W3C Markup Validation Service
validator.w3.org
Check HTML and XHTML markup online
Visit website →On this page: About · In their words · Where it fits · Information · Facts · Related tools (6) · FAQ
About W3C Markup Validation Service
The W3C Markup Validation Service is a free, open-source tool that checks the markup of web documents, including HTML and XHTML, using SGML and XML parsers. It supports validation by URI, file upload, or direct input, and offers a wide range of character encodings and document types. This service helps developers ensure their web pages conform to web standards.
Published 2026-08-08 · Links checked 2026-09-06
W3C Markup Validation Service in their own words
“W3C's easy-to-use markup validation service, based on SGML and XML parsers.”
Where W3C Markup Validation Service fits
W3C Markup Validation Service is tagged #html, #validation, #w3c, #web-standards. Each tag links to every listed tool that shares it.
- #html — 4 listed tools share this tag
- #validation — the only listing with this tag so far
- #w3c — the only listing with this tag so far
- #web-standards — the only listing with this tag so far
W3C Markup Validation Service is one of 77 Dev Tools listed on ToolDock. Also in Dev Tools: n8n, Replit, Exa — see the Dev Tools ranking (neutral, stable positions; no paid placement).
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Frequently asked questions
What is W3C Markup Validation Service?
W3C Markup Validation Service is a Dev tool: Check HTML and XHTML markup online. It is listed on ToolDock with a direct link to its official site.
Is W3C Markup Validation Service free?
Yes — W3C Markup Validation Service is listed as free on ToolDock. Pricing label set at listing time; official pricing page linked where verified — see the official website for current details.