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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.

64

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.

Layout shifts occur when elements move absent any user interaction. Investigate the causes of layout shifts, such as elements being added, removed, or their fonts changing as the page loads.

Why this matters

Performance issues directly impact user engagement and conversion rates.

headings: [map[key:node label:Element subItemsHeading:map[key:extra] valueType:node] map[granularity:0.001 key:score label:Layout shift score subItemsHeading:map[key:cause valueType:text] valueType:numeric]]
items: [map[node:map[type:text value:Total] score:0.16381800000000002] map[node:map[boundingRect:map[bottom:1086 height:768 left:0 right:1350 top:318 width:1350] lhId:page-18-DIV nodeLabel:資料を検索 ピックアップ 「国立国会図書館ビジョン2026-2030―共につくる知の循環―」を公表しました 新規資料約60点を加えてリニューアル公開　電子… path:1,HTML,1,BODY,0,DIV,0,DIV,6,MAIN,3,DIV,2,DIV,0,DIV,2,DIV selector:div#main > div.base-layout-container > div.base-layout-container-inner > div.base-layout-full-width snippet:<div class="base-layout-full-width pages-hp-pickups" data-v-e83a083d="" data-v-1332f0f6=""> type:node] score:0.127974 subItems:map[items:[map[cause:Unsized image element extra:map[boundingRect:map[bottom:700 height:211 left:99 right:467 top:489 width:368] lhId:page-0-IMG nodeLabel:「国立国会図書館ビジョン2026-2030―共につくる知の循環―」のキービジュアル path:1,HTML,1,BODY,0,DIV,0,DIV,6,MAIN,3,DIV,2,DIV,0,DIV,2,DIV,1,DIV,0,DIV,3,DIV,2,UL,1,LI,0,A,1,IMG selector:ul.pages-hp-pickups-grid > li.pages-hp-pickup > a.lang-link > img snippet:<img class="" src="/file/part/top/pickups/main_jp.webp" alt="「国立国会図書館ビジョン2026-2030―共につくる知の循環―」のキービジュアル" data-v-e83a083d=""> type:node]]] type:subitems]] map[node:map[boundingRect:map[bottom:1553 height:467 left:99 right:1251 top:1086 width:1152] lhId:page-4-DIV nodeLabel:おしらせ RSS すべて プレスリリース ニュース イベント・展示会 刊行物 採用情報 サービス提供情報 2026年4月17日 ゴールデンウィークを含む期間… path:1,HTML,1,BODY,0,DIV,0,DIV,6,MAIN,3,DIV,2,DIV,0,DIV,3,DIV selector:div#main > div.base-layout-container > div.base-layout-container-inner > div.base-layout-column snippet:<div class="base-layout-column pages-hp-top-news" data-v-e4b04005="" data-v-651af461=""> type:node] score:0.027719 subItems:map[items:[map[cause:Unsized image element extra:map[boundingRect:map[bottom:696 height:207 left:491 right:859 top:489 width:368] lhId:page-19-IMG nodeLabel:電子展示会「あの人の直筆」トップページのイメージ画像 path:1,HTML,1,BODY,0,DIV,0,DIV,6,MAIN,3,DIV,2,DIV,0,DIV,2,DIV,1,DIV,0,DIV,3,DIV,2,UL,2,LI,0,A,1,IMG selector:ul.pages-hp-pickups-grid > li.pages-hp-pickup > a.lang-link > img snippet:<img class="" src="/file/part/top/pickups/jikihitsu_pickup.webp" alt="電子展示会「あの人の直筆」トップページのイメージ画像" data-v-e83a083d=""> type:node]] map[cause:Web font extra:map[type:url value:https://www.ndl.go.jp/assets/fonts/NotoSansJP-Regular.woff2]]] type:subitems]] map[node:map[boundingRect:map[bottom:1162 height:36 left:99 right:1251 top:1126 width:1152] lhId:page-8-H2 nodeLabel:おしらせ RSS path:1,HTML,1,BODY,0,DIV,0,DIV,6,MAIN,3,DIV,2,DIV,0,DIV,3,DIV,1,H2 selector:div.base-layout-container > div.base-layout-container-inner > div.base-layout-column > h2.base-heading snippet:<h2 class="base-heading is-h2" data-v-e4b04005="" data-v-6609c3c6=""> type:node] score:0.006235 subItems:map[items:[map[cause:Unsized image element extra:map[boundingRect:map[bottom:996 height:207 left:99 right:467 top:789 width:368] lhId:page-20-IMG nodeLabel:国立国会図書館インターネット資料収集保存事業（WARP）では、ウェブサイトを保存しています。 path:1,HTML,1,BODY,0,DIV,0,DIV,6,MAIN,3,DIV,2,DIV,0,DIV,2,DIV,1,DIV,0,DIV,3,DIV,2,UL,4,LI,0,A,1,IMG selector:ul.pages-hp-pickups-grid > li.pages-hp-pickup > a.lang-link > img snippet:<img class="" src="/file/part/top/pickups/warp_pickup.webp" alt="国立国会図書館インターネット資料収集保存事業（WARP）では、ウェブサイトを保存しています。" data-v-e83a083d=""> type:node]] map[cause:Web font extra:map[type:url value:https://www.ndl.go.jp/assets/fonts/NotoSansJP-Medium.woff2]]] type:subitems]] map[node:map[boundingRect:map[bottom:1553 height:467 left:99 right:1251 top:1086 width:1152] lhId:page-4-DIV nodeLabel:おしらせ RSS すべて プレスリリース ニュース イベント・展示会 刊行物 採用情報 サービス提供情報 2026年4月17日 ゴールデンウィークを含む期間… path:1,HTML,1,BODY,0,DIV,0,DIV,6,MAIN,3,DIV,2,DIV,0,DIV,3,DIV selector:div#main > div.base-layout-container > div.base-layout-container-inner > div.base-layout-column snippet:<div class="base-layout-column pages-hp-top-news" data-v-e4b04005="" data-v-651af461=""> type:node] score:0.001628 subItems:map[items:[map[cause:Unsized image element extra:map[boundingRect:map[bottom:700 height:211 left:99 right:467 top:489 width:368] lhId:page-0-IMG nodeLabel:「国立国会図書館ビジョン2026-2030―共につくる知の循環―」のキービジュアル path:1,HTML,1,BODY,0,DIV,0,DIV,6,MAIN,3,DIV,2,DIV,0,DIV,2,DIV,1,DIV,0,DIV,3,DIV,2,UL,1,LI,0,A,1,IMG selector:ul.pages-hp-pickups-grid > li.pages-hp-pickup > a.lang-link > img snippet:<img class="" src="/file/part/top/pickups/main_jp.webp" alt="「国立国会図書館ビジョン2026-2030―共につくる知の循環―」のキービジュアル" data-v-e83a083d=""> type:node]]] type:subitems]] map[node:map[boundingRect:map[bottom:1553 height:467 left:99 right:1251 top:1086 width:1152] lhId:page-4-DIV nodeLabel:おしらせ RSS すべて プレスリリース ニュース イベント・展示会 刊行物 採用情報 サービス提供情報 2026年4月17日 ゴールデンウィークを含む期間… path:1,HTML,1,BODY,0,DIV,0,DIV,6,MAIN,3,DIV,2,DIV,0,DIV,3,DIV selector:div#main > div.base-layout-container > div.base-layout-container-inner > div.base-layout-column snippet:<div class="base-layout-column pages-hp-top-news" data-v-e4b04005="" data-v-651af461=""> type:node] score:0.000173 subItems:map[items:[map[cause:Unsized image element extra:map[boundingRect:map[bottom:996 height:207 left:99 right:467 top:789 width:368] lhId:page-20-IMG nodeLabel:国立国会図書館インターネット資料収集保存事業（WARP）では、ウェブサイトを保存しています。 path:1,HTML,1,BODY,0,DIV,0,DIV,6,MAIN,3,DIV,2,DIV,0,DIV,2,DIV,1,DIV,0,DIV,3,DIV,2,UL,4,LI,0,A,1,IMG selector:ul.pages-hp-pickups-grid > li.pages-hp-pickup > a.lang-link > img snippet:<img class="" src="/file/part/top/pickups/warp_pickup.webp" alt="国立国会図書館インターネット資料収集保存事業（WARP）では、ウェブサイトを保存しています。" data-v-e83a083d=""> type:node]]] type:subitems]]]

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:23.349 source:map[column:132657 line:101 type:source-location url:https://www.ndl.go.jp/_nuxt/xQirD6gr.js urlProvider:network]] map[reflowTime:11.06 source:map[column:167844 line:101 type:source-location url:https://www.ndl.go.jp/_nuxt/xQirD6gr.js urlProvider:network]] map[reflowTime:1.94 source:map[column:135153 line:101 type:source-location url:https://www.ndl.go.jp/_nuxt/xQirD6gr.js urlProvider:network]] map[reflowTime:0.828 source:map[column:58377 line:108 type:source-location url:https://www.ndl.go.jp/_nuxt/xQirD6gr.js urlProvider:network]]]

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:1868.9130009765624 label:Time to first byte subpart:timeToFirstByte] map[duration:457.3159990234375 label:Resource load delay subpart:resourceLoadDelay] map[duration:1893.919 label:Resource load duration subpart:resourceLoadDuration] map[duration:62.66 label:Element render delay subpart:elementRenderDelay]]
lhId: page-0-IMG
nodeLabel: 「国立国会図書館ビジョン2026-2030―共につくる知の循環―」のキービジュアル
path: 1,HTML,1,BODY,0,DIV,0,DIV,6,MAIN,3,DIV,2,DIV,0,DIV,2,DIV,1,DIV,0,DIV,3,DIV,2,UL,1,LI,0,A,1,IMG
selector: ul.pages-hp-pickups-grid > li.pages-hp-pickup > a.lang-link > img
snippet: <img class="" src="/file/part/top/pickups/main_jp.webp" alt="「国立国会図書館ビジョン2026-2030―共につくる知の循環―」のキービジュアル" data-v-e83a083d="">

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-0-IMG
nodeLabel: 「国立国会図書館ビジョン2026-2030―共につくる知の循環―」のキービジュアル
path: 1,HTML,1,BODY,0,DIV,0,DIV,6,MAIN,3,DIV,2,DIV,0,DIV,2,DIV,1,DIV,0,DIV,3,DIV,2,UL,1,LI,0,A,1,IMG
selector: ul.pages-hp-pickups-grid > li.pages-hp-pickup > a.lang-link > img
snippet: <img class="" src="/file/part/top/pickups/main_jp.webp" alt="「国立国会図書館ビジョン2026-2030―共につくる知の循環―」のキービジュアル" data-v-e83a083d="">

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

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
「科学技術に関する調査プロジェクト」の報告書を刊行 ul.pages-hp-pickups-grid > li.pages-hp-pickup > a.lang-link > img
www.ndl.go.jp/file/part/top/pickups/R7kagipro.webp549.5 KiB537.1 KiB
「全国書誌データ検索」の特徴について示した図です。「全国書誌データ検索」は、国立国会図書館が作成した豊富な書誌データを収録しており、便利な検索機能や書誌のダウ… ul.pages-hp-pickups-grid > li.pages-hp-pickup > a.lang-link > img
www.ndl.go.jp/file/part/top/pickups/bib_search.webp389.8 KiB377.4 KiB
YouTube li.base-layout-column > a.lang-link > div > img
www.ndl.go.jp/assets/images/brand/youtube.png41.5 KiB41.3 KiB
国会事故調 div.base-layout-container-inner > div.base-layout-row > a.lang-link > img.base-image
www.ndl.go.jp/assets/images/naiic.png12.4 KiB10.9 KiB

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 Size
www.ndl.go.jp/_nuxt/index.CVPa9HsH.css2.6 KiB
www.ndl.go.jp/_nuxt/entry.BvlraQy1.css37.4 KiB

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: 418 ms
URLTime Spent
ndl.go.jp/418 ms
www.ndl.go.jp/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: 1.1 s
URLTime Spent
www.ndl.go.jp/1.2 s

These are the largest layout shifts observed on the page. Each table item represents a single layout shift, and shows the element that shifted the most. Below each item are possible root causes that led to the layout shift. Some of these layout shifts may not be included in the CLS metric value due to windowing. Learn how to improve CLS

Why this matters

Performance issues directly impact user engagement and conversion rates.

ElementLayout shift score
資料を検索 ピックアップ 「国立国会図書館ビジョン2026-2030―共につくる知の循環―」を公表しました 新規資料約60点を加えてリニューアル公開　電子… div#main > div.base-layout-container > div.base-layout-container-inner > div.base-layout-full-width
0.128
おしらせ RSS すべて プレスリリース ニュース イベント・展示会 刊行物 採用情報 サービス提供情報 2026年4月17日 ゴールデンウィークを含む期間… div#main > div.base-layout-container > div.base-layout-container-inner > div.base-layout-column
0.028
おしらせ RSS div.base-layout-container > div.base-layout-container-inner > div.base-layout-column > h2.base-heading
0.006
おしらせ RSS すべて プレスリリース ニュース イベント・展示会 刊行物 採用情報 サービス提供情報 2026年4月17日 ゴールデンウィークを含む期間… div#main > div.base-layout-container > div.base-layout-container-inner > div.base-layout-column
0.002
おしらせ RSS すべて プレスリリース ニュース イベント・展示会 刊行物 採用情報 サービス提供情報 2026年4月17日 ゴールデンウィークを含む期間… div#main > div.base-layout-container > div.base-layout-container-inner > div.base-layout-column
0.000
令和7年度「科学技術に関する調査プロジェクト」の報告書3点を刊行 ul.pages-hp-pickups-grid > li.pages-hp-pickup > a.lang-link > p
0.000
より見やすく、使いやすくなったひなぎくをぜひご覧ください ul.pages-hp-pickups-grid > li.pages-hp-pickup > a.lang-link > p
0.000
国立国会図書館でのクッキーの使用 div.layouts-global > div#layer-notification > div.base-panel > h3.base-heading
0.000

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: 0.0 ms 32.8 KiB
URLTransfer SizeEst Savings
www.ndl.go.jp/_nuxt/entry.BvlraQy1.css36.3 KiB32.8 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: 360 ms 464.9 KiB
URLTransfer SizeEst Savings
www.ndl.go.jp/_nuxt/xQirD6gr.js1.0 MiB464.9 KiB

Many navigations are performed by going back to a previous page, or forwards again. The back/forward cache (bfcache) can speed up these return navigations. Learn more about the bfcache

Why this matters

Performance issues directly impact user engagement and conversion rates.

Failure reasonFailure type
Pages whose main resource has cache-control:no-store cannot enter back/forward cache.Not actionable
Back/forward cache is disabled because some JavaScript network request received resource with Cache-Control: no-store header.Not actionable

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.ndl.go.jp/_nuxt/xQirD6gr.js1.1 MiB
www.ndl.go.jp/file/part/top/pickups/R7kagipro.webp550.6 KiB
www.ndl.go.jp/file/part/top/pickups/bib_search.webp390.8 KiB
www.ndl.go.jp/assets/fonts/NotoSansJP-Bold.woff2302.1 KiB
www.ndl.go.jp/assets/fonts/NotoSansJP-Medium.woff2299.6 KiB
www.ndl.go.jp/assets/fonts/NotoSansJP-Regular.woff2296.2 KiB
www.ndl.go.jp/file/part/top/pickups/main_jp.webp172.5 KiB
www.ndl.go.jp/file/part/top/pickups/warp_pickup.webp127.4 KiB
www.ndl.go.jp/file/part/top/pickups/jikihitsu_pickup.webp62.7 KiB
www.ndl.go.jp/file/part/top/pickups/hinagiku_renewal_jp.webp56.9 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
「国立国会図書館ビジョン2026-2030―共につくる知の循環―」のキービジュアル ul.pages-hp-pickups-grid > li.pages-hp-pickup > a.lang-link > img
www.ndl.go.jp/file/part/top/pickups/main_jp.webp
「震災に関するあらゆる記録・教訓を、次の世代へ」。国立国会図書館東日本大震災アーカイブ（ひなぎく）は2026年3月にリニューアルしました。 ul.pages-hp-pickups-grid > li.pages-hp-pickup > a.lang-link > img
www.ndl.go.jp/file/part/top/pickups/hinagiku_renewal_jp.webp
「科学技術に関する調査プロジェクト」の報告書を刊行 ul.pages-hp-pickups-grid > li.pages-hp-pickup > a.lang-link > img
www.ndl.go.jp/file/part/top/pickups/R7kagipro.webp
「全国書誌データ検索」の特徴について示した図です。「全国書誌データ検索」は、国立国会図書館が作成した豊富な書誌データを収録しており、便利な検索機能や書誌のダウ… ul.pages-hp-pickups-grid > li.pages-hp-pickup > a.lang-link > img
www.ndl.go.jp/file/part/top/pickups/bib_search.webp
電子展示会「あの人の直筆」トップページのイメージ画像 ul.pages-hp-pickups-grid > li.pages-hp-pickup > a.lang-link > img
www.ndl.go.jp/file/part/top/pickups/jikihitsu_pickup.webp
国立国会図書館インターネット資料収集保存事業（WARP）では、ウェブサイトを保存しています。 ul.pages-hp-pickups-grid > li.pages-hp-pickup > a.lang-link > img
www.ndl.go.jp/file/part/top/pickups/warp_pickup.webp
国会事故調 div.base-layout-container-inner > div.base-layout-row > a.lang-link > img.base-image
www.ndl.go.jp/assets/images/naiic.png
X li.base-layout-column > a.lang-link > div > img
www.ndl.go.jp/assets/images/brand/x.png
YouTube li.base-layout-column > a.lang-link > div > img
www.ndl.go.jp/assets/images/brand/youtube.png

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

●Max Potential First Input Delay 110 ms
●Use efficient cache lifetimes
●Optimize DOM size
●Font display
●Modern HTTP
●Optimize viewport for mobile
●Minify CSS
●Minify JavaScript
●JavaScript execution time 0.3 s
●Minimizes main-thread work 0.8 s
●Avoid long main-thread tasks 2 long tasks found
●Network Requests
●Network Round Trip Times 0 ms
●Server Backend Latencies 590 ms
●Tasks
●Diagnostics
●Metrics
●Screenshot Thumbnails
●Final Screenshot
●Script Treemap Data
●Resources Summary
○INP breakdown
○User Timing marks and measures
○Avoid non-composited animations
89

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.

Names and labels

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 how to make buttons more accessible.

Why this matters

Performance issues directly impact user engagement and conversion rates.

Failing Elements
div.base-layout-column > div.base-layout-column > a > button.base-button div.base-layout-column > div.base-layout-column > a > button.base-button
div.base-layout-column > div.base-layout-column > a > button.base-button div.base-layout-column > div.base-layout-column > a > button.base-button
div.base-layout-column > div.base-layout-column > a > button.base-button div.base-layout-column > div.base-layout-column > a > button.base-button

These are opportunities to improve the semantics of the controls in your application. This 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
X div.base-layout-column > ul.base-layout-row > li.base-layout-column > ul.base-layout-column

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
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YouTube li.base-layout-column > ul.base-layout-column > div.base-layout-row > li.base-layout-column

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

○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
●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
●`[aria-*]` attributes have valid values
●`[aria-*]` attributes are valid and not misspelled
●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.
●Select elements have associated label elements.
●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 have a discernible name
●No element has a `[tabindex]` value greater than 0
●Touch targets have sufficient size and spacing.
●Heading elements appear in a sequentially-descending order
●Document has a main landmark.
●Deprecated ARIA roles were not used
●Elements with visible text labels have matching accessible names.
○`[accesskey]` values are unique
○`button`, `link`, and `menuitem` elements have accessible names
○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
○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
○Links are distinguishable without relying on color.
○The document does not use `<meta http-equiv="refresh">`
○`<object>` elements have alternate text
○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.
○`[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.
○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.
100

Best Practices

General

Source maps translate minified code to the original source code. This helps developers debug in production. In addition, Lighthouse is able to provide further insights. Consider deploying source maps to take advantage of these benefits. Learn more about source maps.

Why this matters

Performance issues directly impact user engagement and conversion rates.

URL
www.ndl.go.jp/_nuxt/xQirD6gr.js
●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 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
○Redirects HTTP traffic to HTTPS
○Mitigate clickjacking with XFO or CSP
○Detected JavaScript libraries
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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.

○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
●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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