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https://royalsociety.org

Performance

· 15 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
84
GRADE
B
FIX
2
REVIEW
3
PASS
8
INFO
2

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

Mobile Desktop
99
Performance Overall performance score (0–100) based on Core Web Vitals and other metrics. 90+ is good.
95
Accessibility Measures how accessible the page is for users with disabilities. Checks color contrast, ARIA labels, and semantic HTML.
96
Best Practices Checks for modern web development best practices including HTTPS, no console errors, and secure JavaScript.
92
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.

478 ms

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

478 ms

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

0 ms

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

0.000

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

1.18 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.

478 ms

Page Load Progression

375 ms
750 ms
1.1 s
1.5 s
1.9 s
2.2 s
2.6 s
3.0 s
Checks
15
8 PASS 3 REVIEW 2 FIX
D
Third-Party Impact
Action
75% third-party, 0 ms blocking
FIX
75% third-party, 0 ms blocking
Warning::
Third-party code accounts for 75% of page weight (341.8 KiB of 453.9 KiB)
Info::
Third-party blocking time is low (0 ms)
25%
75%
First-party Third-party
D
HTTP Caching
Action
no-store (uncacheable)
FIX
no-store (uncacheable)
Info::
Cache-Control: no-store prevents all caching
Intentional for dynamic content, but increases server load for every page view.
Got: no-cache, no-store
Info::
No ETag or Last-Modified header
Conditional requests (304 Not Modified) are not possible without validators.
Cache-Control

no-cache, no-store

DirectiveValueMeaning
no-cache—Cache but always revalidate first
no-store—Never cache this response
C
Image Optimization
Action
7 images, 0 KB saveable
REVIEW
7 images, 0 KB saveable
Warning::
https://royalsociety.org/-/media/science-book-priz... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://royalsociety.org/url(/-/media/navigation/f... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://royalsociety.org/assets/images/logo@2x.png is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
7 images 28 KB
0 oversized -0 KB
6 legacy format
4 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

Performance issues directly impact user engagement and conversion rates.

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 Bundles
6 scripts, 138 KB unused
REVIEW
6 scripts, 138 KB unused
Warning::
https://www.googletagmanager.com/gtm.js?id=GTM-NS6...: 84 KB unused (50%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://cdn-ukwest.onetrust.com/scripttemplates/20...: 55 KB unused (52%)
Consider code splitting or tree shaking to reduce unused code.
Info::
Total unused JavaScript: 138 KB
138 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://www.googletagmanager.com/gtm.js?id=GTM-NS67FDG169 KB84 KB (50%)✓3rd
https://cdn-ukwest.onetrust.com/scripttemplates/202401.2.0/otBannerSdk.js105 KB55 KB (52%)✓3rd
https://royalsociety.org/assets/js/main.js0 KB—✓1st
https://cdn-ukwest.onetrust.com/scripttemplates/otSDKStub.js9 KB—✓3rd
https://cdn-ukwest.onetrust.com/consent/c343a84c-eec8-4e9a-a16b-69278300c712/c343a84c-eec8-4e9a-a16b-69278300c712.json2 KB—✓3rd
https://cdn-ukwest.onetrust.com/consent/c343a84c-eec8-4e9a-a16b-69278300c712/018dd5ec-e5d8-7fa4-9da4-b7f3f6c5b33f/en.json15 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

C
Green Hosting
Action
Whether the site is served from green-energy infrastructure
REVIEW

Green Hosting

No green hosting detected

A+
Page Weight Budget
454 KB transferred, 23 requests
PASS
454 KB transferred, 23 requests
Info::
Page weighs 1.2 MB (454 KB transferred)
Info::
23 HTTP requests
Info::
Estimated 0.09 g CO2 per page load
454 KB / 2.4 MB budget
454 KB transferred
23 requests
0.09 g CO2 per page load
JavaScript 282.8 KiB 62%
HTML 100.3 KiB 22%
Other 35.0 KiB 8%
Images 28.2 KiB 6%
Other 5.1 KiB 1%
Other 2.3 KiB 1%
CSS 164 B 0%
0 2.4 MB 4.9 MB
Under budget
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+
JS Execution Cost
127ms total JS execution
PASS
127ms total JS execution
Info::
https://www.googletagmanager.com/gtm.js?id=GTM-NS6...: 73ms CPU time
Info::
Unattributable: 54ms CPU time
Warning::
Third-party scripts: 127ms (100% of total)

Main Thread Breakdown

Script Evaluation 50% Other 23% Style & Layout 12% Script Parsing & Compilation 9% Parse HTML & CSS 4%
ScriptTotalScriptingParse/CompileParty
https://www.googletagmanager.com/gtm.js?id=GTM-NS67FDG73ms59ms10ms3rd
Unattributable54ms17ms0ms3rd
A+
Font Loading
No web fonts (system fonts)
PASS
No web fonts (system fonts)
Info::
No web fonts loaded — system fonts are fastest
No web fonts loaded — system fonts are optimal.
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
A
Page Weight Inventory
23 resources · 454 KB · 138 KB savings available
PASS
23 resources · 454 KB · 138 KB savings available
Info::
Within 1MB page-weight target
Got: 454 KB
Info::
~138 KB of savings available
Warning::
12 third-party resources (75% of weight)
23 resources · 453.9 KiB · 12 third-party Within 1MB page-weight target
JavaScript 66% · 299.6 KiB
Document 23% · 105.4 KiB
Image 6% · 28.7 KiB
Other 4% · 16.2 KiB
CSS 1% · 4.0 KiB

~138.4 KiB of savings available

Remove unused JavaScript: 138.4 KiB
Network Waterfall
23 requests over 891ms
INFO
0 ms 200 ms 400 ms 600 ms 800 ms FCP 478 ms LCP 478 mshttps://royalsociety.org// https://royalsociety.org/ — 200 — 100.3 KiB — 190 ms — h2https://royalsociety.org/assets/css/main.css/assets/css/main.css https://royalsociety.org/assets/css/main.css — 403 — 82 B — 44 ms — h2https://royalsociety.org/assets/css/custom.css/assets/css/custom.css https://royalsociety.org/assets/css/custom.css — 403 — 82 B — 44 ms — h2https://royalsociety.org/assets/images/logo@2x.png/assets/images/logo@2x.png https://royalsociety.org/assets/images/logo@2x.png — 403 — 1.6 KiB — 44 ms — h2https://royalsociety.org/-/media/science-book-prize/ypbp/2025/winner-2025-ypbp-ceremony.jpg/-/media/science-book-prize/ypbp/20... https://royalsociety.org/-/media/science-book-prize/ypbp/2025/winner-2025-ypbp-ceremony.jpg — 403 — 1.6 KiB — 30 ms — h2https://royalsociety.org/url(/-/media/navigation/footer/logoalt2x.png);/url(/-/media/navigation/footer/log... https://royalsociety.org/url(/-/media/navigation/footer/logoalt2x.png); — 403 — 1.6 KiB — 30 ms — h2https://royalsociety.org/assets/js/main.js/assets/js/main.js https://royalsociety.org/assets/js/main.js — 403 — 82 B — 29 ms — h2https://royalsociety.org/-/media/current-topics/des8801_website-transformation-project_images_new-technologies.jpg/-/media/current-topics/des8801_web... https://royalsociety.org/-/media/current-topics/des8801_website-transformation-project_images_new-technologies.jpg — 403 — 1.6 KiB — 29 ms — h2https://www.googletagmanager.com/gtm.js?id=GTM-NS67FDGwww.googletagmanager.com/gtm.js?id=... https://www.googletagmanager.com/gtm.js?id=GTM-NS67FDG — 200 — 169.2 KiB — 175 ms — h2https://cdn-ukwest.onetrust.com/scripttemplates/otSDKStub.jscdn-ukwest.onetrust.com/scripttempl... https://cdn-ukwest.onetrust.com/scripttemplates/otSDKStub.js — 200 — 9.1 KiB — 68 ms — h2https://cdn-ukwest.onetrust.com/consent/c343a84c-eec8-4e9a-a16b-69278300c712/c343a84c-eec8-4e9a-a16b-69278300c712.jsoncdn-ukwest.onetrust.com/consent/c34... https://cdn-ukwest.onetrust.com/consent/c343a84c-eec8-4e9a-a16b-69278300c712/c343a84c-eec8-4e9a-a16b-69278300c712.json — 200 — 2.1 KiB — 83 ms — h2https://royalsociety.org/assets/icons/favicon-32x32.png/assets/icons/favicon-32x32.png https://royalsociety.org/assets/icons/favicon-32x32.png — 403 — 1.7 KiB — 27 ms — h2https://royalsociety.org/assets/icons/favicon-16x16.png/assets/icons/favicon-16x16.png https://royalsociety.org/assets/icons/favicon-16x16.png — 403 — 1.7 KiB — 27 ms — h2https://royalsociety.org/assets/icons/android-chrome-192x192.png/assets/icons/android-chrome-192x19... https://royalsociety.org/assets/icons/android-chrome-192x192.png — 403 — 1.7 KiB — 28 ms — h2https://geolocation.onetrust.com/cookieconsentpub/v1/geo/locationgeolocation.onetrust.com/cookiecons... https://geolocation.onetrust.com/cookieconsentpub/v1/geo/location — 200 — 203 B — 31 ms — h2https://cdn-ukwest.onetrust.com/scripttemplates/202401.2.0/otBannerSdk.jscdn-ukwest.onetrust.com/scripttempl... https://cdn-ukwest.onetrust.com/scripttemplates/202401.2.0/otBannerSdk.js — 200 — 104.5 KiB — 49 ms — h2https://cdn-ukwest.onetrust.com/consent/c343a84c-eec8-4e9a-a16b-69278300c712/018dd5ec-e5d8-7fa4-9da4-b7f3f6c5b33f/en.jsoncdn-ukwest.onetrust.com/consent/c34... https://cdn-ukwest.onetrust.com/consent/c343a84c-eec8-4e9a-a16b-69278300c712/018dd5ec-e5d8-7fa4-9da4-b7f3f6c5b33f/en.json — 200 — 14.7 KiB — 48 ms — h2https://cdn-ukwest.onetrust.com/scripttemplates/202401.2.0/assets/otFlat.jsoncdn-ukwest.onetrust.com/scripttempl... https://cdn-ukwest.onetrust.com/scripttemplates/202401.2.0/assets/otFlat.json — 200 — 3.3 KiB — 33 ms — h2https://cdn-ukwest.onetrust.com/scripttemplates/202401.2.0/assets/v2/otPcPanel.jsoncdn-ukwest.onetrust.com/scripttempl... https://cdn-ukwest.onetrust.com/scripttemplates/202401.2.0/assets/v2/otPcPanel.json — 200 — 12.7 KiB — 34 ms — h2https://cdn-ukwest.onetrust.com/scripttemplates/202401.2.0/assets/otCommonStyles.csscdn-ukwest.onetrust.com/scripttempl... https://cdn-ukwest.onetrust.com/scripttemplates/202401.2.0/assets/otCommonStyles.css — 200 — 3.9 KiB — 35 ms — h2https://cdn-ukwest.onetrust.com/logos/static/ot_guard_logo.svgcdn-ukwest.onetrust.com/logos/stati... https://cdn-ukwest.onetrust.com/logos/static/ot_guard_logo.svg — 200 — 488 B — 32 ms — h2https://cdn-ukwest.onetrust.com/logos/static/ot_company_logo.pngcdn-ukwest.onetrust.com/logos/stati... https://cdn-ukwest.onetrust.com/logos/static/ot_company_logo.png — 200 — 19.2 KiB — 29 ms — h2https://cdn-ukwest.onetrust.com/logos/static/powered_by_logo.svgcdn-ukwest.onetrust.com/logos/stati... https://cdn-ukwest.onetrust.com/logos/static/powered_by_logo.svg — 200 — 2.6 KiB — 30 ms — h2
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 127ms · 169KB · $2/mo
Google Tag Manager
Tag Manager
Optional
Execution 73ms
Transfer 169 KB
Unused 50%
Monthly Cost $1/mo
Unattributable
Other
Optional
Execution 54ms
Transfer 0 KB
Monthly Cost $1/mo

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

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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