Lightweight static HTML accessibility linter for WCAG 2.2

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Project description

Accessibility Champion

Accessibility Champion is a lightweight, static accessibility linter for HTML files. It helps identify common WCAG 2.2 AA violations in your markup and generates an accessibility score to help developers triage and fix issues quickly.

The linter uses Python's HTMLParser with a rule-registry architecture: a thin dispatcher forwards parse events to focused rule classes, keeping each check isolated and easy to extend.

Quick Start

Run the linter against any HTML file to get a human-readable text report:

python3 a11y_lint.py path/to/your/file.html

Try the included demo fixtures:

python3 a11y_lint.py demo/broken_page.html   # exits 1 — many violations
python3 a11y_lint.py demo/passing_page.html  # exits 0 — score 100/100

CLI Options

Flag	Description
`--json`	Output results as a JSON array (one entry per file)
`--fragment`	Treat input as an HTML fragment; skip full-page landmark and single-`<h1>` checks
`--full-page`	Force full-page mode even when `<html>` / `<body>` tags are absent

Auto-detection: When neither --fragment nor --full-page is passed, the linter treats markup as a fragment unless it contains an <html> or <body> tag. Full-page landmark checks (<main>, <header>, <nav>, <footer>, single <h1>) only run in full-page mode.

# JSON output for CI
python3 a11y_lint.py path/to/your/file.html --json

# Lint a partial HTML snippet (e.g., a component template)
python3 a11y_lint.py path/to/fragment.html --fragment

Exit Codes

0 — no violations found across all linted files
1 — one or more violations found, or a file could not be read

Any violation severity (including minor) causes a non-zero exit when --json is not used for machine parsing.

Output Format

Text Report

The default text output provides a score out of 100, followed by violations grouped by severity. Each violation includes:

id — stable rule identifier (e.g., image-alt, form-group-fieldset)
line — source line number
message — human-readable description
fix — suggested remediation
wcag — relevant WCAG success criterion

JSON Report

[
  {
    "file": "demo/broken_page.html",
    "score": 0,
    "violations": [
      {
        "id": "html-has-lang",
        "severity": "serious",
        "line": 2,
        "message": "<html> tag is missing a lang attribute",
        "fix": "Add lang=\"en\" (or appropriate language code) to the <html> tag",
        "wcag": "3.1.1 Language of Page"
      },
      {
        "id": "image-alt",
        "severity": "critical",
        "line": 14,
        "message": "<img> is missing an alt attribute",
        "fix": "Add alt=\"[description]\" for informational images, or alt=\"\" role=\"presentation\" for decorative ones",
        "wcag": "1.1.1 Non-text Content"
      }
    ]
  }
]

Programmatic API

from a11y_lint import check_html, score

violations = check_html(source)                  # auto-detect fragment vs full page
violations = check_html(source, fragment=True) # force fragment mode
total = score(violations)

Scoring Model

The Accessibility Score starts at 100 and deducts points based on severity:

Severity	Points	Examples
Critical	−20	Missing `alt`, unlabelled form controls, buttons without accessible names
Serious	−10	Missing `lang`, duplicate IDs, generic link text, missing `iframe` title
Moderate	−5	Skipped heading levels, missing `<main>`, ungrouped radio/checkbox sets
Minor	−2	Missing `autocomplete` on personal-data fields, optional landmark regions

The score is clamped to a minimum of 0.

Current Checks

Pillar 1 — Perceivable

Rule ID	What it checks
`html-has-lang`	`<html>` missing `lang` attribute
`image-alt`	`<img>` missing `alt` attribute
`image-alt-quality`	Generic `alt` text (`image`, `photo`, `logo`, etc.)
`no-autoplay`	`<video>` / `<audio>` with `autoplay`
`video-captions`	`<video>` missing `<track kind="captions">`
`audio-transcript`	`<audio>` without nearby transcript link/text (heuristic)
`document-title`	Full page missing non-empty `<title>` in `<head>`

Pillar 2 — Operable

Rule ID	What it checks
`button-name`	`<button>` with no accessible name (text, `aria-label`, child `<img alt>`, or `<svg><title>`)
`link-name`	`<a>` with generic text (`click here`, `read more`, `here`, `more`, etc.)
`focus-visible`	`outline: none` / `outline: 0` in CSS without a matching `:focus` / `:focus-visible` fallback rule
`skip-link`	Full page with `<nav>` missing a skip-to-main-content link
`tabindex-positive`	Any `tabindex` value greater than 0
`button-type-missing`	`<button>` inside `<form>` without explicit `type` attribute
`target-blank-no-warning`	`target="_blank"` without accessible new-window warning

Focus-outline analysis parses CSS rule blocks inside <style> elements and inline style="" attributes. It matches base selectors (e.g., .btn) to companion :focus-visible rules that restore a visible outline.

Pillar 3 — Understandable

Rule ID	What it checks
`input-unlabelled`	Form control has no `id`, is not wrapped in `<label>`, and has no `aria-label`
`input-missing-label`	Control has an `id` but no matching `<label for="...">`
`placeholder-as-label`	`placeholder` used without a real label or `aria-label`
`input-autocomplete`	Personal-data inputs (`email`, `password`, `tel`, or `name`/`address`-like fields) missing `autocomplete`
`aria-invalid-no-desc`	`aria-invalid="true"` without `aria-describedby` pointing to an error element

Applies to <input>, <select>, and <textarea>.

Pillar 4 — Robust & Semantic Structure

Rule ID	What it checks
`duplicate-id`	Duplicate `id` attribute values
`form-group-fieldset`	Multiple radio/checkbox inputs sharing a `name` not wrapped in `<fieldset>` + `<legend>` (one violation per group)
`aria-describedby-missing-target`	`aria-describedby` references an `id` that does not exist
`aria-labelledby-target`	`aria-labelledby` references an `id` that does not exist
`heading-order`	Skipped heading levels (e.g., `<h1>` → `<h3>`)
`heading-single-h1`	More than one `<h1>` on a full page
`frame-title`	`<iframe>` missing `title`
`table-th`	Data table missing `<th>` header cells
`table-caption`	Data table missing `<caption>`
`missing-main`	Full page missing `<main>` landmark
`missing-header-landmark`	Full page missing `<header>` / `role="banner"`
`missing-nav-landmark`	Full page missing `<nav>` / `role="navigation"`
`missing-footer-landmark`	Full page missing `<footer>` / `role="contentinfo"`

Presentation tables (role="presentation") are exempt from table header/caption checks.

Architecture

a11y_lint.py      CLI entry point; thin HTMLParser dispatcher
a11y_context.py   ParseContext (shared state) and TagAttrs helpers
a11y_rules.py     Individual A11yRule classes registered via all_rules()
a11y_focus.py     CSS rule-block parser for focus-outline checks

To add a new check, create a class extending A11yRule in a11y_rules.py with on_starttag, on_endtag, on_data, and/or finalize hooks, then register it in all_rules().

Running Tests

python3 -m unittest test_a11y_lint -v

The suite covers fixture pages, individual rules, CLI behavior, fragment mode, and edge cases (30 tests). Every new rule must include tests that verify both failing and passing markup.

Limitations

⚠️ This is a static linter and does not replace manual accessibility review.

While it catches a meaningful share of common HTML accessibility issues, automated tooling cannot validate:

Interaction intent — Does a custom widget actually behave like its native equivalent?
Meaningful text — Is the alt text actually descriptive in context?
Keyboard navigation — Are there keyboard traps or focus-management issues?
Visual contrast — Real contrast ratios require rendering the DOM and CSS.

Always supplement this tool with screen reader testing, keyboard navigation audits, and dynamic tools like axe-core.

Demo Fixtures

File	Purpose
`demo/broken_page.html`	Intentionally broken markup; demonstrates linter output
`demo/passing_page.html`	Accessible page that scores 100/100
`demo/expected_output.txt`	Reference text output for `broken_page.html`

Project Layout

a11y_lint.py — CLI entry point and thin HTML parser dispatcher
a11y_context.py — Shared parse context and attribute helpers
a11y_rules.py — Individual accessibility rule implementations
a11y_focus.py — CSS focus-outline checks for <style> blocks and inline styles
demo/broken_page.html — Fixture demonstrating failing checks
demo/passing_page.html — Fixture demonstrating passing checks
test_a11y_lint.py — Automated test suite
SKILL.md — AI agent integration guidelines for accessibility audit workflows

Roadmap

See ROADMAP.md for the phased plan to expand coverage toward full WCAG-aligned auditing (static rules → CSS analysis → axe-core integration).

Contributing

Keep changes small and surgical.
Add new rules as A11yRule subclasses in a11y_rules.py; register them in all_rules().
Add tests to test_a11y_lint.py for both failing and passing markup.
Prefer the HTML parser over regular expressions for structural checks.
Update this README when adding new rule IDs, CLI flags, or architectural changes.

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0.4.0

Jul 9, 2026

0.3.0

Jul 9, 2026

0.2.0

Jul 1, 2026

0.1.3

Jun 28, 2026

0.1.2

Jun 28, 2026

0.1.1

Jun 28, 2026

This version

0.1.0

Jun 28, 2026

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accessibility-champion 0.1.0

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Project description

Accessibility Champion

Quick Start

CLI Options

Exit Codes

Output Format

Text Report

JSON Report

Programmatic API

Scoring Model

Current Checks

Pillar 1 — Perceivable

Pillar 2 — Operable

Pillar 3 — Understandable

Pillar 4 — Robust & Semantic Structure

Architecture

Running Tests

Limitations

Demo Fixtures

Project Layout

Roadmap

Contributing

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