Available rules

Rules with are enabled by htmlvalidate:recommended.
Rules with are enabled by htmlvalidate:document.

close-attr Disallow end tags from having attributes
close-order Require elements to be closed in correct order
deprecated Disallow usage of deprecated elements
doctype-html Require usage of "html" doctype
element-name Disallow invalid element names
meta-refresh Require meta refresh to have 0 second delay
no-conditional-comment Disallow usage of conditional comments
no-deprecated-attr Disallow usage of deprecated attributes
no-dup-attr Disallow duplicated attributes
no-dup-class Disallow duplicated classes
no-dup-id Disallow duplicated IDs
no-raw-characters Disallow the use of unescaped special characters
no-style-tag Disallow usage of <style> tag
no-unknown-elements Disallow usage of unknown elements
prefer-button Prefer to use <button> instead of <input> for buttons
prefer-tbody Prefer to wrap <tr> inside <tbody>
require-sri Require SRI for resources
unrecognized-char-ref Disallow unrecognized character references

Content model

attribute-allowed-values Validate permitted attribute values
element-permitted-content Validate permitted content from content model
element-permitted-occurrences Validate permitted number of occurrences from content model
element-permitted-order Validate required order from content model
element-required-attributes Ensure required attributes are set
element-required-content Ensure required elements are present

Accessibility

empty-heading Require headings to have textual content
empty-title Require title to have textual content
input-missing-label Require input to have label
wcag/h30 WCAG 2.1 H30: Providing link text
wcag/h32 WCAG 2.1 H32: Providing submit buttons
wcag/h36 WCAG 2.1 H36: Require alt text on images used as submit buttons
wcag/h37 WCAG 2.1 H37: Using alt attributes on img elements
wcag/h67 WCAG 2.1 H67: Using null alt text and no title attribute on img elements for images that AT should ignore

SEO

long-title Require title not to have too long text

Style

attr-case Require a specific case for attribute names
attr-quotes Require attribute quoting
attribute-boolean-style Require a specific style for boolean attributes
class-pattern Require classes to match a specific pattern
element-case Require a specific case for element names
id-pattern Require IDs to match a specific pattern
no-implicit-close Require elements with optional end tags to be explicitly closed
no-inline-style Disallow inline style
no-trailing-whitespace Disallow trailing whitespace
void Disallow void element with content

Document

These rules is to be used on full documents.

heading-level Require headings to start at h1 and be sequential
missing-doctype Require document to have a doctype
no-missing-references Require all element references to exist