HTML Tag Validator
Fix broken USA email and CMS HTML in seconds. Paste fragment like <div><p>Hello</div>, get unclosed/mismatched list plus count instantly offline with no signup with tag-balance checks nesting validation plus attribute quoting rules for pages emails and templates across development QA and CMS workflows daily plus email-Outlook rules and CMS bloat cleanup for developers editors agencies students and archive migrations.
Quickly check HTML for unclosed or mismatched tags instantly in your browser. Free online HTML tag validator — finds mismatched and missing closing tags.
Calculator Inputs
About HTML Validator
Fix broken USA email and CMS HTML in seconds. Paste fragment like <div><p>Hello</div>, get unclosed/mismatched list plus count instantly offline with no signup with tag-balance checks nesting validation plus attribute quoting rules for pages emails and templates across development QA and CMS workflows daily plus email-Outlook rules and CMS bloat cleanup for developers editors agencies students and archive migrations.
Stack tracks opens, reports never-closed, wrong-order, orphan closes. Void img/br/input + self-close handled. Balance only, not full W3C.
Paste, read issues lines, fix order. All local.
Example: div>pHello/div → unclosed p.
Email: Outlook strict — balance first.
Limits: No attr/spec check. Use W3C for conformance.
Balance checks: Every opened div, section, and table needs its closer — one missing tag collapses layouts site-wide. Austin devs shipping $90,000 sites validate before staging deploys catch it on 09/22/2026.
Email template hell: Chicago editors fixing $4,000 newsletter templates validate table nesting Outlook demands. One unclosed td breaks rendering for 40 percent of subscribers.
Attribute quoting: Unquoted values break on spaces and special characters. Seattle QA gating $2M releases flags bare attributes blocking strict parsers.
CMS content: Miami agencies auditing pasted Word markup strip proprietary tags that bloat pages 300 percent. Denver students learn semantic tags validators reward.
Archive health: New York publishers validating $500,000 article archives batch-check decades of markup before migrations corrupt history.
SOC audits: Boston startups passing $1M security reviews validate markup as part of hardened build pipelines. Seattle-adjacent staging gates catch injection-shaped anomalies early on 09/22/2026.
Inbox reach: San Francisco emails reaching 2M subscribers validate table layouts Litmus-style before send. Phoenix restaurants publishing menus confirm mobile email renders drive foot traffic.
Intranet scale: Dallas intranets serving 10,000 staff validate templates once to fix every department page. Atlanta portfolios loading galleries validate lazy-load markup that breaks silently.
School publishing: Philadelphia schools posting $20,000 lunch programs keep accessible tables screen readers parse for parents.
Where it is used
Devs debugging hand HTML, marketers cleaning Mailchimp templates, bloggers fixing WordPress embeds, students learning nesting, and QA pre-paste sanity checks Austin devs ship $90,000 sites, Chicago editors fix $4,000 email templates, Miami agencies audit client pages, Denver students learn markup, Seattle QA gates $2M releases, and New York publishers validate $500,000 article archives Boston startups pass $1M SOC audits, San Francisco emails reach 2M inboxes, Dallas intranets serve 10,000 staff, Atlanta portfolios load galleries, Phoenix restaurants publish menus, and Philadelphia schools post $20,000 lunch programs.
How to use the HTML Validator
- HTML to check — enter the value (e.g. <div><p>Hello</div>).
- Calculate — press the Calculate button to see the result instantly above.
Formula
regex tags → stack push open, pop on match close; void/self-close skip; leftover = unclosed.
Examples
Missing p
Clean
Orphan close
Frequently Asked Questions
- Does a clean result mean valid HTML?
- Not necessarily — this checks structural balance only. Attributes, nesting rules, and document structure still follow the HTML spec, which a fuller validator would confirm.
- Are HTML comments handled?
- Comments (<!– –>) are ignored, which is fine for tag balancing since they have no open/close tags that affect nesting.
- Warnings versus errors?
- Errors break parsing or rendering; warnings flag deprecated but working markup. Fix errors first, schedule warnings.
- Email HTML stricter?
- Yes — Outlook uses Word rendering with table-only layouts. Validate against email rules, not modern web rules.
- Stored anywhere?
- No. Validation runs locally in your browser. No markup is uploaded or stored.