a11y-toolkit

a11y-toolkit — the accessibility layer for AI coding agents

23 MCP tools, 5 prompts and a skill covering the whole WCAG 2.2 loop: audit, fix, document, watch, hand off. 51 of 55 A/AA criteria carry automated signals (93%), every finding ships with a concrete remediation your agent can apply, and the rendered tools run on whichever browser you have — Chromium, Firefox, WebKit, Chrome or Edge.

The European Accessibility Act is in force since June 2025, ADA suits keep landing, and AI agents now write most of the web. A scan is not a defence: the machine finds, the human signs.

What no other a11y tool gives an agent

Capability	axe-core / Lighthouse / pa11y	a11y-toolkit
Text contrast over images and gradients (pixel sampling of the real background)	✗	✓
Form error testing: fills invalid data, really submits, judges what happens	✗	✓
Keyboard traps: real Tab walk + Escape-release test, plus focus/input-triggered navigation	✗	✓
Infinite-scroll audit: focus survival, announcements, feed end	✗	✓
Reflow at 320px and the WCAG text-spacing override, measured	✗	✓
Screen reader transcript: what a blind user hears, linearized	✗	✓
Tooltips that ignore Escape caught by actually hovering (1.4.13)	✗	✓
Legal statements for the EAA / RD 1112/2018, in Spanish and English	✗	✓
An evidence pack a human can countersign — hashes, matrix, empty signature block	✗	✓
Runs with zero dependencies at core, speaks es/en, any browser you have	heavy runtimes	✓

The tools (23)

Audit

Tool	What it does
a11y_audit_url	Express static audit of a URL or raw HTML: 40+ signals across 51 WCAG criteria with a weighted 0-100 score. Covers alt, accessible names, labels, autocomplete (1.3.5), ARIA validity (roles/refs/values), headings, zoom, lang, captions, autoplay, link purpose (2.4.4), list structure, duplicate ids/accesskeys, placeholder-only labels, fieldset/legend for radio groups, label quality, required-field indication, financial forms without confirmation (3.3.4), character-key shortcuts (2.1.4), drag handlers (2.5.7), status regions (4.1.3), heading quality (2.4.6), sensory instructions (1.3.3), orientation lock (1.3.4), images of text (1.4.5), consistent help (3.2.6), site-level nav consistency (3.2.3) and multiple ways (2.4.5).
a11y_audit_dom	Rendered audit in Chromium/Firefox/WebKit: computed text contrast with alpha compositing (1.4.3), target size 24×24 (2.5.8 — new in WCAG 2.2), focus indicator (2.4.7), :focus/:hover state contrast, text spacing override (1.4.12 — injects WCAG spacing, counts clipped texts), color-only links (1.4.1), DOM-vs-visual order (1.3.2), looping animations (2.2.2), open shadow DOM traversed, same-origin iframes scanned. Accepts auth_state for behind-login auditing and browser for engine selection.
a11y_forms	Form error testing (3.3.1/3.3.3): fills validatable fields with invalid data, really submits, judges whether errors are identified and announced in the post-submit DOM. Native browser validation counts (unless novalidate).
a11y_keyboard	Keyboard traps (2.1.2) with real Tab walking + cycle detection + Escape-release test. Also detects focus-triggered navigation (3.2.1) and input-triggered navigation (3.2.2).
a11y_scroll	Infinite-scroll audit: does focus survive each batch? Is new content announced (4.1.3)? Does the feed end or offer load-more?
a11y_reflow	320px reflow (1.4.10): real horizontal scroll + overflowing elements.
a11y_html_validate	W3C Nu validator (validator.w3.org/nu): doctype, encoding, structural validity, authoritative alt/lang/role findings mapped to criteria. Self-hosted vnu supported.
a11y_hover	Hover dismissibility (1.4.13): finds tooltip/overlay candidates, hovers each, and tests whether Escape dismisses the result.
a11y_sr_transcript	Screen reader transcript: what a blind user HEARS on this page — linearized accessibility tree as prose. The single best tool for "does this page make sense without sight?"

Fix

Tool	What it does
a11y_autofix	Deterministic safe fixes: unblock zoom (1.4.4), autocomplete tokens (1.3.5), missing lang, empty title, accessible form-error layer (aria-invalid + describedby + attribute-derived suggestions — skips forms with their own handling). Judgment fixes returned as no_aplicados with remediation.
a11y_contrast_pair	Exact ratio + verdicts 1.4.3/1.4.6/1.4.11. Accepts #hex, rgb(), hsl(), CSS names; alpha composites. Suggests nearest passing color.
a11y_contrast_image	Text over images: pixel-level sampling → worst/median/p95 ratio, % area passing AA, hostile-zone grid.
a11y_suggest_color	Nearest opaque color reaching the target ratio.

Document

Tool	What it does
a11y_generate_declaration	Legal statement: RD 1112/2018 art. 10 or European Accessibility Act (EAA). es/en. The document is itself accessible.
a11y_badge	Honest SVG badge: score, date, "automated screening" scope — never claims conformance.
a11y_criterion	Explains any WCAG 2.2 criterion: what it requires, typical failures, which tool verifies it.

Watch

Tool	What it does
a11y_snapshot	Interactive elements + real tab order + computed accessibility tree (what a screen reader announces).
a11y_diff	Regression diff between snapshots: interactives, focus order, tree changes.
a11y_diff_urls	Snapshot two URLs and diff (staging vs production).
a11y_aria_live_snippet	Injectable monitor logging every aria-live announcement.

Hand off

Tool	What it does
a11y_evidence	Countersignature-ready evidence pack: full criteria matrix (fail/review/not-flagged/agent-verified/manual-only), SHA-256-hashed artifacts with embedded report bodies (self-verifying), empty signature block tied to the pack hash, measured values (e.g. "3.91:1") surfaced per criterion. Spec: docs/evidence-pack-schema.md.
a11y_disprove	Disprover pattern: re-runs the audit against the live page and marks each finding confirmed or rejected — findings that don't reproduce are rejected with the reason. Returns a fresh score over confirmed findings only.
a11y_ledger	Coverage ledger: persistent record of what has been audited, when, and with what result. Actions: record, gaps, summary. Accumulates across runs.

5 prompts: audit-page, fix-contrast, pre-deploy-check (GO/NO-GO), declaration-eaa, conformance-wcagem (three-tier WCAG-EM ladder).

Install

mcp-name: io.github.kinti/a11y-toolkit · PyPI: a11y-toolkit · Zenodo DOI: 10.5281/zenodo.22843722

Works with any MCP-capable client — Claude Code/Desktop, Cursor, Windsurf, VS Code, Codex CLI, OpenCode, ZCode, Zed, Cline, Continue, Kimi Code… See docs/clients.md for every verified config format.

claude mcp add a11y-toolkit -- uvx --from a11y-toolkit a11y-toolkit-mcp

Or with JSON config:

{
  "mcpServers": {
    "a11y-toolkit": {
      "command": "uvx",
      "args": ["--from", "a11y-toolkit", "a11y-toolkit-mcp"],
      "timeoutMs": 60000
    }
  }
}

Rendered tools use Playwright if present and accept a browser parameter (auto, chromium, firefox, webkit, chrome, msedge — auto-detects the first available). Accept auth_state (Playwright storage_state path) to audit behind login. Everything else works with zero dependencies.

The skill

git clone https://github.com/kinti/a11y-toolkit && cd a11y-toolkit
./skill/install-skill.sh     # → ~/.zcode/skills and ~/.claude/skills

CLI — same engine, one command

a11ytoolkit audit --url https://example.com --pages 5   # sitemap-first crawl
a11ytoolkit pair "#1f2328" "#fbfaf7"                    # contrast
a11ytoolkit image hero.jpg --text "#fff" --region 120,40,420,90
a11ytoolkit forms https://mysite/contact                # form errors
a11ytoolkit kbd https://mysite                          # keyboard traps + 3.2.1/3.2.2
a11ytoolkit reflow https://mysite                       # 320px reflow
a11ytoolkit scroll https://medium.com/feed              # infinite scroll
a11ytoolkit validate --url https://example.com          # W3C Nu
a11ytoolkit hover https://mysite                        # tooltip dismissibility
a11ytoolkit fix --file page.html -o fixed.html          # safe autofix
a11ytoolkit declaration --entidad "Acme" --url https://… --estado parcial --marco eaa
a11ytoolkit snapshot https://mysite --out before.json   # before deploy
a11ytoolkit diff before.json after.json                 # after deploy
a11ytoolkit evidence audit.json -o pack.json            # countersignature-ready pack
a11ytoolkit disprove --url https://mysite               # re-verify findings
a11ytoolkit budget --budget budget.json --audit audit.json  # only NEW findings block
a11ytoolkit sarif --from-audit audit.json -o a11y.sarif # GitHub code scanning
a11ytoolkit badge --score 92 --out badge.svg            # honest SVG

Coverage: 51 of 55 WCAG 2.2 A/AA criteria (93%)

With automated signal	Manual-only (genuinely human)
1.1.1, 1.2.2, 1.2.3, 1.2.5, 1.3.1–1.3.5, 1.4.1–1.4.5, 1.4.10–1.4.13, 2.1.1, 2.1.2, 2.1.4, 2.2.1, 2.2.2, 2.4.1–2.4.7, 2.4.11, 2.5.1–2.5.4, 2.5.7, 2.5.8, 3.1.1, 3.1.2, 3.2.1–3.2.4, 3.2.6, 3.3.1–3.3.4, 3.3.8, 4.1.2, 4.1.3	1.2.1 (audio transcripts), 1.2.4 (live captions), 2.3.1 (flash detection), 3.3.7 (redundant entry)

The 4 manual-only criteria each have a knowledge entry (a11y_criterion) telling the agent exactly how to verify them by hand. The boundary is printed on every report.

Free online analyzer

I also run a11y.jquin.net, a free online analyzer with the same engine — full report, badge, evidence-pack download. Every report ends at the exact boundary where a qualified human begins, which is the point.

Validated against real pages

Benchmarked against axe-core 4.10 on real pages monthly (methodology and results). Found a real WCAG failure on gov.uk that axe does not report (blue button at 3.91:1, manually verified). Drove out our own false positives (hidden skip links, honeypot fields, single-context generic links, image-alt accname — each with a regression fixture).

Why I built this

I have been auditing websites for accessibility since 2003. In twenty years the tools got faster and the failures stayed the same: the same missing alt text, the same keyboard traps, the same forms that swallow your work. When AI agents started writing most of the web, the audit gap stopped being a staffing problem and became an infrastructure one.

So I built the tool I always wanted next to me on an audit. Not another scanner — scanners exist. A toolkit that does half the work, says exactly where it stops, and packages the rest for the person who signs. The gov.uk failure you read about above is not a synthetic benchmark case: this engine found it, and I confirmed it with my own eyes before writing it down.

If it saves you an afternoon, leave a star — it genuinely helps the next auditor find it. If it doesn't, open an issue and tell me what is missing.

Honesty, built in

Every audit says: automation covers 93% of A/AA criteria; the rest needs a human. The audit-page prompt and the skill have the agent check what it can (keyboard, focus, zoom, announced errors) using the manual checklist. A filter, not a verdict. The remaining human work is priced per criterion — MIN 23 (read and confirm), MED 19 (verify in the browser), MAX 13 (real interaction and judgment); full table. And the evidence pack is the handoff object for the person who signs, screen reader transcript included, so the reviewer sees what a blind user hears.

Security & scope

A local tool: runs on your machine as your user. a11y_audit_url accepts http/https only (no file:// — use --file/html for local HTML). a11y_html_validate in html mode POSTs content to the W3C service (url mode shares only the URL; self-hosted vnu supported). path/output_path read/write local paths — use it in MCP clients you trust.

Development

python3 tests/test_contrast.py && python3 tests/test_audit.py && python3 tests/test_v32.py \
  && python3 tests/test_dom.py && python3 tests/test_cli.py && python3 tests/test_solido.py \
  && python3 tests/test_mcp.py

tests/test_dom.py self-skips without Playwright. tests/test_solido.py enforces the design invariants (catalog parity, version alignment, count coverage, hostile-HTML fuzz). Releases: make release V=X.Y.Z — bumps, gates, tags and pushes atomically.

Roadmap

Done recently: rendered audit with shadow DOM and state contrast, form error testing plus autofix, keyboard traps, infinite scroll, reflow, the W3C Nu integration, SARIF and error budgets, the evidence pack (spec published, self-verifying), sitemap crawling, behind-login auditing, browser auto-detection, the screen reader transcript, and per-criterion effort pricing. The full history lives in the changelog.

Next, roughly in this order:

• Attestation interlock: let an external auditor's countersignature reference the evidence pack by hash (their schema, my side adapts)
• Publish the monthly axe-core benchmark results from CI, run over real pages
• Screen-reader transcript cross-checks against NVDA and VoiceOver output
• More verified client configs (JetBrains AI, Gemini CLI), same treatment as docs/clients.md

Author

Jesús Quintana Fernández (jquin.net) — SEO/GEO consultant and web-accessibility practitioner since 2003. MIT © 2026.