HTML Validator

This tool validates HTML input against HTML5 grammar and constraints, returning a structured report of errors, warnings, and informational notes. It targets frontend developers, QA engineers, content editors, and accessibility specialists who need fast, deterministic feedback on markup quality. By focusing on syntax, nesting, and attribute usage, it helps teams ensure pages render reliably across browsers and assist in accessibility auditing.
Conceptually, the validator parses the input string, applies the W3C HTML validation rules, and reports deviations from the canonical grammar. It flags missing DOCTYPEs, element mismatches, deprecated attributes, unquoted attribute values, and nesting anomalies. Each issue includes line and column positions, the offending code reference, and a human-friendly message to guide fixes.
Unique value lies in deterministic rule sets, consistent results, and easy integration into CI pipelines. The tool supports multiple standards, can operate in text-first mode, and returns machine-friendly results suitable for automated processing. This makes it useful for build processes, pull requests, and content pipelines that require quick validation before deployment.
Core features include input text string, standard selection (HTML5 by default), detailed error and warning lists, severity levels, and suggested fixes. Outputs can be consumed as JSON for automation or as concise human-readable summaries for editors. Typical use cases include code review, CI checks, pre-deployment audits, and compliance verification for web projects.