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Tools / Validators & Inspectors

HTML structural checker

Check explicit markup nesting and selected structural errors.

Input

0 UTF-16 code units

Optional local draft

Saving stores a plaintext draft in this browser on this device. Do not save secrets or use this on a shared device. Nothing is saved or loaded automatically. Reset does not delete a saved draft; use Delete local draft.

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Import a local text file

Output

Work through the task
Check explicit tag nesting and selected markup errors.
  1. Write the closing tags explicitly, then choose Check HTML structure.
  2. Read the first structural diagnostic and its location. Optional end tags and full browser error recovery are outside this check.
  3. Review the result before copying or downloading. Editing an input invalidates the previous result; keep an original if the transformation matters.
Example to check
<p><b>x</p> is rejected because the closing tags do not match the explicit nesting.
Limits and output behavior
Maximum 100,000 input characters, 10,000 markup tokens and 40 nesting levels. Structural checking is a bounded explicit-tag subset, not full HTML5 validation or browser recovery. Static Pug excludes code, includes, interpolation, mixins and template control flow.
Troubleshooting
Write closing tags explicitly and correct the first mismatched nesting location. Browser recovery and optional-end-tag conventions are outside this checker.
Questions
Can a browser display HTML that this checker rejects?
Yes. Browsers perform extensive HTML recovery. This bounded checker verifies its explicit-tag subset rather than implementing full HTML5 validation.
Input and privacy
Processing runs in this browser. Inputs are not saved automatically. An explicitly chosen local draft, where offered, is plaintext storage on this device. Downloaded files, clipboard contents and browser extensions have separate retention behavior.