XML Validator
Validate XML syntax and document well-formedness against W3C standards, detecting unclosed tags, root element violations, and syntax errors.
Quick Answer & Understanding Your Result
An XML Validator verifies XML documents against official W3C XML 1.0 well-formedness rules, locating unclosed tags, mismatched hierarchies, and invalid entity references.
Core W3C Well-Formedness Checks
- Single Root Element: Enforces that exactly one root element encloses all other child tags.
- Matching Open & Close Tags: Verifies case-sensitive opening and closing tags (e.g.
<item>must close with</item>). - Proper Nesting & Quoted Attributes: Checks that overlapping tags (
<a><b></a></b>) are flagged and all attribute values are enclosed in quotes.
Development Applications
- SOAP & Webhook Debugging: Ensuring outgoing XML payloads satisfy strict schema parsers.
- Sitemap Verification: Validating
sitemap.xmlstructure before submitting to Google Search Console.
Paste your XML code above to test syntax validity and detect well-formedness errors instantly.
Formula & Calculation Logic
Technical Specification & ASTDOM verification:
- Checks document tree against W3C XML 1.0 syntax rules.
- Flags unclosed tags and invalid entity references.
Step-by-Step Guide
Paste XML Document
Paste raw XML text into the editor.
Instant Well-Formedness Check
The linter diagnoses syntax errors with exact line and column highlights.
View Verdict & Fix Issues
Receive instant green confirmation or detailed error coordinates to fix.
Worked Examples Table
| Example | Input Values | Calculated Result | Explanation |
|---|---|---|---|
| Valid XML Document | Properly enclosed in single <note> root element with matching tags. | ||
| SOAP API Request Envelope | Provides instant quantitative evaluation for comparative practical analysis. |
Frequently Asked Questions
Evidence-Based Methodology & Authoritative References
W3C XML 1.0 Well-Formedness Specification
W3C XML Schema Definition Language (XSD) 1.1
Standard: ISO / W3C / IETF Authoritative Domain Standard
Formula: WellFormed = ParseXMLDOM(input) → valid: true | valid: false, error, line, col
Last Reviewed: August 21, 2026
Primary Source: W3C XML 1.0 Well-Formedness Specification
Reference Document: W3C XML Schema Definition Language (XSD) 1.1
Computation Privacy: 100% client-side 0ms computation, zero data retention
All algorithms, formatters, and data conversions run 100% locally in your browser following official technical standards (RFC, ISO, W3C). Output should be verified prior to mission-critical production deployment.
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Calculated results are modeled based on standard scientific and mathematical formulas. Please verify with domain-specific technical documentation for specialized applications.