First Contentful Paint

First Contentful Paint marks the time at which the first text or image is painted.

Speed Index

Speed Index shows how quickly the contents of a page are visibly populated.

Largest Contentful Paint

Largest Contentful Paint marks the time at which the largest text or image is painted.

Time to Interactive

Time to interactive is the amount of time it takes for the page to become fully interactive.

Total Blocking Time

Sum of all time periods between FCP and Time to Interactive, when task length exceeded 50ms, expressed in milliseconds.

Cumulative Layout Shift

Cumulative Layout Shift measures the movement of visible elements within the viewport.

Max Potential First Input Delay

The maximum potential First Input Delay that your users could experience is the duration of the longest task.

First Meaningful Paint

First Meaningful Paint measures when the primary content of a page is visible.

Eliminate render-blocking resources

Resources are blocking the first paint of your page. Consider delivering critical JS/CSS inline and deferring all non-critical JS/styles.

Properly size images

Serve images that are appropriately-sized to save cellular data and improve load time.

Defer offscreen images

Consider lazy-loading offscreen and hidden images after all critical resources have finished loading to lower time to interactive.

Minify CSS

Minifying CSS files can reduce network payload sizes.

Minify JavaScript

Minifying JavaScript files can reduce payload sizes and script parse time.

Reduce unused CSS

Reduce unused rules from stylesheets and defer CSS not used for above-the-fold content to decrease bytes consumed by network activity.

Reduce unused JavaScript

Reduce unused JavaScript and defer loading scripts until they are required to decrease bytes consumed by network activity.

Efficiently encode images

Optimized images load faster and consume less cellular data.

Serve images in next-gen formats

Image formats like WebP and AVIF often provide better compression than PNG or JPEG, which means faster downloads and less data consumption.

Enable text compression

Text-based resources should be served with compression (gzip, deflate or brotli) to minimize total network bytes.

Preconnect to required origins

Consider adding `preconnect` or `dns-prefetch` resource hints to establish early connections to important third-party origins.

Initial server response time was short

Keep the server response time for the main document short because all other requests depend on it.

Avoid multiple page redirects

Redirects introduce additional delays before the page can be loaded.

Preload key requests

Consider using `<link rel=preload>` to prioritize fetching resources that are currently requested later in page load.

Use HTTP/2

HTTP/2 offers many benefits over HTTP/1.1, including binary headers and multiplexing.

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.

Remove duplicate modules in JavaScript bundles

Remove large, duplicate JavaScript modules from bundles to reduce unnecessary bytes consumed by network activity.

Avoid serving legacy JavaScript to modern browsers

Polyfills and transforms enable legacy browsers to use new JavaScript features. However, many aren't necessary for modern browsers. For your bundled JavaScript, adopt a modern script deployment strategy using module/nomodule feature detection to reduce the amount of code shipped to modern browsers, while retaining support for legacy browsers. [Learn More](https://philipwalton.com/articles/deploying-es2015-code-in-production-today/)

Preload Largest Contentful Paint image

Preload the image used by the LCP element in order to improve your LCP time.

Avoids enormous network payloads

Large network payloads cost users real money and are highly correlated with long load times.

Uses efficient cache policy on static assets

A long cache lifetime can speed up repeat visits to your page.

Avoids an excessive DOM size

A large DOM will increase memory usage, cause longer [style calculations](https://developers.google.com/web/fundamentals/performance/rendering/reduce-the-scope-and-complexity-of-style-calculations), and produce costly [layout reflows](https://developers.google.com/speed/articles/reflow).

Avoid chaining critical requests

The Critical Request Chains below show you what resources are loaded with a high priority. Consider reducing the length of chains, reducing the download size of resources, or deferring the download of unnecessary resources to improve page load.

User Timing marks and measures

Consider instrumenting your app with the User Timing API to measure your app's real-world performance during key user experiences.

JavaScript execution time

Consider reducing the time spent parsing, compiling, and executing JS. You may find delivering smaller JS payloads helps with this.

Minimizes main-thread work

Consider reducing the time spent parsing, compiling and executing JS. You may find delivering smaller JS payloads helps with this.

All text remains visible during webfont loads

Leverage the font-display CSS feature to ensure text is user-visible while webfonts are loading.

Performance budget

Keep the quantity and size of network requests under the targets set by the provided performance budget.

Timing budget

Set a timing budget to help you keep an eye on the performance of your site. Performant sites load fast and respond to user input events quickly.

Keep request counts low and transfer sizes small

To set budgets for the quantity and size of page resources, add a budget.json file.

Minimize third-party usage

Third-party code can significantly impact load performance. Limit the number of redundant third-party providers and try to load third-party code after your page has primarily finished loading.

Lazy load third-party resources with facades

Some third-party embeds can be lazy loaded. Consider replacing them with a facade until they are required.

Largest Contentful Paint element

This is the largest contentful element painted within the viewport. [Learn More](https://web.dev/lighthouse-largest-contentful-paint/)

Avoid large layout shifts

These DOM elements contribute most to the CLS of the page.

Uses passive listeners to improve scrolling performance

Consider marking your touch and wheel event listeners as `passive` to improve your page's scroll performance.

Avoids `document.write()`

For users on slow connections, external scripts dynamically injected via `document.write()` can delay page load by tens of seconds.

Avoid long main-thread tasks

Lists the longest tasks on the main thread, useful for identifying worst contributors to input delay.

Avoid non-composited animations

Animations which are not composited can be janky and increase CLS.

Image elements have explicit `width` and `height`

Set an explicit width and height on image elements to reduce layout shifts and improve CLS.

Network Requests

Lists the network requests that were made during page load.

Network Round Trip Times

Network round trip times (RTT) have a large impact on performance. If the RTT to an origin is high, it's an indication that servers closer to the user could improve performance.

Server Backend Latencies

Server latencies can impact web performance. If the server latency of an origin is high, it's an indication the server is overloaded or has poor backend performance.

Tasks

Lists the toplevel main thread tasks that executed during page load.

Diagnostics

Collection of useful page vitals.

Metrics

Collects all available metrics.

Screenshot Thumbnails

This is what the load of your site looked like.

Final Screenshot

The last screenshot captured of the pageload.

Script Treemap Data

Used for treemap app

`[accesskey]` values are unique

Access keys let users quickly focus a part of the page. For proper navigation, each access key must be unique.

`[aria-*]` attributes match their roles

Each ARIA `role` supports a specific subset of `aria-*` attributes. Mismatching these invalidates the `aria-*` attributes.

`button`, `link`, and `menuitem` elements have accessible names

When an element doesn't have an accessible name, screen readers announce it with a generic name, making it unusable for users who rely on screen readers.

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

Assistive technologies, like screen readers, work inconsistently when `aria-hidden="true"` is set on the document `<body>`.

`[aria-hidden="true"]` elements do not contain focusable descendents

Focusable descendents within an `[aria-hidden="true"]` element prevent those interactive elements from being available to users of assistive technologies like screen readers.

ARIA input fields have accessible names

When an input field doesn't have an accessible name, screen readers announce it with a generic name, making it unusable for users who rely on screen readers.

ARIA `meter` elements have accessible names

When an element doesn't have an accessible name, screen readers announce it with a generic name, making it unusable for users who rely on screen readers.

ARIA `progressbar` elements have accessible names

When a `progressbar` element doesn't have an accessible name, screen readers announce it with a generic name, making it unusable for users who rely on screen readers.

`[role]`s have all required `[aria-*]` attributes

Some ARIA roles have required attributes that describe the state of the element to screen readers.

Elements with an ARIA `[role]` that require children to contain a specific `[role]` have all required children.

Some ARIA parent roles must contain specific child roles to perform their intended accessibility functions.

`[role]`s are contained by their required parent element

Some ARIA child roles must be contained by specific parent roles to properly perform their intended accessibility functions.

`[role]` values are valid

ARIA roles must have valid values in order to perform their intended accessibility functions.

ARIA toggle fields have accessible names

When a toggle field doesn't have an accessible name, screen readers announce it with a generic name, making it unusable for users who rely on screen readers.

ARIA `tooltip` elements have accessible names

When an element doesn't have an accessible name, screen readers announce it with a generic name, making it unusable for users who rely on screen readers.

ARIA `treeitem` elements have accessible names

When an element doesn't have an accessible name, screen readers announce it with a generic name, making it unusable for users who rely on screen readers.

`[aria-*]` attributes have valid values

Assistive technologies, like screen readers, can't interpret ARIA attributes with invalid values.

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

Assistive technologies, like screen readers, can't interpret ARIA attributes with invalid names.

Buttons have an accessible name

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.

The page contains a heading, skip link, or landmark region

Adding ways to bypass repetitive content lets keyboard users navigate the page more efficiently.

Background and foreground colors have a sufficient contrast ratio

Low-contrast text is difficult or impossible for many users to read.

`<dl>`'s contain only properly-ordered `<dt>` and `<dd>` groups, `<script>`, `<template>` or `<div>` elements.

When definition lists are not properly marked up, screen readers may produce confusing or inaccurate output.

Definition list items are wrapped in `<dl>` elements

Definition list items (`<dt>` and `<dd>`) must be wrapped in a parent `<dl>` element to ensure that screen readers can properly announce them.

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.

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

All focusable elements must have a unique `id` to ensure that they're visible to assistive technologies.

ARIA IDs are unique

The value of an ARIA ID must be unique to prevent other instances from being overlooked by assistive technologies.

No form fields have multiple labels

Form fields with multiple labels can be confusingly announced by assistive technologies like screen readers which use either the first, the last, or all of the labels.

`<frame>` or `<iframe>` elements have a title

Screen reader users rely on frame titles to describe the contents of frames.

Heading elements appear in a sequentially-descending order

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.

`<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.

`<html>` element has a valid value for its `[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.

Image elements have `[alt]` attributes

Informative elements should aim for short, descriptive alternate text. Decorative elements can be ignored with an empty alt attribute.

`<input type="image">` elements have `[alt]` text

When an image is being used as an `<input>` button, providing alternative text can help screen reader users understand the purpose of the button.

Form elements have associated labels

Labels ensure that form controls are announced properly by assistive technologies, like screen readers.

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.

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.

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.

The document does not use `<meta http-equiv="refresh">`

Users do not expect a page to refresh automatically, and doing so will move focus back to the top of the page. This may create a frustrating or confusing experience.

`[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.

`<object>` elements have `[alt]` text

Screen readers cannot translate non-text content. Adding alt text to `<object>` elements helps screen readers convey meaning to users.

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

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.

Cells in a `<table>` element that use the `[headers]` attribute refer to table cells within the same table.

Screen readers have features to make navigating tables easier. Ensuring `<td>` cells using the `[headers]` attribute only refer to other cells in the same table may improve the experience for screen reader users.