HTML validation
The HTML Living Standard describes the behavior of HTML elements and attributes. It is continuously maintained and supersedes all previous HTML specifications, and is sometimes referred to as HTML5.Errors3% Errors indicate conformance errors, and appear when mandatory specification requirements are not met.
Warnings3% Warnings do not indicate conformance errors, but appear when optional specification requirements are not met.
CSS validation
CSS code can be automatically validated against a formal description of the CSS language. The formal description contains the grammar rules of CSS code, along with list of allowed properties.Errors3% Errors indicate conformance errors, and appear when mandatory specification requirements are not met.
Warnings0% Warnings do not indicate conformance errors, but appear when optional specification requirements are not met.
Use of obsolete features
Each version of HTML lists elements and attributes deprecated by the W3C, which may be removed from future versions.Errors0% Errors indicate conformance errors, and appear when mandatory specification requirements are not met.
Warnings0% Warnings do not indicate conformance errors, but appear when optional specification requirements are not met.