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https://bnf.fr

Performance

· 15 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
76
GRADE
C
FIX
4
REVIEW
4
PASS
5
INFO
2

Performance-focused optimization plan with CWV assessment, top offenders, and time estimates

Mobile Desktop
59
Performance Overall performance score (0–100) based on Core Web Vitals and other metrics. 90+ is good.
98
Accessibility Measures how accessible the page is for users with disabilities. Checks color contrast, ARIA labels, and semantic HTML.
100
Best Practices Checks for modern web development best practices including HTTPS, no console errors, and secure JavaScript.
100
SEO Measures basic SEO optimizations: meta tags, crawlability, link text, and mobile friendliness.

First Contentful Paint First Contentful Paint — how long until the browser renders the first piece of content. Under 1.8s is good.

3.90 s

Largest Contentful Paint Largest Contentful Paint — how long until the largest visible element loads. Under 2.5s is good.

4.38 s

Total Blocking Time Total Blocking Time — total time the main thread was blocked, preventing user input. Under 200ms is good.

11 ms

Cumulative Layout Shift Cumulative Layout Shift — measures visual stability. How much the page layout shifts during loading. Under 0.1 is good.

0.008

Speed Index Speed Index — how quickly content is visually displayed during load. Under 3.4s is good.

4.74 s

Time to Interactive Time to Interactive — how long until the page is fully interactive and responds to user input. Under 3.8s is good.

4.43 s

Page Load Progression

779 ms
1.6 s
2.3 s
3.1 s
3.9 s
4.7 s
5.5 s
6.2 s
Checks
15
5 PASS 4 REVIEW 4 FIX
D
Third-Party Impact
Action
100% third-party, 0 ms blocking
FIX
100% third-party, 0 ms blocking
Warning::
Third-party code accounts for 100% of page weight (2.0 MiB of 2.0 MiB)
Info::
Third-party blocking time is low (0 ms)
100%
First-party Third-party
D
JS Bundles
Action
9 scripts, 239 KB unused
FIX
9 scripts, 239 KB unused
Warning::
https://www.bnf.fr/sites/default/files/js/js_ogHJM...: 192 KB unused (80%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.bnf.fr/sites/default/files/js/js_ogHJM...: unminified — 36 KB could be saved
Warning::
https://cdn.tarteaucitron.io/tarteaucitron.service...: 27 KB unused (75%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://static.addtoany.com/menu/modules/core.ydpp...: 21 KB unused (82%)
Consider code splitting or tree shaking to reduce unused code.
Info::
Total unused JavaScript: 239 KB
239 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://www.bnf.fr/sites/default/files/js/js_ogHJM-y5BPuXvT1_XF46lI_uNY5jd0mbO_CLaUb3JOs.js241 KB192 KB (80%)✗3rd
https://cdn.tarteaucitron.io/tarteaucitron.services.min.js?v=1.32.036 KB27 KB (75%)✓3rd
https://static.addtoany.com/menu/modules/core.ydpp7jcu.js26 KB21 KB (82%)✓3rd
https://tag.aticdn.net/18798/smarttag.js26 KB—✓3rd
https://cdntag.tarteaucitron.io/load.js?domain=bnf.fr/fr&uuid=91ba7c974c752a888f0a2765181efcbea3a33ef922 KB—✓3rd
https://www.bnf.fr/sites/default/files/js/js_HCUq-SQK4ouQGcgWI_9vvAZpIAbwprXmQrtwZH11Z4w.js43 KB—✓3rd
https://static.addtoany.com/menu/page.js2 KB—✓3rd
blob:https://www.bnf.fr/9a724024-7cfb-460d-97a8-e871e4f064020 KB—✓3rd
https://cdn.tarteaucitron.io/lang/tarteaucitron.fr.min.js?v=1.32.02 KB—✓3rd

Consider code splitting or tree shaking to reduce unused code.

Why this matters

This bundle has high unused code — code-split or tree-shake to ship only what executes.

Source: web.dev / Lighthouse coverage

Consider code splitting or tree shaking to reduce unused code.

Why this matters

This bundle has high unused code — code-split or tree-shake to ship only what executes.

Source: web.dev / Lighthouse coverage

Consider code splitting or tree shaking to reduce unused code.

Why this matters

This bundle has high unused code — code-split or tree-shake to ship only what executes.

Source: web.dev / Lighthouse coverage

D
Page Weight Inventory
Action
74 resources · 2.0 MB · 239 KB savings available
FIX
74 resources · 2.0 MB · 239 KB savings available
Warning::
Page weight 1.0 MB over 1MB target
Got: 2.0 MB Expected: ≤ 1 MB
Info::
~239 KB of savings available
Warning::
73 third-party resources (100% of weight)
Info::
3 resources over 200KB
74 resources · 2.0 MiB · 73 third-party 1.0 MiB over 1MB target
Image 69% · 1.4 MiB
JavaScript 19% · 398.5 KiB
Font 5% · 109.9 KiB
CSS 5% · 103.1 KiB
Document 1% · 25.2 KiB
Other 0% · 86 B

~239.4 KiB of savings available

Remove unused JavaScript: 239.4 KiB
F
HTTP Caching
Action
No cache headers
FIX
No cache headers
Warning::
No Cache-Control header found
Browsers will use heuristic caching, which can be unpredictable. Set explicit cache headers.

No Cache-Control header

Adding a Cache-Control header can significantly improve repeat-visit performance.

C
Page Weight Budget
Action
2.0 MB transferred, 74 requests
REVIEW
2.0 MB transferred, 74 requests
Info::
Page weighs 3.9 MB (2.0 MB transferred)
Warning::
Images are 1.4 MB — compress or use modern formats
Convert images to WebP/AVIF and resize to display dimensions to reduce transfer size.
Got: 1.4 MB
Info::
74 HTTP requests
Info::
Estimated 0.42 g CO2 per page load
2.0 MB / 2.4 MB budget
2.0 MB transferred
74 requests
0.42 g CO2 per page load
Images 1.4 MiB 69%
JavaScript 398.5 KiB 19%
Fonts 109.9 KiB 5%
CSS 103.1 KiB 5%
HTML 24.5 KiB 1%
Other 983 B 0%
Other 86 B 0%
Other 0 B 0%
0 2.4 MB 4.9 MB
Approaching limit

Convert images to WebP/AVIF and resize to display dimensions to reduce transfer size.

Why this matters

Image bandwidth is high — modern formats (WebP/AVIF) and resizing typically cut it 50%+.

Source: web.dev

C
Image Optimization
Action
43 images, 0 KB saveable
REVIEW
43 images, 0 KB saveable
Warning::
https://www.bnf.fr/sites/default/files/styles/carr... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.bnf.fr/sites/default/files/svg/picto_m... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.bnf.fr/sites/default/files/svg/picto_m... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.bnf.fr/sites/default/files/svg/picto_i... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.bnf.fr/sites/default/files/styles/focu... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.bnf.fr/sites/default/files/svg/picto_h... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.bnf.fr/sites/default/files/svg/picto_a... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.bnf.fr/sites/default/files/styles/focu... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.bnf.fr/sites/default/files/svg/picto_c... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.bnf.fr/sites/default/files/inline-imag... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.bnf.fr/sites/default/files/2019-10/Pic... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.bnf.fr/sites/default/files/styles/focu... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.bnf.fr/sites/default/files/styles/carr... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.bnf.fr/sites/default/files/styles/carr... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.bnf.fr/sites/default/files/inline-imag... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.bnf.fr/sites/default/files/2019-04/Def... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
43 images 1.4 MB
0 oversized -0 KB
41 legacy format
16 missing dimensions CLS risk

Set explicit width and height to prevent CLS.

Why this matters

Image without explicit width/height — browser can't reserve space; CLS jumps when image loads.

Source: web.dev / Core Web Vitals

Set explicit width and height to prevent CLS.

Why this matters

Image without explicit width/height — browser can't reserve space; CLS jumps when image loads.

Source: web.dev / Core Web Vitals

Set explicit width and height to prevent CLS.

Why this matters

Image without explicit width/height — browser can't reserve space; CLS jumps when image loads.

Source: web.dev / Core Web Vitals

Set explicit width and height to prevent CLS.

Why this matters

Image without explicit width/height — browser can't reserve space; CLS jumps when image loads.

Source: web.dev / Core Web Vitals

Set explicit width and height to prevent CLS.

Why this matters

Image without explicit width/height — browser can't reserve space; CLS jumps when image loads.

Source: web.dev / Core Web Vitals

Set explicit width and height to prevent CLS.

Why this matters

Image without explicit width/height — browser can't reserve space; CLS jumps when image loads.

Source: web.dev / Core Web Vitals

Set explicit width and height to prevent CLS.

Why this matters

Image without explicit width/height — browser can't reserve space; CLS jumps when image loads.

Source: web.dev / Core Web Vitals

Set explicit width and height to prevent CLS.

Why this matters

Image without explicit width/height — browser can't reserve space; CLS jumps when image loads.

Source: web.dev / Core Web Vitals

Set explicit width and height to prevent CLS.

Why this matters

Image without explicit width/height — browser can't reserve space; CLS jumps when image loads.

Source: web.dev / Core Web Vitals

Set explicit width and height to prevent CLS.

Why this matters

Image without explicit width/height — browser can't reserve space; CLS jumps when image loads.

Source: web.dev / Core Web Vitals

Set explicit width and height to prevent CLS.

Why this matters

Image without explicit width/height — browser can't reserve space; CLS jumps when image loads.

Source: web.dev / Core Web Vitals

Set explicit width and height to prevent CLS.

Why this matters

Image without explicit width/height — browser can't reserve space; CLS jumps when image loads.

Source: web.dev / Core Web Vitals

Set explicit width and height to prevent CLS.

Why this matters

Image without explicit width/height — browser can't reserve space; CLS jumps when image loads.

Source: web.dev / Core Web Vitals

Set explicit width and height to prevent CLS.

Why this matters

Image without explicit width/height — browser can't reserve space; CLS jumps when image loads.

Source: web.dev / Core Web Vitals

Set explicit width and height to prevent CLS.

Why this matters

Image without explicit width/height — browser can't reserve space; CLS jumps when image loads.

Source: web.dev / Core Web Vitals

Set explicit width and height to prevent CLS.

Why this matters

Image without explicit width/height — browser can't reserve space; CLS jumps when image loads.

Source: web.dev / Core Web Vitals

B
JS Execution Cost
747ms total JS execution
REVIEW
747ms total JS execution
Warning::
https://www.bnf.fr/fr: 373ms CPU time
Info::
https://www.bnf.fr/sites/default/files/js/js_ogHJM...: 147ms CPU time
Info::
Unattributable: 144ms CPU time
Info::
https://www.bnf.fr/sites/default/files/js/js_HCUq-...: 82ms CPU time
Warning::
Third-party scripts: 747ms (100% of total)

Main Thread Breakdown

Other 41% Script Evaluation 24% Style & Layout 17% Script Parsing & Compilation 6% Parse HTML & CSS 6% Rendering 5%
ScriptTotalScriptingParse/CompileParty
https://www.bnf.fr/fr373ms19ms1ms3rd
https://www.bnf.fr/sites/default/files/js/js_ogHJM-y5BPuXvT1_XF46lI_uNY5jd0mbO_CLaUb3JOs.js147ms93ms33ms3rd
Unattributable144ms4ms0ms3rd
https://www.bnf.fr/sites/default/files/js/js_HCUq-SQK4ouQGcgWI_9vvAZpIAbwprXmQrtwZH11Z4w.js82ms53ms4ms3rd
C
Green Hosting
Action
Whether the site is served from green-energy infrastructure
REVIEW

Green Hosting

No green hosting detected

A+
Text Compression
All text resources are compressed
PASS
All text resources are compressed
Info::
All text resources are compressed
All text resources are properly compressed.
A+
Font Loading
4 fonts (110 KB)
PASS
4 fonts (110 KB)
Info::
4 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

4

110 KB total

Render-blocking

0

of 4

Dominant font-display

swap

Most common across fonts

Font loading timeline
Transfer FOIT (block) FOUT (swap)
0 ms 1.0 s 2.0 s 3.0 s 4.0 s 5.0 s 6.0 s FCP 3.9 s LCP 4.4 shttps://www.bnf.fr/themes/custom/bnfsi/fonts/roboto-condensed/robotocondensed-light-webfont.woff2robotocondensed-light-w... https://www.bnf.fr/themes/custom/bnfsi/fonts/roboto-condensed/robotocondensed-light-webfont.woff2 — 19.5 KiB — 930 ms — font-display: swaphttps://www.bnf.fr/themes/custom/bnfsi/fonts/roboto-condensed/robotocondensed-bold-webfont.woff2robotocondensed-bold-we... https://www.bnf.fr/themes/custom/bnfsi/fonts/roboto-condensed/robotocondensed-bold-webfont.woff2 — 19.3 KiB — 930 ms — font-display: swaphttps://www.bnf.fr/themes/custom/bnfsi/fonts/roboto-condensed/robotocondensed-regular-webfont.woff2robotocondensed-regular... https://www.bnf.fr/themes/custom/bnfsi/fonts/roboto-condensed/robotocondensed-regular-webfont.woff2 — 19.7 KiB — 931 ms — font-display: swaphttps://www.bnf.fr/themes/custom/bnfsi/fonts/GabrielaStencil/3571A5_0_0.woff23571A5_0_0.woff2 https://www.bnf.fr/themes/custom/bnfsi/fonts/GabrielaStencil/3571A5_0_0.woff2 — 51.3 KiB — 1.9 s — font-display: swap
robotocondensed-light-w... woff2 swap
Size 20 KB
Load time 930 ms
Start 3.8 s
Risk FOUT — text flashes from fallback to web font
robotocondensed-bold-we... woff2 swap
Size 19 KB
Load time 930 ms
Start 3.8 s
Risk FOUT — text flashes from fallback to web font
robotocondensed-regular... woff2 swap
Size 20 KB
Load time 931 ms
Start 3.8 s
Risk FOUT — text flashes from fallback to web font
3571A5_0_0.woff2 woff2 swap
Size 51 KB
Load time 1.9 s
Start 3.9 s
Risk FOUT — text flashes from fallback to web font
Optimization checklist
  • Preload critical fonts (priority=high)
  • Use woff2 format for all fonts
  • Set font-display to swap, optional, or fallback
  • Subset large fonts (≤100 KB each)
A+
Resource Caching
All resources properly cached
PASS
All resources properly cached
Info::
No caching issues found
All static resources have appropriate caching headers.
A+
Critical Rendering Path
No render-blocking resources
PASS
No render-blocking resources
Info::
No render-blocking resources detected
A+
Resource Hints
No optimization needed
PASS
No optimization needed
Info::
No resource hint issues
Network Waterfall
74 requests over 7073ms
INFO
0 ms 1.0 s 2.0 s 3.0 s 4.0 s 5.0 s 6.0 s 7.0 s FCP 3.9 s LCP 4.4 shttps://bnf.fr// https://bnf.fr/ — 301 — 240 B — 640 ms — http/1.1https://www.bnf.fr/www.bnf.fr/ https://www.bnf.fr/ — 301 — 263 B — 728 ms — h2https://www.bnf.fr/frwww.bnf.fr/fr https://www.bnf.fr/fr — 200 — 23.5 KiB — 1.4 s — h2https://www.bnf.fr/sites/default/files/css/css_8HI42-D1tBVDR0BvROp7shTKHWVfh4hvtwuZwRO3iL0.csswww.bnf.fr/sites/default/files/css/... https://www.bnf.fr/sites/default/files/css/css_8HI42-D1tBVDR0BvROp7shTKHWVfh4hvtwuZwRO3iL0.css — 200 — 2.1 KiB — 168 ms — h2https://www.bnf.fr/sites/default/files/css/css_60nmC-LRwuUojk0M2-39M0biKmuPbE_hywdyo-DmbEs.csswww.bnf.fr/sites/default/files/css/... https://www.bnf.fr/sites/default/files/css/css_60nmC-LRwuUojk0M2-39M0biKmuPbE_hywdyo-DmbEs.css — 200 — 95.1 KiB — 614 ms — h2https://tag.aticdn.net/18798/smarttag.jstag.aticdn.net/18798/smarttag.js https://tag.aticdn.net/18798/smarttag.js — 200 — 26.5 KiB — 22 ms — h2https://tarteaucitron.io/load.js?domain=bnf.fr/fr&uuid=91ba7c974c752a888f0a2765181efcbea3a33ef9tarteaucitron.io/load.js?domain=bnf... https://tarteaucitron.io/load.js?domain=bnf.fr/fr&uuid=91ba7c974c752a888f0a2765181efcbea3a33ef9 — 301 — 201 B — 507 ms — h2https://www.bnf.fr/sites/default/files/svg/picto_menu-burger-annotation_FR.svgwww.bnf.fr/sites/default/files/svg/... https://www.bnf.fr/sites/default/files/svg/picto_menu-burger-annotation_FR.svg — 200 — 612 B — 169 ms — h2https://www.bnf.fr/sites/default/files/svg/picto_mon-espace.svgwww.bnf.fr/sites/default/files/svg/... https://www.bnf.fr/sites/default/files/svg/picto_mon-espace.svg — 200 — 1.3 KiB — 482 ms — h2https://www.bnf.fr/sites/default/files/svg/picto_horaires-acces.svgwww.bnf.fr/sites/default/files/svg/... https://www.bnf.fr/sites/default/files/svg/picto_horaires-acces.svg — 200 — 506 B — 442 ms — h2https://www.bnf.fr/sites/default/files/svg/picto_agenda.svgwww.bnf.fr/sites/default/files/svg/... https://www.bnf.fr/sites/default/files/svg/picto_agenda.svg — 200 — 746 B — 164 ms — h2https://cdntag.tarteaucitron.io/load.js?domain=bnf.fr/fr&uuid=91ba7c974c752a888f0a2765181efcbea3a33ef9cdntag.tarteaucitron.io/load.js?dom... https://cdntag.tarteaucitron.io/load.js?domain=bnf.fr/fr&uuid=91ba7c974c752a888f0a2765181efcbea3a33ef9 — 200 — 21.9 KiB — 642 ms — h2https://www.bnf.fr/sites/default/files/svg/picto_catalogue.svgwww.bnf.fr/sites/default/files/svg/... https://www.bnf.fr/sites/default/files/svg/picto_catalogue.svg — 200 — 682 B — 163 ms — h2https://www.bnf.fr/sites/default/files/js/js_HCUq-SQK4ouQGcgWI_9vvAZpIAbwprXmQrtwZH11Z4w.jswww.bnf.fr/sites/default/files/js/j... https://www.bnf.fr/sites/default/files/js/js_HCUq-SQK4ouQGcgWI_9vvAZpIAbwprXmQrtwZH11Z4w.js — 200 — 43.1 KiB — 166 ms — h2https://www.bnf.fr/sites/default/files/js/js_ogHJM-y5BPuXvT1_XF46lI_uNY5jd0mbO_CLaUb3JOs.jswww.bnf.fr/sites/default/files/js/j... https://www.bnf.fr/sites/default/files/js/js_ogHJM-y5BPuXvT1_XF46lI_uNY5jd0mbO_CLaUb3JOs.js — 200 — 240.9 KiB — 475 ms — h2https://www.bnf.fr/sites/default/files/svg/picto_inscription-billeterie.svgwww.bnf.fr/sites/default/files/svg/... https://www.bnf.fr/sites/default/files/svg/picto_inscription-billeterie.svg — 200 — 855 B — 162 ms — h2https://www.bnf.fr/sites/default/files/inline-images/sidebar_nav_close.pngwww.bnf.fr/sites/default/files/inli... https://www.bnf.fr/sites/default/files/inline-images/sidebar_nav_close.png — 200 — 1.6 KiB — 177 ms — h2https://www.bnf.fr/sites/default/files/inline-images/sidebar_nav_logo.pngwww.bnf.fr/sites/default/files/inli... https://www.bnf.fr/sites/default/files/inline-images/sidebar_nav_logo.png — 200 — 8.1 KiB — 177 ms — h2https://www.bnf.fr/sites/default/files/logo.svgwww.bnf.fr/sites/default/files/logo... https://www.bnf.fr/sites/default/files/logo.svg — 200 — 1.4 KiB — 179 ms — h2https://www.bnf.fr/themes/custom/bnfsi/images/svg/picto_loupe.svgwww.bnf.fr/themes/custom/bnfsi/imag... https://www.bnf.fr/themes/custom/bnfsi/images/svg/picto_loupe.svg — 200 — 412 B — 174 ms — h2https://www.bnf.fr/sites/default/files/styles/header_big_height/public/2021-11/jardin_fm_automne.jpg?h=5a47b365&itok=zbkCSqDOwww.bnf.fr/sites/default/files/styl... https://www.bnf.fr/sites/default/files/styles/header_big_height/public/2021-11/jardin_fm_automne.jpg?h=5a47b365&itok=zbkCSqDO — 200 — 448.4 KiB — 965 ms — h2https://www.bnf.fr/sites/default/files/styles/mea_1_home/public/2026-03/Expo_cartes_imaginaires.jpg?h=06ac0d8c&itok=rGMohZTswww.bnf.fr/sites/default/files/styl... https://www.bnf.fr/sites/default/files/styles/mea_1_home/public/2026-03/Expo_cartes_imaginaires.jpg?h=06ac0d8c&itok=rGMohZTs — 200 — 104.7 KiB — 341 ms — h2https://www.bnf.fr/sites/default/files/styles/slider_1_all/public/2025-04/visite-musee.jpg?h=10d202d3&itok=BRBENPYtwww.bnf.fr/sites/default/files/styl... 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5.8 KiB — 159 ms — h2https://cdn.tarteaucitron.io/lang/tarteaucitron.fr.min.js?v=1.32.0cdn.tarteaucitron.io/lang/tarteauci... https://cdn.tarteaucitron.io/lang/tarteaucitron.fr.min.js?v=1.32.0 — 200 — 1.8 KiB — 159 ms — h2https://www.bnf.fr/themes/custom/bnfsi/favicon.icowww.bnf.fr/themes/custom/bnfsi/favi... https://www.bnf.fr/themes/custom/bnfsi/favicon.ico — 200 — 279 B — 163 ms — h2https://cdn.tarteaucitron.io/tarteaucitron.services.min.js?v=1.32.0cdn.tarteaucitron.io/tarteaucitron.... https://cdn.tarteaucitron.io/tarteaucitron.services.min.js?v=1.32.0 — 200 — 36.0 KiB — 161 ms — h2data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAHcAAAAeCAYAAAAWwoEYAAADl0lEQVRoge1Y0W3bQAx9CjKARlC+9…data:image/png;base64,iVBORw0KGgoAA... data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAHcAAAAeCAYAAAAWwoEYAAADl0lEQVRoge1Y0W3bQAx9CjKARlC+9… — 200 — 0 B — 0 ms — datadata:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAADIAAAAyCAYAAAAeP4ixAAAGA0lEQVRoge1a207bWBRdBtJwLYZhK…data:image/png;base64,iVBORw0KGgoAA... 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HTML JavaScript CSS Images Fonts XHR/Fetch Other
Third-Party Script Cost
Per-script blocking time, transfer cost, and cache headers
INFO
100% of JavaScript execution is third-party
First-party Third-party 747ms · 308KB · €3/mo
www.bnf.fr
Other
Costly
Execution 373ms
Transfer 24 KB
Monthly Cost €2/mo
www.bnf.fr
Other
Optional
Execution 147ms
Transfer 241 KB
Unused 80%
Monthly Cost €1/mo
Unattributable
Other
Optional
Execution 144ms
Transfer 0 KB
Monthly Cost €1/mo
www.bnf.fr
Other
Optional
Execution 82ms
Transfer 43 KB
Monthly Cost €0/mo

These scripts may cost more than they're worth

  • www.bnf.fr adds 373ms and costs ~€2/month

100% of JavaScript execution time is spent on third-party scripts. Consider auditing which scripts are essential.

Why this matters

When third-party JS execution time exceeds your own, performance gains from frontend work are capped by code you don't own.

Learn more ▾

Every millisecond of third-party JS competes with your own for main-thread time. If their share is bigger than yours, optimization on your code base barely moves the needle. Audit, defer, or remove third-parties before further frontend optimization. Use Lighthouse's third-party audit to identify the worst offenders.

Source: web.dev

www.bnf.fr takes 373ms of CPU time. Consider loading it asynchronously or replacing it with a lighter alternative.

Why this matters

This script has high main-thread execution time — optimize hot paths or defer.

Source: web.dev

80% of www.bnf.fr's code is unused. The script may be loading features you don't use.

Why this matters

Bundle has high unused-code ratio — tree-shaking and route-splitting recover the wasted bytes.

Source: web.dev

How third-party costs are calculated

All checks on this page are automated. Results are estimates - run targeted manual reviews when the score affects a release decision.

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