CSS Validator W3

This validator checks CSS sources against W3C standards, returning a structured report of syntax errors, unknown properties, and potential compatibility issues. It accepts either a URL pointing to a stylesheet or raw CSS text, enabling quick validation during development, testing, or code review.
Conceptually, the tool tokenizes CSS, verifies grammar rules, validates property names and value formats, and analyzes at-rules, selectors, and media queries for conformance. The output includes precise location data (line and column), error codes, severity levels, and actionable suggestions to guide fixes.
Target users include front-end developers, QA engineers, and technical educators who need reliable CSS validation as part of local workflows or CI integrations. Its value lies in deterministic reports that can be parsed by automation, enabling faster remediation and higher cross-browser reliability.
Key differentiators include dual input modes (URL-based and inline CSS), scalable handling of large stylesheets, and rich structured results suitable for machine processing. It focuses on correctness and traceability, while avoiding automated code changes, so teams maintain full control over edits.
Typical use cases encompass pre-deployment checks in continuous integration, on-demand audits of legacy stylesheets, and learning CSS syntax through concrete error examples. The tool remains strictly about CSS validation, enabling easy integration into other toolchains and pipelines.
Optional linting features surface deprecated properties and potential fallbacks.