HTML Markup Validator Pro
Paste HTML or drop a file and get a list of problems, each with its line, column and the markup that triggered it. It checks a fixed set of common rules in your browser rather than the full HTML specification. Free preview · Pro required to export. Check up to 3,000 characters of markup free. Pro removes this limit and adds downloadable reports.
Free preview · Pro required to export. Check up to 3,000 characters of markup free. Pro removes this limit and adds downloadable reports.
Why use this tool?
- Unclosed tags, duplicate ids and blocks inside paragraphs are easy to introduce by hand and hard to spot by eye.
- Missing alt text, empty links and skipped heading levels hurt screen-reader users, and a checker can find them in seconds.
- Browsers repair broken markup silently, so a page can look fine and still have structure you did not intend.
- Sometimes the document is private, such as a draft, an email template or an internal page, and you do not want to upload it to an online checker.
How to use Markup Validator
- Paste a page or a fragment into the Markup box, or click Sample to see an example full of mistakes.
- Alternatively, drop an .html, .htm, .xhtml, .vue or .svg file of up to 4 MB onto the drop zone.
- Read the line beneath the box: it says whether the input was checked as a whole document or a fragment.
- In Findings, use the Errors, Warnings and Notes chips to show or hide each severity.
- Fix the markup at the reported line and column and the list updates a moment after you stop typing.
- Click Copy report or the download button to save the findings as validation-report.txt.
Features
- Rules grouped as Document, Tags, Attributes, Structure and Text
- Three severities: errors, warnings and notes
- Line and column for every finding, plus a short excerpt of the offending tag
- Document-level rules applied only when the input contains a full page
- Counts of errors, warnings and notes
- File drop for .html, .htm, .xhtml, .vue and .svg
- A text report for copying or downloading
Supported formats
Accepts HTML as pasted text or as an .html, .htm, .xhtml, .vue or .svg file up to 4 MB. Output is an on-screen list and a plain-text report.
Tips
- Clear the errors first; warnings describe valid markup that tends to cause trouble later, and notes are advice.
- Paste a full page, starting with <html>, to include the doctype, title, lang, charset and viewport checks. A fragment skips those.
- The rule list under What this checks shows exactly what is covered, so you know what a clean result does and does not mean.
- For full conformance to the HTML specification, follow up with the W3C Nu Html Checker linked in the tool.
Frequently asked questions
Is this the same as the W3C validator?
No. It checks the rules listed on the page, the ones hand-written markup most often breaks, and does not implement the whole specification. The W3C checker is the authority for full conformance.
Is my HTML uploaded?
No. The check runs in your browser tab and the markup is not sent to a server.
Why is it not asking for a doctype on my snippet?
Input without an <html> element is treated as a fragment, and rules about doctype, title, language, encoding and viewport are held back for fragments.
What is the largest file I can check?
4 MB. Larger files are refused with a message, though you can still paste a section of one into the text box.
Does a result with no errors mean the page is valid?
It means none of the rules this tool checks were broken. Pages can still fail rules it does not cover, so use it as a first pass.
What do warnings and notes mean?
Warnings are valid markup that is likely to cause problems, and notes are lower-priority suggestions. Only errors make the summary say the markup is not clean.
Can I try this Pro tool without an account?
Yes. Check up to 3,000 characters of markup free. Pro removes this limit and adds downloadable reports. Your own input is processed locally in your browser.
Will upgrading keep my work?
Checkout and login open in a separate tab. Keep the workspace open to retain inputs, settings and previews. Files stay in that tab only; keep the originals in case you close or reload it. Export access is checked with the server after payment.
Your files are processed directly in your browser and are not uploaded to HubToolify's servers.