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

Audit breakdown by category with detailed findings.

60

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.

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.

RequestCache TTLTransfer Size
www.cwi.nl/images/58806/La_gata_perduda_verbeterd.2e16d0ba.fill-1920x866.png0.0 ms1.8 MiB
www.cwi.nl/images/58186/Algemeen_CWI_2025_06_04-017.2e16d0ba.fill-1920x866.jpg0.0 ms246.4 KiB
/images/59161/CWI_SEN_Symposium_2025_aangepast.e4af3d34.f...0.0 ms240.0 KiB
www.cwi.nl/static/main-c4db4aa6310f0cf78ada.css0.0 ms238.5 KiB
www.cwi.nl/images/59065/lynda_hardman_award.2e16d0ba.fill-427x427.png0.0 ms238.2 KiB
www.cwi.nl/images/58189/DIS-groep_CWI_2025_06_04-014.2e16d0ba.fill-1920x866.jpg0.0 ms219.9 KiB
www.cwi.nl/images/58188/Algemeen_CWI_2025_06_04-008.2e16d0ba.fill-1920x866.jpg0.0 ms207.5 KiB
www.cwi.nl/images/34465/221208-headerbeeld-07.2e16d0ba.fill-1920x866.jpg0.0 ms196.8 KiB
www.cwi.nl/static/ea44293bc5ac1d356409.png0.0 ms167.2 KiB
www.cwi.nl/static/main-c4db4aa6310f0cf78ada.js0.0 ms137.7 KiB
www.cwi.nl/images/59036/CWI_Algemeen_20_10_04-097.0038b6f3.fill-427x427.jpg0.0 ms52.7 KiB
www.cwi.nl/static/2f02effe392a63dc07a5.woff20.0 ms34.3 KiB
/images/58992/Laura-Hollink__Beta_2026_Harold-va.de4a18fb...0.0 ms30.5 KiB
www.cwi.nl/static/images/nwo-logo.svg0.0 ms24.4 KiB
stats.cwi.nl/piwik.js0.0 ms20.6 KiB
www.cwi.nl/static/images/logos/cwi-logo-english-white.svg0.0 ms17.9 KiB
www.cwi.nl/documents/200032/80_YearLogo_Teal_Text_alleen_voor_website.svg0.0 ms7.7 KiB
www.cwi.nl/jsi18n/0.0 ms3.4 KiB
www.cwi.nl/static/images/triangle.svg0.0 ms630 B

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.

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.

URLResource SizeEst Savings
Featured In Barcelona, 200 residents co-created an award-winning opera, as par… main#content > div.homepage-slider > div.swiper-wrapper > div.swiper-slide
www.cwi.nl/images/58806/La_gata_perduda_verbeterd.2e16d0ba.fill-1920x866.png1.8 MiB1.6 MiB
Chair of SEN symposium announcing award div.block_wrapper > div.news-list__grid > a.news-list__item > img.news-list__item-image
/images/59161/CWI_SEN_Symposium_2025_aangepast.e4af3d34.f...239.5 KiB209.8 KiB
Lynda Hardman poses with her award together with another award winner. div.block_wrapper > div.news-list__grid > a.news-list__item > img.news-list__item-image
www.cwi.nl/images/59065/lynda_hardman_award.2e16d0ba.fill-427x427.png237.7 KiB208.0 KiB
div.block_wrapper > div.news-list__grid > a.news-list__item > img.news-list__item-image div.block_wrapper > div.news-list__grid > a.news-list__item > img.news-list__item-image
www.cwi.nl/images/59036/CWI_Algemeen_20_10_04-097.0038b6f3.fill-427x427.jpg52.3 KiB22.7 KiB

Each subpart has specific improvement strategies. Ideally, most of the LCP time should be spent on loading the resources, not within delays.

Why this matters

Performance issues directly impact user engagement and conversion rates.

headings: [map[key:label label:Subpart valueType:text] map[key:duration label:Duration valueType:ms]]
items: [map[duration:2183.666 label:Time to first byte subpart:timeToFirstByte] map[duration:654.234 label:Resource load delay subpart:resourceLoadDelay] map[duration:488.081 label:Resource load duration subpart:resourceLoadDuration] map[duration:216.631 label:Element render delay subpart:elementRenderDelay]]
lhId: page-4-DIV
nodeLabel: Featured In Barcelona, 200 residents co-created an award-winning opera, as par…
path: 1,HTML,1,BODY,4,MAIN,1,DIV,0,DIV,1,DIV
selector: main#content > div.homepage-slider > div.swiper-wrapper > div.swiper-slide
snippet: <div class="swiper-slide homepage-slider__image swiper-slide-visible swiper-slide-acti…" style="background-image: url(&quot;/images/58806/La_gata_perduda_verbeterd.2e16d0ba.fi…&quot;);" data-swiper-slide-index="0">

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-4-DIV
nodeLabel: Featured In Barcelona, 200 residents co-created an award-winning opera, as par…
path: 1,HTML,1,BODY,4,MAIN,1,DIV,0,DIV,1,DIV
selector: main#content > div.homepage-slider > div.swiper-wrapper > div.swiper-slide
snippet: <div class="swiper-slide homepage-slider__image swiper-slide-visible swiper-slide-acti…" style="background-image: url(&quot;/images/58806/La_gata_perduda_verbeterd.2e16d0ba.fi…&quot;);" data-swiper-slide-index="0">

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
value: no origins were preconnected
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.

URLTransfer SizeDuration
www.cwi.nl/static/main-c4db4aa6310f0cf78ada.css238.5 KiB244 ms

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: 1.4 s
URLTime Spent
cwi.nl/635 ms
www.cwi.nl/784 ms
www.cwi.nl/en/0.0 ms

Keep the server response time for the main document short because all other requests depend on it. Learn more about the Time to First Byte metric.

Why this matters

Performance issues directly impact user engagement and conversion rates.

Estimated savings: 802 ms
URLTime Spent
www.cwi.nl/en/902 ms

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: 180 ms 215.4 KiB
URLTransfer SizeEst Savings
www.cwi.nl/static/main-c4db4aa6310f0cf78ada.css238.0 KiB215.4 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: 180 ms 112.1 KiB
URLTransfer SizeEst Savings
www.cwi.nl/static/main-c4db4aa6310f0cf78ada.js137.3 KiB77.3 KiB
cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.9/config/TeX-MML-AM_CHTML.js?V=2.7.964.9 KiB34.8 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.

URLTransfer Size
www.cwi.nl/images/58806/La_gata_perduda_verbeterd.2e16d0ba.fill-1920x866.png1.8 MiB
www.cwi.nl/images/58186/Algemeen_CWI_2025_06_04-017.2e16d0ba.fill-1920x866.jpg246.4 KiB
/images/59161/CWI_SEN_Symposium_2025_aangepast.e4af3d34.f...240.0 KiB
www.cwi.nl/static/main-c4db4aa6310f0cf78ada.css238.5 KiB
www.cwi.nl/images/59065/lynda_hardman_award.2e16d0ba.fill-427x427.png238.2 KiB
www.cwi.nl/images/58189/DIS-groep_CWI_2025_06_04-014.2e16d0ba.fill-1920x866.jpg219.9 KiB
www.cwi.nl/images/58188/Algemeen_CWI_2025_06_04-008.2e16d0ba.fill-1920x866.jpg207.5 KiB
www.cwi.nl/images/34465/221208-headerbeeld-07.2e16d0ba.fill-1920x866.jpg196.8 KiB
www.cwi.nl/static/ea44293bc5ac1d356409.png167.2 KiB
www.cwi.nl/static/main-c4db4aa6310f0cf78ada.js137.7 KiB

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

Why this matters

Performance issues directly impact user engagement and conversion rates.

URL
Chair of SEN symposium announcing award div.block_wrapper > div.news-list__grid > a.news-list__item > img.news-list__item-image
/images/59161/CWI_SEN_Symposium_2025_aangepast.e4af3d34.f...
Lynda Hardman poses with her award together with another award winner. div.block_wrapper > div.news-list__grid > a.news-list__item > img.news-list__item-image
www.cwi.nl/images/59065/lynda_hardman_award.2e16d0ba.fill-427x427.png
div.block_wrapper > div.news-list__grid > a.news-list__item > img.news-list__item-image div.block_wrapper > div.news-list__grid > a.news-list__item > img.news-list__item-image
www.cwi.nl/images/59036/CWI_Algemeen_20_10_04-097.0038b6f3.fill-427x427.jpg
Laura Hollink div.block_wrapper > div.news-list__grid > a.news-list__item > img.news-list__item-image
/images/58992/Laura-Hollink__Beta_2026_Harold-va.de4a18fb...
CWI logo body > div.pre-footer > div.pre-footer__content > img.pre-footer__logo
www.cwi.nl/static/images/logos/cwi-logo-english-white.svg
NWO logo div.footer__column > div.footer__nwo-wrapper > a > img
www.cwi.nl/static/images/nwo-logo.svg

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
●Forced reflow
●Modern HTTP
●Optimize viewport for mobile
●Max Potential First Input Delay 20 ms
●Minify CSS
●Minify JavaScript
●JavaScript execution time 0.1 s
●Minimizes main-thread work 0.4 s
●Page didn't prevent back/forward cache restoration
●Network Requests
●Network Round Trip Times 150 ms
●Server Backend Latencies 150 ms
●Tasks
●Diagnostics
●Metrics
●Screenshot Thumbnails
●Final Screenshot
●Script Treemap Data
●Resources Summary
●Avoid large layout shifts 2 layout shifts found
○INP breakdown
○User Timing marks and measures
○Avoid long main-thread tasks
○Avoid non-composited animations
91

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.

Contrast

Low-contrast text is difficult or impossible for many users to read. Learn how to provide sufficient color contrast.

Why this matters

Performance issues directly impact user engagement and conversion rates.

Failing Elements
Research nav.header__primary-nav > ul.header__primary-nav-links > li.header__primary-nav-item > button.header__primary-nav-link
Education nav.header__primary-nav > ul.header__primary-nav-links > li.header__primary-nav-item > button.header__primary-nav-link
Results nav.header__primary-nav > ul.header__primary-nav-links > li.header__primary-nav-item > button.header__primary-nav-link
News nav.header__primary-nav > ul.header__primary-nav-links > li.header__primary-nav-item > button.header__primary-nav-link
Events nav.header__primary-nav > ul.header__primary-nav-links > li.header__primary-nav-item > button.header__primary-nav-link
Collaboration nav.header__primary-nav > ul.header__primary-nav-links > li.header__primary-nav-item > button.header__primary-nav-link
Work@CWI nav.header__primary-nav > ul.header__primary-nav-links > li.header__primary-nav-item > button.header__primary-nav-link
About nav.header__primary-nav > ul.header__primary-nav-links > li.header__primary-nav-item > button.header__primary-nav-link

These are opportunities to improve the legibility of your content.

Best practices

Touch targets with sufficient size and spacing help users who may have difficulty targeting small controls to activate the targets. Learn more about touch targets.

Why this matters

Performance issues directly impact user engagement and conversion rates.

Failing Elements
+31 20 592 9333 div > ul.footer__contact > li.footer__contact-item > a.footer__contact-link
info@cwi.nl div > ul.footer__contact > li.footer__contact-item > a.footer__contact-link

These items highlight common accessibility best practices.

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
Research nav.header__primary-nav > ul.header__primary-nav-links > li.header__primary-nav-item > button.header__primary-nav-link
Education nav.header__primary-nav > ul.header__primary-nav-links > li.header__primary-nav-item > button.header__primary-nav-link
Results nav.header__primary-nav > ul.header__primary-nav-links > li.header__primary-nav-item > button.header__primary-nav-link
News nav.header__primary-nav > ul.header__primary-nav-links > li.header__primary-nav-item > button.header__primary-nav-link
Events nav.header__primary-nav > ul.header__primary-nav-links > li.header__primary-nav-item > button.header__primary-nav-link
Collaboration nav.header__primary-nav > ul.header__primary-nav-links > li.header__primary-nav-item > button.header__primary-nav-link
Work@CWI nav.header__primary-nav > ul.header__primary-nav-links > li.header__primary-nav-item > button.header__primary-nav-link
About nav.header__primary-nav > ul.header__primary-nav-links > li.header__primary-nav-item > button.header__primary-nav-link
○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>`
●`[aria-*]` attributes have valid values
●`[aria-*]` attributes are valid and not misspelled
●Buttons have an accessible name
●Image elements have `[alt]` attributes
●`[user-scalable="no"]` is not used in the `<meta name="viewport">` element and the `[maximum-scale]` attribute is not less than 5.
●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
●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
●Lists contain only `<li>` elements and script supporting elements (`<script>` and `<template>`).
●List items (`<li>`) are contained within `<ul>`, `<ol>` or `<menu>` parent elements
●Heading elements appear in a sequentially-descending order
●Skip links are focusable.
●Document has a main landmark.
●Identical links have the same purpose.
○`[accesskey]` values are unique
○`button`, `link`, and `menuitem` elements have accessible names
○Deprecated ARIA roles were not used
○Elements with `role="dialog"` or `role="alertdialog"` have accessible names.
○ARIA input fields have accessible names
○ARIA `meter` elements have accessible names
○ARIA `progressbar` elements have accessible names
○`[role]`s have all required `[aria-*]` attributes
○Elements with an ARIA `[role]` that require children to contain a specific `[role]` have all required children.
○`[role]`s are contained by their required parent element
○`[role]` values are valid
○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
○Form elements have associated labels
○The document does not use `<meta http-equiv="refresh">`
○`<object>` elements have alternate text
○Select elements have associated label elements.
○No element has a `[tabindex]` value greater than 0
○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.
○`[lang]` attributes have a valid value
○`<video>` elements contain a `<track>` element with `[kind="captions"]`
○Tables have different content in the summary attribute and `<caption>`.
○All heading elements contain content.
○Uses ARIA roles only on compatible elements
○Image elements do not have `[alt]` attributes that are redundant text.
○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.
96

Best Practices

General

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

Why this matters

Performance issues directly impact user engagement and conversion rates.

SourceDescription
www.cwi.nl/static/main-c4db4aa6310f0cf78ada.js line 1, col 139846
TypeError: Cannot read properties of null (reading 'addEventListener') at https://www.cwi.nl/static/main-c4db4aa6310f0cf78ada.js:2:139847 at https://www.cwi.nl/static/main-c4db4aa6310f0cf78ada.js:2:139900 at https://www.cwi.nl/static/main-c4db4aa6310f0cf78ada.js:2:140531 at https://www.cwi.nl/static/main-c4db4aa6310f0cf78ada.js:2:140535
●Uses HTTPS
●Avoids deprecated APIs
●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 issues in the `Issues` panel in Chrome Devtools
●Ensure CSP is effective against XSS attacks
●Use a strong HSTS policy
●Mitigate DOM-based XSS with Trusted Types
●Page has valid source maps
○Redirects HTTP traffic to HTTPS
○Ensure proper origin isolation with COOP
○Mitigate clickjacking with XFO or CSP
○Detected JavaScript libraries
83

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.

Content Best Practices

Meta descriptions may be included in search results to concisely summarize page content. Learn more about the meta description.

Why this matters

Performance issues directly impact user engagement and conversion rates.

Descriptive link text helps search engines understand your content. Learn how to make links more accessible.

Why this matters

Performance issues directly impact user engagement and conversion rates.

Link destinationLink Text
www.cwi.nl/en/stories/cwi-works-closely-with-universities/Read More
www.cwi.nl/en/stories/eu-funded-research-that-makes-a-difference/Read More
www.cwi.nl/en/research/innovation-research-focus-areas/Read More
www.cwi.nl/en/events/research-semester-programmes/Read More
www.cwi.nl/en/research/Read More
www.cwi.nl/en/stories/cwi-works-closely-with-universities/Read More
www.cwi.nl/en/stories/eu-funded-research-that-makes-a-difference/Read More
www.cwi.nl/en/about/Read More

Format your HTML in a way that enables crawlers to better understand your app’s content.

○Structured data is valid
●Page isn’t blocked from indexing
●Document has a `<title>` element
●Page has successful HTTP status code
●Links are crawlable
●robots.txt is valid
●Image elements have `[alt]` attributes
●Document has a valid `hreflang`
○Document has a valid `rel=canonical`

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