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HTML Validator
A fast check for the structural mistakes that break pages most often: a missing doctype, forgotten html/head/title/body elements, unclosed or mismatched tags, and duplicate id attributes.
How to use the HTML Validator
- Paste your HTML into the input box.
- Press Validate.
- Errors (which break the structure) and warnings (worth fixing) are listed separately.
- Work through the list, fix each item, and validate again.
About this tool
Honesty first: this is a common-error check, not official W3C validation, and it does not check every rule in the HTML specification. What it does catch is the short list of structural problems behind most broken layouts — tags left open, tags closed in the wrong order, the same id used twice, and required document elements that never made it into the file. For a full specification audit, use the W3C's own validator as well.