Each ARIA `role` supports a specific subset of `aria-*` attributes. Mismatching these invalidates the `aria-*` attributes. [Learn how to match ARIA attributes to their roles](https://dequeuniversity.com/rules/axe/4.7/aria-allowed-attr).

`[aria-*]` attributes match their roles

Assistive technologies, like screen readers, work inconsistently when `aria-hidden="true"` is set on the document `<body>`. [Learn how `aria-hidden` affects the document body](https://dequeuniversity.com/rules/axe/4.7/aria-hidden-body).

`[aria-hidden="true"]` is not present on the document `<body>`

Assistive technologies, like screen readers, can't interpret ARIA attributes with invalid names. [Learn more about valid ARIA attributes](https://dequeuniversity.com/rules/axe/4.7/aria-valid-attr).

`[aria-*]` attributes are valid and not misspelled

Assistive technologies, like screen readers, can't interpret ARIA attributes with invalid values. [Learn more about valid values for ARIA attributes](https://dequeuniversity.com/rules/axe/4.7/aria-valid-attr-value).

`[aria-*]` attributes have valid values

Canonical links suggest which URL to show in search results. [Learn more about canonical links](https://developer.chrome.com/docs/lighthouse/seo/canonical/).

Document has a valid `rel=canonical`

A character encoding declaration is required. It can be done with a `<meta>` tag in the first 1024 bytes of the HTML or in the Content-Type HTTP response header. [Learn more about declaring the character encoding](https://developer.chrome.com/docs/lighthouse/best-practices/charset/).

Properly defines charset

Low-contrast text is difficult or impossible for many users to read. [Learn how to provide sufficient color contrast](https://dequeuniversity.com/rules/axe/4.7/color-contrast).

Background and foreground colors do not have a sufficient contrast ratio.

Search engines may use `href` attributes on links to crawl websites. Ensure that the `href` attribute of anchor elements links to an appropriate destination, so more pages of the site can be discovered. [Learn how to make links crawlable](https://support.google.com/webmasters/answer/9112205)

Links are crawlable

Cumulative Layout Shift measures the movement of visible elements within the viewport. [Learn more about the Cumulative Layout Shift metric](https://web.dev/cls/).

Cumulative Layout Shift

Deprecated APIs will eventually be removed from the browser. [Learn more about deprecated APIs](https://developer.chrome.com/docs/lighthouse/best-practices/deprecations/).

Avoids deprecated APIs

Specifying a doctype prevents the browser from switching to quirks-mode. [Learn more about the doctype declaration](https://developer.chrome.com/docs/lighthouse/best-practices/doctype/).

Page has the HTML doctype

The title gives screen reader users an overview of the page, and search engine users rely on it heavily to determine if a page is relevant to their search. [Learn more about document titles](https://dequeuniversity.com/rules/axe/4.7/document-title).

Document has a `<title>` element

All focusable elements must have a unique `id` to ensure that they're visible to assistive technologies. [Learn how to fix duplicate `id`s](https://dequeuniversity.com/rules/axe/4.7/duplicate-id-active).

`[id]` attributes on active, focusable elements are unique

Errors logged to the console indicate unresolved problems. They can come from network request failures and other browser concerns. [Learn more about this errors in console diagnostic audit](https://developer.chrome.com/docs/lighthouse/best-practices/errors-in-console/)

Browser errors were logged to the console

First Contentful Paint marks the time at which the first text or image is painted. [Learn more about the First Contentful Paint metric](https://developer.chrome.com/docs/lighthouse/performance/first-contentful-paint/).

First Contentful Paint

Screen reader users rely on frame titles to describe the contents of frames. [Learn more about frame titles](https://dequeuniversity.com/rules/axe/4.7/frame-title).

`<frame>` or `<iframe>` elements do not have a title

Users are mistrustful of or confused by sites that request their location without context. Consider tying the request to a user action instead. [Learn more about the geolocation permission](https://developer.chrome.com/docs/lighthouse/best-practices/geolocation-on-start/).

Avoids requesting the geolocation permission on page load

Properly ordered headings that do not skip levels convey the semantic structure of the page, making it easier to navigate and understand when using assistive technologies. [Learn more about heading order](https://dequeuniversity.com/rules/axe/4.7/heading-order).

Heading elements appear in a sequentially-descending order

hreflang links tell search engines what version of a page they should list in search results for a given language or region. [Learn more about `hreflang`](https://developer.chrome.com/docs/lighthouse/seo/hreflang/).

Document has a valid `hreflang`

If a page doesn't specify a `lang` attribute, a screen reader assumes that the page is in the default language that the user chose when setting up the screen reader. If the page isn't actually in the default language, then the screen reader might not announce the page's text correctly. [Learn more about the `lang` attribute](https://dequeuniversity.com/rules/axe/4.7/html-has-lang).

`<html>` element has a `[lang]` attribute

Specifying a valid [BCP 47 language](https://www.w3.org/International/questions/qa-choosing-language-tags#question) helps screen readers announce text properly. [Learn how to use the `lang` attribute](https://dequeuniversity.com/rules/axe/4.7/html-lang-valid).

`<html>` element has a valid value for its `[lang]` attribute

Pages with unsuccessful HTTP status codes may not be indexed properly. [Learn more about HTTP status codes](https://developer.chrome.com/docs/lighthouse/seo/http-status-code/).

Page has successful HTTP status code

Informative elements should aim for short, descriptive alternate text. Decorative elements can be ignored with an empty alt attribute. [Learn more about the `alt` attribute](https://dequeuniversity.com/rules/axe/4.7/image-alt).

Image elements have `[alt]` attributes

Image display dimensions should match natural aspect ratio. [Learn more about image aspect ratio](https://developer.chrome.com/docs/lighthouse/best-practices/image-aspect-ratio/).

Displays images with incorrect aspect ratio

Informative elements should aim for short, descriptive alternative text. Alternative text that is exactly the same as the text adjacent to the link or image is potentially confusing for screen reader users, because the text will be read twice. [Learn more about the `alt` attribute](https://dequeuniversity.com/rules/axe/4.7/image-redundant-alt).

Image elements do not have `[alt]` attributes that are redundant text.

Image natural dimensions should be proportional to the display size and the pixel ratio to maximize image clarity. [Learn how to provide responsive images](https://web.dev/serve-responsive-images/).

Serves images with appropriate resolution

Issues logged to the `Issues` panel in Chrome Devtools indicate unresolved problems. They can come from network request failures, insufficient security controls, and other browser concerns. Open up the Issues panel in Chrome DevTools for more details on each issue.

Issues were logged in the `Issues` panel in Chrome Devtools

Service worker is the technology that enables your app to use many Progressive Web App features, such as offline, add to homescreen, and push notifications. With proper service worker and manifest implementations, browsers can proactively prompt users to add your app to their homescreen, which can lead to higher engagement. [Learn more about manifest installability requirements](https://developer.chrome.com/docs/lighthouse/pwa/installable-manifest/).

Web app manifest or service worker do not meet the installability requirements

Search engines are unable to include your pages in search results if they don't have permission to crawl them. [Learn more about crawler directives](https://developer.chrome.com/docs/lighthouse/seo/is-crawlable/).

Page isn’t blocked from indexing

All sites should be protected with HTTPS, even ones that don't handle sensitive data. This includes avoiding [mixed content](https://developers.google.com/web/fundamentals/security/prevent-mixed-content/what-is-mixed-content), where some resources are loaded over HTTP despite the initial request being served over HTTPS. HTTPS prevents intruders from tampering with or passively listening in on the communications between your app and your users, and is a prerequisite for HTTP/2 and many new web platform APIs. [Learn more about HTTPS](https://developer.chrome.com/docs/lighthouse/pwa/is-on-https/).

Uses HTTPS

Largest Contentful Paint marks the time at which the largest text or image is painted. [Learn more about the Largest Contentful Paint metric](https://developer.chrome.com/docs/lighthouse/performance/lighthouse-largest-contentful-paint/)

Largest Contentful Paint

Link text (and alternate text for images, when used as links) that is discernible, unique, and focusable improves the navigation experience for screen reader users. [Learn how to make links accessible](https://dequeuniversity.com/rules/axe/4.7/link-name).

Links do not have a discernible name

Descriptive link text helps search engines understand your content. [Learn how to make links more accessible](https://developer.chrome.com/docs/lighthouse/seo/link-text/).

Links have descriptive text

Screen readers have a specific way of announcing lists. Ensuring proper list structure aids screen reader output. [Learn more about proper list structure](https://dequeuniversity.com/rules/axe/4.7/list).

Lists contain only `<li>` elements and script supporting elements (`<script>` and `<template>`).

Screen readers require list items (`<li>`) to be contained within a parent `<ul>`, `<ol>` or `<menu>` to be announced properly. [Learn more about proper list structure](https://dequeuniversity.com/rules/axe/4.7/listitem).

List items (`<li>`) are contained within `<ul>`, `<ol>` or `<menu>` parent elements

A maskable icon ensures that the image fills the entire shape without being letterboxed when installing the app on a device. [Learn about maskable manifest icons](https://developer.chrome.com/docs/lighthouse/pwa/maskable-icon-audit/).

Manifest doesn't have a maskable icon

Meta descriptions may be included in search results to concisely summarize page content. [Learn more about the meta description](https://developer.chrome.com/docs/lighthouse/seo/meta-description/).

Document has a meta description

Disabling zooming is problematic for users with low vision who rely on screen magnification to properly see the contents of a web page. [Learn more about the viewport meta tag](https://dequeuniversity.com/rules/axe/4.7/meta-viewport).

`[user-scalable="no"]` is not used in the `<meta name="viewport">` element and the `[maximum-scale]` attribute is not less than 5.

The `unload` event does not fire reliably and listening for it can prevent browser optimizations like the Back-Forward Cache. Use `pagehide` or `visibilitychange` events instead. [Learn more about unload event listeners](https://web.dev/bfcache/#never-use-the-unload-event)

Avoids `unload` event listeners

Users are mistrustful of or confused by sites that request to send notifications without context. Consider tying the request to user gestures instead. [Learn more about responsibly getting permission for notifications](https://developer.chrome.com/docs/lighthouse/best-practices/notification-on-start/).

Avoids requesting the notification permission on page load

Preventing input pasting is a bad practice for the UX, and weakens security by blocking password managers.[Learn more about user-friendly input fields](https://developer.chrome.com/docs/lighthouse/best-practices/paste-preventing-inputs/).

Allows users to paste into input fields

Search engines can't index plugin content, and many devices restrict plugins or don't support them. [Learn more about avoiding plugins](https://developer.chrome.com/docs/lighthouse/seo/plugins/).

Document avoids plugins

Speed Index shows how quickly the contents of a page are visibly populated. [Learn more about the Speed Index metric](https://developer.chrome.com/docs/lighthouse/performance/speed-index/).

Speed Index

A themed splash screen ensures a high-quality experience when users launch your app from their homescreens. [Learn more about splash screens](https://developer.chrome.com/docs/lighthouse/pwa/splash-screen/).

Is not configured for a custom splash screen

A value greater than 0 implies an explicit navigation ordering. Although technically valid, this often creates frustrating experiences for users who rely on assistive technologies. [Learn more about the `tabindex` attribute](https://dequeuniversity.com/rules/axe/4.7/tabindex).

No element has a `[tabindex]` value greater than 0

The browser address bar can be themed to match your site. [Learn more about theming the address bar](https://developer.chrome.com/docs/lighthouse/pwa/themed-omnibox/).

Does not set a theme color for the address bar.

Sum of all time periods between FCP and Time to Interactive, when task length exceeded 50ms, expressed in milliseconds. [Learn more about the Total Blocking Time metric](https://developer.chrome.com/docs/lighthouse/performance/lighthouse-total-blocking-time/).

Total Blocking Time

A `<meta name="viewport">` not only optimizes your app for mobile screen sizes, but also prevents [a 300 millisecond delay to user input](https://developer.chrome.com/blog/300ms-tap-delay-gone-away/). [Learn more about using the viewport meta tag](https://developer.chrome.com/docs/lighthouse/pwa/viewport/).

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