it reveal?
An input such as text is worth checking for an unmatched span. Browser error recovery and optional syntax mean a heuristic result can still include false positives or omissions.
Does a pass mean conforming HTML?
The check does not implement every WHATWG parsing rule or element constraint. A pass does not certify accessibility, security or standards conformance.
