> ## Documentation Index
> Fetch the complete documentation index at: https://docs.37audits.com/llms.txt
> Use this file to discover all available pages before exploring further.
# Lighthouse Accessibility Auditor
> Runs the Google Lighthouse Accessibility category on the page and scores it against configurable thresholds
**Accessibility Auditor** — runs the [Google Lighthouse](https://github.com/GoogleChrome/lighthouse) Accessibility category against the monitored page and reports its score: below 90 is a warning and below 50 is a failure, both thresholds set per monitored URL. Every audit Lighthouse lists under the score is a check of its own, with Lighthouse's own description and the offending elements.
The score is the one Lighthouse computes from axe-core, so it matches Chrome DevTools and PageSpeed Insights.
No performance trace is recorded, so the run finishes seconds after the page loads.
This auditor starts a headless Chromium, lets Lighthouse load the page with the desktop preset (or the mobile profile, by preference) and run only its Accessibility audits, and reads the category score from the report. It tells you whether the page works with assistive technology: the Accessibility score Lighthouse computes from its axe-core audits. The check names the lowest-scoring audits of the category, so the report says what to fix first. Lighthouse's Accessibility audits cover colour contrast, image alternative text, form labels, button and link names, heading order, ARIA attributes, language declaration and keyboard focus.
The Lighthouse Accessibility auditor is one of four auditors that share one Lighthouse image; the others are Lighthouse Performance, Lighthouse Accessibility, Lighthouse Best Practices and Lighthouse SEO. Enable the ones a URL needs: each runs its own Lighthouse pass.
## How it works
1. **Thresholds** — reads `formFactor`, `warningBelowScore` and `failBelowScore`. When `failBelowScore` is not lower than `warningBelowScore` the audit fails with a single check (`401`) and Lighthouse does not run.
2. **Lighthouse run** — runs the Lighthouse CLI (version pinned in the image, reported in the `100` check) with the `accessibility` category only, the `desktop` preset or the `mobile` form factor, and the 37AuditsBot user agent. The run has a time budget derived from the audit's remaining time; a page that does not finish loading inside it is an `ERROR` (`500`).
3. **Blocked or unloadable page** — an HTTP 403, 429 or Cloudflare challenge on the document is the platform's blocked response (`590`). Any other Lighthouse runtime error (`NO_FCP`, `PAGE_HUNG`, `DNS_FAILURE`, `ERRORED_DOCUMENT_REQUEST`, …) is an `ERROR` (`500`) that names the error.
4. **Score** — the Accessibility score (0–100) is compared with the thresholds: below `failBelowScore` is `FAIL` (`400`), from `failBelowScore` up to but excluding `warningBelowScore` is `WARNING` (`300`). A category Lighthouse could not score is an `ERROR` (`501`). At or above `warningBelowScore` the audit succeeds (`200`).
5. **Audits** — every audit Lighthouse lists under the Accessibility score becomes a check: a scored audit below Lighthouse's pass mark (0.9) is a `FAIL` whose code is 400 plus the audit's fixed number in this auditor's catalog (52 audits, `410`–`476`); an audit Lighthouse reports without a score or leaves to a manual check is an `INFORMATION` with 100 plus that number. An audit a newer Lighthouse adds gets `490` or `190` until the catalog is updated. Hidden Lighthouse audits and audits that do not apply to the page are not reported. These checks keep their own status but never change the result: the score alone decides it.
6. **Report pin** — every result carries an `INFORMATION` check (`100`) with the Lighthouse and Chrome versions, the device profile, the run duration and Lighthouse's benchmark index, because scores are only comparable between runs of the same Lighthouse version.
The Lighthouse navigation is **not** signed with Web Bot Auth: Lighthouse opens its own browser target and its only header hook adds headers to every request of the page, which breaks cross-origin fetches. Allowlist the 37AuditsBot user agent if the site challenges unsigned bots. With Basic auth the `Authorization` header is sent on every request the page makes, third-party origins included, so prefer allowlisting over credentials for a staging site that loads third-party scripts.
## Preferences
| Key | Type | Default | Description |
| - | - | - | - |
| `formFactor` | string | `desktop` | `desktop` (Lighthouse desktop preset: no CPU slowdown, fast network) or `mobile` (Moto G Power emulation, simulated 4G and 4x CPU slowdown, the PageSpeed Insights default). Any other value falls back to `desktop`. |
| `warningBelowScore` | integer (1–100) | `90` | A Accessibility score below this value produces a `WARNING` (`300`). |
| `failBelowScore` | integer (0–99) | `50` | A Accessibility score below this value produces a `FAIL` (`400`). Must be lower than `warningBelowScore`. |
An invalid value (missing, fractional, outside 0–100) makes the auditor fall back to that preference's default and log a warning. A fail threshold equal to or above the warning threshold is not an invalid value: it makes the audit fail (`401`) until the thresholds are fixed.
## What it audits
Every row maps to one `checkRule*` method and one `CheckCode`.
| CheckCode | Status | When it fires | Recommendation | Why it matters |
| - | - | - | - | - |
| ` elements and elements with `[role="columnheader"/"rowheader"]` have data cells they describe.. Message: ` elements and elements with [role="columnheader"/"rowheader"] have data cells they describe: {display value or item count} (Lighthouse Accessibility audit th-has-data-cells, desktop; reported without a score).` | Screen readers have features to make navigating tables easier. Ensuring table headers always refer to some set of cells may improve the experience for screen reader users. Learn more about table headers ([https://dequeuniversity.com/rules/axe/4.10/th-has-data-cells](https://dequeuniversity.com/rules/axe/4.10/th-has-data-cells)). Found: `{up to three items}`. | — |
| ` elements contain a `` element with `[kind="captions"]`. Message: ` elements contain a element with [kind="captions"]: {display value or item count} (Lighthouse Accessibility audit video-caption, desktop; reported without a score).` | When a video provides a caption it is easier for deaf and hearing impaired users to access its information. Learn more about video captions ([https://dequeuniversity.com/rules/axe/4.10/video-caption](https://dequeuniversity.com/rules/axe/4.10/video-caption)). Found: `{up to three items}`. | — |
| `, ``, etc.) are used to improve the keyboard navigation of the page for assistive technology. Learn more about landmark elements ([https://developer.chrome.com/docs/lighthouse/accessibility/use-landmarks/](https://developer.chrome.com/docs/lighthouse/accessibility/use-landmarks/)). | — |
| `'s do not contain only properly-ordered `` and ` ` groups, `