Lighthouse Desktop

· 0 checks — Desktop Lighthouse audit -- Performance, Accessibility, Best Practices, and SEO category breakdown.

SCORE

GRADE

FIX

REVIEW

PASS

INFO

Detailed Report

Audit breakdown by category with detailed findings.

Performance

Insights

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

Why this matters

Performance issues directly impact user engagement and conversion rates.

Polyfills and transforms enable older browsers to use new JavaScript features. However, many aren't necessary for modern browsers. Consider modifying your JavaScript build process to not transpile Baseline features, unless you know you must support older browsers. Learn why most sites can deploy ES6+ code without transpiling

Why this matters

Performance issues directly impact user engagement and conversion rates.

3rd party code can significantly impact load performance. Reduce and defer loading of 3rd party code to prioritize your page's content.

Why this matters

Performance issues directly impact user engagement and conversion rates.

Your first network request is the most important. Reduce its latency by avoiding redirects, ensuring a fast server response, and enabling text compression.

Why this matters

Performance issues directly impact user engagement and conversion rates.

A forced reflow occurs when JavaScript queries geometric properties (such as offsetWidth) after styles have been invalidated by a change to the DOM state. This can result in poor performance. Learn more about forced reflows and possible mitigations.

Why this matters

Performance issues directly impact user engagement and conversion rates.

headings: [map[key:source label:Source valueType:source-location] map[granularity:1 key:reflowTime label:Total reflow time valueType:ms]]

items: [map[reflowTime:4.519 source:map[type:text value:[unattributed]]] map[reflowTime:21.121 source:map[column:91010 line:1 type:source-location url:https://www.britishmuseum.org/sites/default/files/js/js_u3kNJ_Z2LZHlpL78jbhLsQ8GatG5vHJjaeoQR8pPIOk.js?scope=footer&delta=4&language=en&theme=numiko&include=eJzLK83NzM7XT8_JT0rM0S1OLsosKCnWycMmqpuRmpiSWgQA9VcTkw urlProvider:network]] map[reflowTime:0.691 source:map[column:233587 line:1 type:source-location url:https://www.britishmuseum.org/sites/default/files/js/js_u3kNJ_Z2LZHlpL78jbhLsQ8GatG5vHJjaeoQR8pPIOk.js?scope=footer&delta=4&language=en&theme=numiko&include=eJzLK83NzM7XT8_JT0rM0S1OLsosKCnWycMmqpuRmpiSWgQA9VcTkw urlProvider:network]] map[reflowTime:5.741 source:map[column:261248 line:1 type:source-location url:https://www.britishmuseum.org/sites/default/files/js/js_u3kNJ_Z2LZHlpL78jbhLsQ8GatG5vHJjaeoQR8pPIOk.js?scope=footer&delta=4&language=en&theme=numiko&include=eJzLK83NzM7XT8_JT0rM0S1OLsosKCnWycMmqpuRmpiSWgQA9VcTkw urlProvider:network]] map[reflowTime:3.028 source:map[column:255685 line:1 type:source-location url:https://www.britishmuseum.org/sites/default/files/js/js_u3kNJ_Z2LZHlpL78jbhLsQ8GatG5vHJjaeoQR8pPIOk.js?scope=footer&delta=4&language=en&theme=numiko&include=eJzLK83NzM7XT8_JT0rM0S1OLsosKCnWycMmqpuRmpiSWgQA9VcTkw urlProvider:network]] map[reflowTime:2.017 source:map[column:267273 line:1 type:source-location url:https://www.britishmuseum.org/sites/default/files/js/js_u3kNJ_Z2LZHlpL78jbhLsQ8GatG5vHJjaeoQR8pPIOk.js?scope=footer&delta=4&language=en&theme=numiko&include=eJzLK83NzM7XT8_JT0rM0S1OLsosKCnWycMmqpuRmpiSWgQA9VcTkw urlProvider:network]]]

Reducing the download time of images can improve the perceived load time of the page and LCP. Learn more about optimizing image size

Why this matters

Performance issues directly impact user engagement and conversion rates.

	URL	Resource Size	Est Savings
A close up of a section of a feathered Hawai'ian cloak showing yellow and black… `div.teaser__image-container > div.media > picture > img`	/sites/default/files/styles/16_9_media_large/public/2025-...	246.8 KiB	214.6 KiB
Section of the Bayeux Tapestry showing a group of warriors with shields and spe… `div.teaser__image-container > div.media > picture > img`	/sites/default/files/styles/16_9_media_large/public/2026-...	218.5 KiB	186.2 KiB
A samurai helmet with gold-coloured horns and a metal face mask with a moustach… `div.teaser__image-container > div.media > picture > img`	/sites/default/files/styles/16_9_media_large/public/2025-...	103.9 KiB	82.3 KiB
A wide shot of the Great Court with the roof and Reading Room in view `div.hero__background > div.media > picture > img`	/sites/default/files/styles/uncropped_large/public/2019-1...	108.8 KiB	9.9 KiB

Optimize LCP by making the LCP image discoverable from the HTML immediately, and avoiding lazy-loading

Why this matters

Performance issues directly impact user engagement and conversion rates.

lhId: page-3-IMG

nodeLabel: A wide shot of the Great Court with the roof and Reading Room in view

path: 1,HTML,1,BODY,5,DIV,4,DIV,0,DIV,2,MAIN,0,DIV,0,DIV,0,DIV,0,DIV,0,PICTURE,5,IMG

selector: div.hero__background > div.media > picture > img

snippet: <img loading="eager" width="750" height="750" data-focal-position="center right" src="https://www.britishmuseum.org/sites/default/files/styles/uncropped_large/p…" alt="A wide shot of the Great Court with the roof and Reading Room in view">

Avoid chaining critical requests by reducing the length of chains, reducing the download size of resources, or deferring the download of unnecessary resources to improve page load.

Why this matters

Performance issues directly impact user engagement and conversion rates.

description: [preconnect](https://developer.chrome.com/docs/lighthouse/performance/uses-rel-preconnect/) hints help the browser establish a connection earlier in the page load, saving time when the first request for that origin is made. The following are the origins that the page preconnected to.

title: Preconnected origins

description: Add [preconnect](https://developer.chrome.com/docs/lighthouse/performance/uses-rel-preconnect/) hints to your most important origins, but try to use no more than 4.

title: Preconnect candidates

value: No additional origins are good candidates for preconnecting

Requests are blocking the page's initial render, which may delay LCP. Deferring or inlining can move these network requests out of the critical path.

Why this matters

Performance issues directly impact user engagement and conversion rates.

URL	Transfer Size	Duration
/sites/default/files/css/css_qv6dCFGN2Vda1nUS7_s-LrSxyqnB...	44.3 KiB	227 ms
/sites/default/files/js/js_SLwwA2J3XCQ_1HHbqjZARtcKpH5ptr...	1.3 KiB	147 ms
/sites/default/files/css/css_VsHlxZe888vVcIftkt15QWpKH3V1...	590 B	67 ms

A long cache lifetime can speed up repeat visits to your page. Learn more about caching.

Why this matters

Performance issues directly impact user engagement and conversion rates.

Request	Cache TTL	Transfer Size
consent.cookiebot.com/Framework/IAB/consent-sdk-2.3.js	98.0 s	87.9 KiB
consent.cookiebot.com/uc.js	612.0 s	35.7 KiB
/cdn-cgi/challenge-platform/h/b/scripts/jsd/0b8fb825cb67/...	14400.0 s	13.0 KiB
bmwebsitestreaming.blob.core.windows.net/bmvideo/Tour_of_the_British_Museum.mp4	0.0 ms	0 B

These insights are also available in the Chrome DevTools Performance Panel - record a trace to view more detailed information.

Redirects introduce additional delays before the page can be loaded. Learn how to avoid page redirects.

Why this matters

Performance issues directly impact user engagement and conversion rates.

Estimated savings: 247 ms

URL	Time Spent
britishmuseum.org/	247 ms
www.britishmuseum.org/	0.0 ms

The maximum potential First Input Delay that your users could experience is the duration of the longest task. Learn more about the Maximum Potential First Input Delay metric.

Why this matters

Performance issues directly impact user engagement and conversion rates.

Time to Interactive is the amount of time it takes for the page to become fully interactive. Learn more about the Time to Interactive metric.

Why this matters

Performance issues directly impact user engagement and conversion rates.

TTI

Diagnostics

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

Why this matters

Performance issues directly impact user engagement and conversion rates.

Estimated savings: 50 ms 37.8 KiB

URL	Transfer Size	Est Savings
/sites/default/files/css/css_qv6dCFGN2Vda1nUS7_s-LrSxyqnB...	43.8 KiB	37.8 KiB

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

Why this matters

Performance issues directly impact user engagement and conversion rates.

Estimated savings: 50 ms 594.6 KiB

URL	Transfer Size	Est Savings
/sites/default/files/js/js_u3kNJ_Z2LZHlpL78jbhLsQ8GatG5vH...	111.3 KiB	75.5 KiB
www.googletagmanager.com/gtm.js?id=GTM-MW5VCK	189.5 KiB	74.0 KiB
www.googletagmanager.com/gtag/destination?id=G-08TLB9R8X1&cx=c&gtm=4e64h1	173.9 KiB	66.0 KiB
consent.cookiebot.com/Framework/IAB/consent-sdk-2.3.js	87.7 KiB	64.2 KiB
www.googletagmanager.com/gtag/js?id=AW-967338294&cx=c&gtm=4e64h1	144.2 KiB	63.7 KiB
www.googletagmanager.com/gtag/js?id=AW-869763654&cx=c&gtm=4e64h1	144.2 KiB	63.7 KiB
www.googletagmanager.com/gtag/js?id=AW-944964254&cx=c&gtm=4e64h1	144.1 KiB	63.1 KiB
www.googletagmanager.com/gtag/js?id=DC-8361401&cx=c&gtm=4e64h1	130.0 KiB	61.1 KiB
consent.cookiebot.com/uc.js	35.5 KiB	22.2 KiB
/ec5f4b04-e699-4bea-a9de-eda95d4d9fb7/cc.js?renew=false&r...	297.4 KiB	21.1 KiB
www.britishmuseum.org/core/assets/vendor/jquery/jquery.min.js?v=4.0.0	31.4 KiB	20.0 KiB

Consider reducing the time spent parsing, compiling and executing JS. You may find delivering smaller JS payloads helps with this. Learn how to minimize main-thread work

Why this matters

Performance issues directly impact user engagement and conversion rates.

Category	Time Spent
Script Evaluation	1.3 s
Parse HTML & CSS	1.1 s
Other	414 ms
Style & Layout	174 ms
Script Parsing & Compilation	165 ms
Garbage Collection	52 ms
Rendering	36 ms

Minifying JavaScript files can reduce payload sizes and script parse time. Learn how to minify JavaScript.

Why this matters

Performance issues directly impact user engagement and conversion rates.

Estimated savings: 0.0 ms 5.6 KiB

URL	Transfer Size	Est Savings
www.britishmuseum.org/core/misc/drupal.js?v=11.3.7	7.1 KiB	5.6 KiB

Large network payloads cost users real money and are highly correlated with long load times. Learn how to reduce payload sizes.

Why this matters

Performance issues directly impact user engagement and conversion rates.

URL	Transfer Size
bmwebsitestreaming.blob.core.windows.net/bmvideo/Tour_of_the_British_Museum.mp4	1.2 MiB
/ec5f4b04-e699-4bea-a9de-eda95d4d9fb7/cc.js?renew=false&r...	297.7 KiB
/sites/default/files/styles/16_9_media_large/public/2025-...	247.3 KiB
/sites/default/files/styles/16_9_media_large/public/2026-...	219.0 KiB
www.googletagmanager.com/gtm.js?id=GTM-MW5VCK	189.9 KiB
www.googletagmanager.com/gtag/destination?id=G-08TLB9R8X1&cx=c&gtm=4e64h1	174.0 KiB
www.googletagmanager.com/gtag/js?id=AW-967338294&cx=c&gtm=4e64h1	144.2 KiB
www.googletagmanager.com/gtag/js?id=AW-869763654&cx=c&gtm=4e64h1	144.2 KiB
www.googletagmanager.com/gtag/js?id=AW-944964254&cx=c&gtm=4e64h1	144.2 KiB
www.googletagmanager.com/gtag/js?id=DC-8361401&cx=c&gtm=4e64h1	130.1 KiB

More information about the performance of your application. These numbers don't directly affect the Performance score.

●Layout shift culprits

●Optimize DOM size

●Font display

●LCP breakdown

●Modern HTTP

●Optimize viewport for mobile

●Minify CSS

●User Timing marks and measures 5 user timings

●JavaScript execution time 1.3 s

●Avoid long main-thread tasks 4 long tasks found

●Avoid non-composited animations 4 animated elements found

●Image elements have explicit `width` and `height`

●Page didn't prevent back/forward cache restoration

●Network Requests

●Network Round Trip Times 70 ms

●Server Backend Latencies 750 ms

●Tasks

●Diagnostics

●Metrics

●Screenshot Thumbnails

●Final Screenshot

●Script Treemap Data

●Resources Summary

●Initial server response time was short Root document took 30 ms

●Avoid large layout shifts 2 layout shifts found

○INP breakdown

Accessibility

These checks highlight opportunities to improve the accessibility of your web app. Automatic detection can only detect a subset of issues and does not guarantee the accessibility of your web app, so manual testing is also encouraged.

ARIA

Some ARIA parent roles must contain specific child roles to perform their intended accessibility functions. Learn more about roles and required children elements.

Why this matters

Performance issues directly impact user engagement and conversion rates.

Failing Elements
Consent Details Ad Settings About `div.ckb-modal-bgshade > div.ckb-modal > div.ckb-modal__tablist-wrapper > ul.ckb-tablist`

Some ARIA child roles must be contained by specific parent roles to properly perform their intended accessibility functions. Learn more about ARIA roles and required parent element.

Why this matters

Performance issues directly impact user engagement and conversion rates.

Failing Elements
Consent `div.ckb-modal__tablist-wrapper > ul.ckb-tablist > li.ckb-tablist__tab > button#ckb-tab-consent`
Details `div.ckb-modal__tablist-wrapper > ul.ckb-tablist > li.ckb-tablist__tab > button#ckb-tab-details`
Ad Settings `div.ckb-modal__tablist-wrapper > ul.ckb-tablist > li.ckb-tablist__tab > button#ckb-tab-adsettings`
About `div.ckb-modal__tablist-wrapper > ul.ckb-tablist > li.ckb-tablist__tab > button#ckb-tab-about`

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

Why this matters

Performance issues directly impact user engagement and conversion rates.

Failing Elements
The British Museum British Museum Consent Details Ad Settings About Responsible… `body#page-top > div#cookiebot`

ARIA dialog elements without accessible names may prevent screen readers users from discerning the purpose of these elements. Learn how to make ARIA dialog elements more accessible.

Why this matters

Informational: a Permissions-Policy directive showing feature -> allowed origins.

Source: MDN Permissions-Policy

Failing Elements
The British Museum British Museum Consent Details Ad Settings About Responsible… `body#page-top > div#cookiebot`

These are opportunities to improve the usage of ARIA in your application which may enhance the experience for users of assistive technology, like a screen reader.

Tables and lists

Screen readers have a specific way of announcing lists. Ensuring proper list structure aids screen reader output. Learn more about proper list structure.

Why this matters

Performance issues directly impact user engagement and conversion rates.

Failing Elements
Egypt Read more Desire, love and identity Read the blog Animals See the collect… `div.teaser-listing__container > div.carousel-container > div.carousel > ul#swiper-wrapper-decdf8befaab4a910`
Inspired by the Museum https://www.britishmuseumshoponline.org/inspired-by/insp… `div.teaser-listing__container > div.carousel-container > div.carousel > ul#swiper-wrapper-d6cbc6f8c43b6230`

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.

Why this matters

Performance issues directly impact user engagement and conversion rates.

Failing Elements
Consent `div.ckb-modal > div.ckb-modal__tablist-wrapper > ul.ckb-tablist > li.ckb-tablist__tab`
Details `div.ckb-modal > div.ckb-modal__tablist-wrapper > ul.ckb-tablist > li.ckb-tablist__tab`
Ad Settings `div.ckb-modal > div.ckb-modal__tablist-wrapper > ul.ckb-tablist > li.ckb-tablist__tab`
About `div.ckb-modal > div.ckb-modal__tablist-wrapper > ul.ckb-tablist > li.ckb-tablist__tab`

These are opportunities to improve the experience of reading tabular or list data using assistive technology, like a screen reader.

Visible text labels that do not match the accessible name can result in a confusing experience for screen reader users. Learn more about accessible names.

Why this matters

Performance issues directly impact user engagement and conversion rates.

Failing Elements
partners `div#ckb-content-consent > div.ckb-modal__text > p > a`
details section `div#ckb-content-consent > div.ckb-modal__text > p > a`

○Interactive controls are keyboard focusable

○Interactive elements indicate their purpose and state

○The page has a logical tab order

○Visual order on the page follows DOM order

○User focus is not accidentally trapped in a region

○The user's focus is directed to new content added to the page

○HTML5 landmark elements are used to improve navigation

○Offscreen content is hidden from assistive technology

○Custom controls have associated labels

○Custom controls have ARIA roles

●`[aria-*]` attributes match their roles

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

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

●`[role]` values are valid

●`[aria-*]` attributes have valid values

●Buttons have an accessible name

●Image elements have `[alt]` attributes

●Form elements have associated labels

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

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

●ARIA attributes are used as specified for the element's role

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

●Elements use only permitted ARIA attributes

●Background and foreground colors have a sufficient contrast ratio

●Document has a `<title>` element

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

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

●Links are distinguishable without relying on color.

●Links have a discernible name

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

●Touch targets have sufficient size and spacing.

●`[lang]` attributes have a valid value

●Heading elements appear in a sequentially-descending order

●Document has a main landmark.

●Deprecated ARIA roles were not used

●`<video>` elements contain a `<track>` element with `[kind="captions"]`

●Uses ARIA roles only on compatible elements

○`[accesskey]` values are unique

○ARIA input fields have accessible names

○ARIA `meter` elements have accessible names

○ARIA `progressbar` elements have accessible names

○Elements with the `role=text` attribute do not have focusable descendents.

○ARIA toggle fields have accessible names

○ARIA `tooltip` elements have accessible names

○ARIA `treeitem` elements have accessible names

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

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

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

○ARIA IDs are unique

○No form fields have multiple labels

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

○`<html>` element has an `[xml:lang]` attribute with the same base language as the `[lang]` attribute.

○Input buttons have discernible text.

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

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

○`<object>` elements have alternate text

○Select elements have associated label elements.

○Skip links are focusable.

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

○`<th>` elements and elements with `[role="columnheader"/"rowheader"]` have data cells they describe.

○Tables have different content in the summary attribute and `<caption>`.

○All heading elements contain content.

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

○Identical links have the same purpose.

○Tables use `<caption>` instead of cells with the `[colspan]` attribute to indicate a caption.

○`<td>` elements in a large `<table>` have one or more table headers.

Best Practices

General

Deprecated APIs will eventually be removed from the browser. Learn more about deprecated APIs.

Why this matters

Performance issues directly impact user engagement and conversion rates.

Deprecation / Warning	Source
SharedStorage	www.britishmuseum.org/cdn-cgi/challenge-platform/scripts/jsd/main.js
StorageType.persistent is deprecated. Please use standardized navigator.storage instead.	www.britishmuseum.org/cdn-cgi/challenge-platform/scripts/jsd/main.js
Fledge	www.britishmuseum.org/cdn-cgi/challenge-platform/scripts/jsd/main.js

●Uses HTTPS

●Avoids third-party cookies

●Allows users to paste into input fields

●Avoids requesting the geolocation permission on page load

●Avoids requesting the notification permission on page load

●Displays images with correct aspect ratio

●Serves images with appropriate resolution

●Page has the HTML doctype

●Properly defines charset

●No browser errors logged to the console

●No issues in the `Issues` panel in Chrome Devtools

●Ensure CSP is effective against XSS attacks

●Use a strong HSTS policy

●Ensure proper origin isolation with COOP

●Mitigate DOM-based XSS with Trusted Types

●Detected JavaScript libraries

●Page has valid source maps

○Redirects HTTP traffic to HTTPS

○Mitigate clickjacking with XFO or CSP

SEO

These checks ensure that your page is following basic search engine optimization advice. There are many additional factors Lighthouse does not score here that may affect your search ranking, including performance on Core Web Vitals. Learn more about Google Search Essentials.

Crawling and Indexing

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

Why this matters

Performance issues directly impact user engagement and conversion rates.

Uncrawlable Link
partners `div#ckb-content-consent > div.ckb-modal__text > p > a`
details section `div#ckb-content-consent > div.ckb-modal__text > p > a`

To appear in search results, crawlers need access to your app.

○Structured data is valid

●Page isn’t blocked from indexing

●Document has a `<title>` element

●Document has a meta description

●Page has successful HTTP status code

●Links have descriptive text

●robots.txt is valid

●Image elements have `[alt]` attributes

●Document has a valid `hreflang`

●Document has a valid `rel=canonical`