markuplint

Testing & Quality

Reference knowledge for Markuplint HTML linter. Covers violation interpretation, CLI usage, config patterns, and documentation URLs. Auto-loaded when working with HTML linting.

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Source SKILL.md: https://github.com/markuplint/markuplint/blob/HEAD/skills/markuplint/SKILL.md

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Markuplint

Reference knowledge for working with Markuplint.

What is Markuplint

An HTML linter that checks conformance with HTML Standard, WAI-ARIA, and project-specific rules. Supports JSX, Vue, Svelte, Astro, Pug, PHP, and more via parser plugins.

Official site: https://markuplint.dev
GitHub: https://github.com/markuplint/markuplint
Playground: https://playground.markuplint.dev

Reading Violation Messages

Format: message (ruleId) [named-rule]

The attribute name is duplicated (attr-duplication) [html-standard/attr-duplication]

ruleId (attr-duplication) — the base rule. Always present.
named-rule (html-standard/attr-duplication) — preset-defined alias. Present only for named rules. The namespace/ prefix indicates which preset defined it (e.g., a11y/, html-standard/, performance/).
severity — error (exit code 1), warning (exit code 0 by default), or info.

To look up any rule: https://markuplint.dev/docs/rules/{ruleId}

CLI Quick Reference

# Basic lint
npx markuplint "src/**/*.html"

# JSON output (for programmatic use)
npx markuplint "src/**/*.html" --format JSON

# Auto-fix (rules that support it)
npx markuplint "src/**/*.html" --fix

# Preview fixes without writing
npx markuplint "src/**/*.html" --fix-dry-run

# Suppress current violations for gradual adoption
npx markuplint "src/**/*.html" --suppress

# Clean up fixed suppressions
npx markuplint "src/**/*.html" --prune-suppressions

# GitHub Actions annotations
npx markuplint "src/**/*.html" --format GitHub

# Limit output for large projects
npx markuplint "src/**/*.html" --max-count=50

Always quote glob patterns to prevent shell expansion.

Config Patterns

Disable a named rule

{ "rules": { "a11y/html-lang": false } }

Disable all rules in a namespace

{ "rules": { "a11y/*": false } }

Change severity

{ "rules": { "a11y/html-lang": "warning" } }

Element-specific rules

nodeRules — targets the matched element. childNodeRules — targets descendants (add "inheritance": true for all descendants, not just direct children).

Ancestor matching

Use :is(selector *). Do NOT use :closest() — it is deprecated.

{ "selector": "div:is(nav *)" }

Common Issues and Fixes

OGP / Open Graph `property` attribute

The property attribute is not in the HTML spec. See: https://markuplint.dev/docs/rules/invalid-attr#the-open-graph-protocol

`invalid-attr` with frameworks

Install the framework's spec plugin (e.g., @markuplint/react-spec). See: https://markuplint.dev/docs/guides/beyond-html#why-need-the-spec-plugins

`character-reference` false positives with template engines

Some template syntaxes trigger false positives. Disable partially or report: https://markuplint.dev/docs/rules/character-reference

`--init` is interactive only

npx markuplint --init requires terminal input. AI agents should write .markuplintrc directly.

Documentation URLs

Topic	URL
All rules	`https://markuplint.dev/docs/rules`
Specific rule	`https://markuplint.dev/docs/rules/{rule-id}`
Presets	`https://markuplint.dev/docs/guides/presets`
Framework setup	`https://markuplint.dev/docs/guides/beyond-html`
Config properties	`https://markuplint.dev/docs/configuration/properties`
Selectors	`https://markuplint.dev/docs/guides/selectors`
CLI options	`https://markuplint.dev/docs/guides/cli`
FAQ	`https://markuplint.dev/docs/guides/faq`
Migration (v4→v5)	`https://markuplint.dev/docs/migration/v4-to-v5`

Use WebFetch on these URLs when you need current details.