Max Potential FID
The potential First Input Delay that your users could experience is the duration, in milliseconds, of the longest task.
Properly size images
Serve images that are appropriately-sized to save cellular data and improve load time. Learn more.
Minify CSS
Minifying CSS files can reduce network payload sizes. Learn more.
Minify JavaScript
Minifying JavaScript files can reduce payload sizes and script parse time. Learn more.
Remove unused CSS
Remove unused rules from stylesheets to reduce unnecessary bytes consumed by network activity. Learn more.
Efficiently encode images
Optimized images load faster and consume less cellular data. Learn more.
Enable text compression
Text-based resources should be served with compression (gzip, deflate or brotli) to minimize total network bytes. Learn more.
Server response times are low (TTFB)
Time To First Byte identifies the time at which your server sends a response. Learn more.
Preload key requests
Consider using to prioritize fetching resources that are currently requested later in page load. Learn more.
Use video formats for animated content
Large GIFs are inefficient for delivering animated content. Consider using MPEG4/WebM videos for animations and PNG/WebP for static images instead of GIF to save network bytes. Learn more
Avoids enormous network payloads
Large network payloads cost users real money and are highly correlated with long load times. Learn more.
Uses efficient cache policy on static assets
A long cache lifetime can speed up repeat visits to your page. Learn more.
Avoids an excessive DOM size
A large DOM can increase memory usage, cause longer style calculations, and produce costly layout reflows. Learn more.
JavaScript execution time
Consider reducing the time spent parsing, compiling, and executing JS. You may find delivering smaller JS payloads helps with this. Learn more.
Minimizes main-thread work
Consider reducing the time spent parsing, compiling and executing JS. You may find delivering smaller JS payloads helps with this.
Avoids Application Cache
Application Cache is deprecated. Learn more.
Uses HTTPS
All sites should be protected with HTTPS, even ones that don't handle sensitive data. 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.
Uses HTTP/2 for its own resources
HTTP/2 offers many benefits over HTTP/1.1, including binary headers, multiplexing, and server push. Learn more.
Uses passive listeners to improve scrolling performance
Consider marking your touch and wheel event listeners as passive to improve your page's scroll performance. Learn more.
Avoids document.write()
For users on slow connections, external scripts dynamically injected via document.write() can delay page load by tens of seconds. Learn more.
Links to cross-origin destinations are safe
Add rel="noopener" or rel="noreferrer" to any external links to improve performance and prevent security vulnerabilities. Learn more.
Avoids requesting the geolocation permission on page load
Users are mistrustful of or confused by sites that request their location without context. Consider tying the request to user gestures instead. Learn more.
Page has the HTML doctype
Specifying a doctype prevents the browser from switching to quirks-mode. Read more on the MDN Web Docs page
Avoids front-end JavaScript libraries with known security vulnerabilities
Some third-party scripts may contain known security vulnerabilities that are easily identified and exploited by attackers. Learn more.
Detected JavaScript libraries
All front-end JavaScript libraries detected on the page.
Avoids requesting the notification permission on page load
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.
Avoids deprecated APIs
Deprecated APIs will eventually be removed from the browser. Learn more.
Allows users to paste into password fields
Preventing password pasting undermines good security policy. Learn more.
No browser errors logged to the console
Errors logged to the console indicate unresolved problems. They can come from network request failures and other browser concerns.
Displays images with correct aspect ratio
Image display dimensions should match natural aspect ratio. Learn more.
Has a <meta name="viewport"> tag with width or initial-scale
Add a viewport meta tag to optimize your app for mobile screens. Learn more.
Document has a meta description
Meta descriptions may be included in search results to concisely summarize page content. Learn more.
Page has successful HTTP status code
Pages with unsuccessful HTTP status codes may not be indexed properly. Learn more.
Links have descriptive text
Descriptive link text helps search engines understand your content. Learn more.
Page isn’t blocked from indexing
Search engines are unable to include your pages in search results if they don't have permission to crawl them. Learn more.
Document has a valid hreflang
hreflang links tell search engines what version of a page they should list in search results for a given language or region. Learn more.
Document uses legible font sizes
Font sizes less than 12px are too small to be legible and require mobile visitors to “pinch to zoom” in order to read. Strive to have >60% of page text ≥12px. Learn more.
Document avoids plugins
Search engines can't index plugin content, and many devices restrict plugins or don't support them. Learn more.
Tap targets are sized appropriately
Interactive elements like buttons and links should be large enough (48x48px), and have enough space around them, to be easy enough to tap without overlapping onto other elements. Learn more.
The page contains a heading, skip link, or landmark region
Adding ways to bypass repetitive content lets keyboard users navigate the page more efficiently. Learn more.
Background and foreground colors have a sufficient contrast ratio
Low-contrast text is difficult or impossible for many users to read. Learn more.
Document has a <title> element
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.
[id] attributes on the page are unique
The value of an id attribute must be unique to prevent other instances from being overlooked by assistive technologies. Learn more.
<html> element has a [lang] attribute
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.
<html> element has a valid value for its [lang] attribute
Specifying a valid BCP 47 language helps screen readers announce text properly. Learn more.
Links have a discernible name
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.
Lists contain only <li> elements and script supporting elements (<script> and <template>).
Screen readers have a specific way of announcing lists. Ensuring proper list structure aids screen reader output. Learn more.
List items (<li>) are contained within <ul> or <ol> parent elements
Screen readers require list items (<li>) to be contained within a parent <ul> or <ol> to be announced properly. Learn more.
[user-scalable="no"] is not used in the <meta name="viewport"> element and the [maximum-scale] attribute is not less than 5.
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.
Current page responds with a 200 when offline
If you're building a Progressive Web App, consider using a service worker so that your app can work offline. Learn more.
Redirects HTTP traffic to HTTPS
If you've already set up HTTPS, make sure that you redirect all HTTP traffic to HTTPS. Learn more.
Content is sized correctly for the viewport
If the width of your app's content doesn't match the width of the viewport, your app might not be optimized for mobile screens. Learn more.
Contains some content when JavaScript is not available
Your app should display some content when JavaScript is disabled, even if it's just a warning to the user that JavaScript is required to use the app. Learn more.