HTML heading outline checker
Inspect pasted markup for skipped levels and empty headings.
How to use HTML heading outline checker
The HTML heading outline checker parses pasted markup and lists every h1 to h6 heading in document order with its level and text. It flags empty headings and skipped levels, such as an h3 directly after an h1, and marks the rest OK. It checks static markup up to 200,000 characters; script-inserted or CSS-hidden headings are not evaluated.
- Paste the source into the input editor, or load the built-in example.
- Check the source format before running the operation.
- Run html heading outline checker, review the output, then use the available copy or download controls.
What this tool supports
Inspect pasted markup for skipped levels and empty headings.
Limits and processing
Images use the existing 32-megapixel canvas bound. Up to 100 source images are allowed where supported. Pasted HTML is bounded to 200,000 characters; Mermaid diagrams to 20,000 characters and 300 lines. SVG and PNG generation require a browser.
Example source
<h1>Guide</h1><h3>Getting started</h3><h2></h2>
Frequently asked questions
Is it an error to skip heading levels?
The checker flags any heading more than one level deeper than the one before it, such as h2 followed by h4, so you can review the structure. Moving back up, for example from h4 to h2, is not flagged.
Can I check the headings of a live web page?
Paste the page's HTML; the tool does not fetch URLs. Because it reads static markup only, headings inserted by JavaScript after load will not appear unless you copy the rendered HTML from your browser's developer tools.
Does it detect ARIA headings like role=heading?
No. Only h1 to h6 elements are collected, and role and aria-level attributes are ignored. A heading containing only an image or whitespace is reported as empty, because its text content is blank.
Where is my input processed?
This operation processes its source in your browser. Copy and download are explicit actions; source input is not saved in an account or history.
What are the input limits?
Images use the existing 32-megapixel canvas bound. Up to 100 source images are allowed where supported. Pasted HTML is bounded to 200,000 characters; Mermaid diagrams to 20,000 characters and 300 lines. SVG and PNG generation require a browser.