Markup and structure validators
These tools look at documents you publish or feed into parsers: HTML/CSS grammar, feed XML, JSON-LD types, and XSD against an instance. They are not a full W3C or axe-core audit.
Schema.org validation is for JSON-LD shape and required properties on this site, not Google Rich Results guarantees. Config Structure Checker is listed here historically; treat CI and .env tools in the config hub as canonical for deploy files.
HTML, CSS & accessibility(4)
HTML ValidatorCheck HTML markup for syntax errors, unclosed tags, invalid nesting, and W3C compliance issues.CSS ValidatorValidate CSS stylesheet syntax (PostCSS parse). Line/column errors for malformed rules — grammar focus, not browser support.HTML Entities Round-TripBrowser encode/decode round-trip for pasted text snippets.WCAG Contrast CheckerContrast ratio from two hex colors (sRGB luminance).
Feeds & Schema.org(2)
Markdown, XSD & structure(3)
Markdown ValidatorLightweight Markdown heuristics (fences, headings).XSD Schema CheckerValidate XML against an XSD schema. Paste XSD and XML; get line and column errors when the document does not conform.Config Structure CheckerValidate JSON or YAML config: syntax and optional required top-level keys. Paste config, list required keys.
FAQ
- Will this pass Google rich results?
- No validator here is a substitute for Google’s Rich Results Test. Schema.org Validator checks JSON-LD structure and types we support.
- Is the Markdown checker a CommonMark parser?
- No. It flags unbalanced fences and heading spacing. Use it for a quick paste check, not as a spec implementation.