first-contentful-paint | performance | First Contentful Paint marks the time at which the first text or image is painted. Learn more. | 10 | First Contentful Paint | FCP | millisecond |
speed-index | performance | Speed Index shows how quickly the contents of a page are visibly populated. Learn more. | 10 | Speed Index | SI | millisecond |
largest-contentful-paint | performance | Largest Contentful Paint marks the time at which the largest text or image is painted. Learn more | 25 | Largest Contentful Paint | LCP | millisecond |
interactive | performance | Time to interactive is the amount of time it takes for the page to become fully interactive. Learn more. | 10 | Time to Interactive | TTI | millisecond |
total-blocking-time | performance | Sum of all time periods between FCP and Time to Interactive, when task length exceeded 50ms, expressed in milliseconds. Learn more. | 30 | Total Blocking Time | TBT | millisecond |
cumulative-layout-shift | performance | Cumulative Layout Shift measures the movement of visible elements within the viewport. Learn more. | 15 | Cumulative Layout Shift | CLS | unitless |
aria-allowed-attr | accessibility | Each ARIA role supports a specific subset of aria-* attributes. Mismatching these invalidates the aria-* attributes. Learn more. | 10 | [aria-*] attributes match their roles | | |
aria-hidden-body | accessibility | Assistive technologies, like screen readers, work inconsistently when aria-hidden="true" is set on the document <body>. Learn more. | 10 | [aria-hidden="true"] is not present on the document <body> | | |
aria-hidden-focus | accessibility | Focusable descendents within an [aria-hidden="true"] element prevent those interactive elements from being available to users of assistive technologies like screen readers. Learn more. | 3 | [aria-hidden="true"] elements do not contain focusable descendents | | |
aria-valid-attr-value | accessibility | Assistive technologies, like screen readers, can't interpret ARIA attributes with invalid values. Learn more. | 10 | [aria-*] attributes have valid values | | |
aria-valid-attr | accessibility | Assistive technologies, like screen readers, can't interpret ARIA attributes with invalid names. Learn more. | 10 | [aria-*] attributes are valid and not misspelled | | |
button-name | accessibility | When a button doesn't have an accessible name, screen readers announce it as "button", making it unusable for users who rely on screen readers. Learn more. | 10 | Buttons do not have an accessible name | | |
bypass | accessibility | Adding ways to bypass repetitive content lets keyboard users navigate the page more efficiently. Learn more. | 3 | The page contains a heading, skip link, or landmark region | | |
color-contrast | accessibility | Low-contrast text is difficult or impossible for many users to read. Learn more. | 3 | Background and foreground colors do not have a sufficient contrast ratio. | | |
document-title | accessibility | 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. | 3 | Document has a <title> element | | |
duplicate-id-active | accessibility | All focusable elements must have a unique id to ensure that they're visible to assistive technologies. Learn more. | 3 | [id] attributes on active, focusable elements are unique | | |
duplicate-id-aria | accessibility | The value of an ARIA ID must be unique to prevent other instances from being overlooked by assistive technologies. Learn more. | 10 | ARIA IDs are not unique | | |
heading-order | accessibility | 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. | 2 | Heading elements are not in a sequentially-descending order | | |
html-has-lang | accessibility | 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. | 3 | <html> element does not have a [lang] attribute | | |
image-alt | accessibility | Informative elements should aim for short, descriptive alternate text. Decorative elements can be ignored with an empty alt attribute. Learn more. | 10 | Image elements have [alt] attributes | | |
label | accessibility | Labels ensure that form controls are announced properly by assistive technologies, like screen readers. Learn more. | 10 | Form elements have associated labels | | |
link-name | accessibility | 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 more. | 3 | Links do not have a discernible name | | |
list | accessibility | Screen readers have a specific way of announcing lists. Ensuring proper list structure aids screen reader output. Learn more. | 3 | Lists do not contain only <li> elements and script supporting elements (<script> and <template>). | | |
listitem | accessibility | Screen readers require list items (<li>) to be contained within a parent <ul> or <ol> to be announced properly. Learn more. | 3 | List items (<li>) are contained within <ul> or <ol> parent elements | | |
meta-viewport | accessibility | 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. | 10 | [user-scalable="no"] is used in the <meta name="viewport"> element or the [maximum-scale] attribute is less than 5. | | |
tabindex | accessibility | 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. | 3 | No element has a [tabindex] value greater than 0 | | |
is-on-https | best-practices | All sites should be protected with HTTPS, even ones that don't handle sensitive data. This includes avoiding 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. | 1 | Uses HTTPS | | |
external-anchors-use-rel-noopener | best-practices | Add rel="noopener" or rel="noreferrer" to any external links to improve performance and prevent security vulnerabilities. Learn more. | 1 | Links to cross-origin destinations are unsafe | | |
geolocation-on-start | best-practices | 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. | 1 | Avoids requesting the geolocation permission on page load | | |
notification-on-start | best-practices | 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. | 1 | Avoids requesting the notification permission on page load | | |
no-vulnerable-libraries | best-practices | Some third-party scripts may contain known security vulnerabilities that are easily identified and exploited by attackers. Learn more. | 1 | Includes front-end JavaScript libraries with known security vulnerabilities | | |
password-inputs-can-be-pasted-into | best-practices | Preventing password pasting undermines good security policy. Learn more. | 1 | Allows users to paste into password fields | | |
image-aspect-ratio | best-practices | Image display dimensions should match natural aspect ratio. Learn more. | 1 | Displays images with correct aspect ratio | | |
image-size-responsive | best-practices | Image natural dimensions should be proportional to the display size and the pixel ratio to maximize image clarity. Learn more. | 1 | Serves images with appropriate resolution | | |
doctype | best-practices | Specifying a doctype prevents the browser from switching to quirks-mode. Learn more. | 1 | Page has the HTML doctype | | |
charset | best-practices | 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. | 1 | Properly defines charset | | |
no-unload-listeners | best-practices | The unload event does not fire reliably and listening for it can prevent browser optimizations like the Back-Forward Cache. Consider using the pagehide or visibilitychange events instead. Learn more | 1 | Avoids unload event listeners | | |
appcache-manifest | best-practices | Application Cache is deprecated. Learn more. | 1 | Avoids Application Cache | | |
deprecations | best-practices | Deprecated APIs will eventually be removed from the browser. Learn more. | 1 | Avoids deprecated APIs | | |
errors-in-console | best-practices | Errors logged to the console indicate unresolved problems. They can come from network request failures and other browser concerns. Learn more | 1 | No browser errors logged to the console | | |
inspector-issues | best-practices | 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. | 1 | No issues in the Issues panel in Chrome Devtools | | |
viewport | seo | Add a <meta name="viewport"> tag to optimize your app for mobile screens. Learn more. | 1 | Has a <meta name="viewport"> tag with width or initial-scale | | |
document-title | seo | 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. | 1 | Document has a <title> element | | |
meta-description | seo | Meta descriptions may be included in search results to concisely summarize page content. Learn more. | 1 | Document has a meta description | | |
http-status-code | seo | Pages with unsuccessful HTTP status codes may not be indexed properly. Learn more. | 1 | Page has successful HTTP status code | | |
link-text | seo | Descriptive link text helps search engines understand your content. Learn more. | 1 | Links have descriptive text | | |
crawlable-anchors | seo | 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 More | 1 | Links are crawlable | | |
is-crawlable | seo | Search engines are unable to include your pages in search results if they don't have permission to crawl them. Learn more. | 1 | Page isn’t blocked from indexing | | |
robots-txt | seo | If your robots.txt file is malformed, crawlers may not be able to understand how you want your website to be crawled or indexed. Learn more. | 1 | robots.txt is valid | | |
image-alt | seo | Informative elements should aim for short, descriptive alternate text. Decorative elements can be ignored with an empty alt attribute. Learn more. | 1 | Image elements have [alt] attributes | | |
hreflang | seo | hreflang links tell search engines what version of a page they should list in search results for a given language or region. Learn more. | 1 | Document has a valid hreflang | | |
plugins | seo | Search engines can't index plugin content, and many devices restrict plugins or don't support them. Learn more. | 1 | Document avoids plugins | | |
first_contentful_paint_ms | performance_google | First Contentful Paint (FCP) is an important, user-centric metric for measuring perceived load speed because it marks the first point in the page load timeline where the user can see anything on the screen—a fast FCP helps reassure the user that something is happening. Learn more. | | First Contentfull Paint (FCP) | | millisecond |
first_input_delay_ms | performance_google | First Input Delay (FID) is an important, user-centric metric for measuring load responsiveness because it quantifies the experience users feel when trying to interact with unresponsive pages—a low FID helps ensure that the page is usable. Learn more. | | First Input Delay (FID) | | millisecond |
largest_contentful_paint_ms | performance_google | Largest Contentful Paint (LCP) is an important, user-centric metric for measuring perceived load speed because it marks the point in the page load timeline when the page's main content has likely loaded—a fast LCP helps reassure the user that the page is useful. Learn more. | | Largest Contentful Paint (LCP) | | millisecond |
cumulative_layout_shift_score | performance_google | Cumulative Layout Shift (CLS) is an important, user-centric metric for measuring visual stability because it helps quantify how often users experience unexpected layout shifts—a low CLS helps ensure that the page is delightful. Learn more. | | Cumulative Layout Shift (CLS) | | score |
experimental_time_to_first_byte | performance_google | Time to First Byte (TTFB) is a foundational metric for measuring connection setup time and web server responsiveness in both the lab and the field. It helps identify when a web server is too slow to respond to requests. In the case of navigation requests—that is, requests for an HTML document—it precedes every other meaningful loading performance metric. Learn more. | | Time to First Byte (TTFB) | | score |
experimental_interaction_to_next_paint | performance_google | Interaction to Next Paint (INP) is an experimental metric that assesses responsiveness. INP observes the latency of all interactions a user has made with the page, and reports a single value which all (or nearly all) interactions were below. A low INP means the page was consistently able to respond quickly to all—or the vast majority—of user interactions. Learn more. | | Interaction to Next Paint (INP) | | score |