Performance
· 15 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.Performance-focused optimization plan with CWV assessment, top offenders, and time estimates
First Contentful Paint First Contentful Paint — how long until the browser renders the first piece of content. Under 1.8s is good.
1.79 s
Largest Contentful Paint Largest Contentful Paint — how long until the largest visible element loads. Under 2.5s is good.
2.36 s
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.
0.003
Speed Index Speed Index — how quickly content is visually displayed during load. Under 3.4s is good.
2.29 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.
2.36 s
Page Load Progression
FPage Weight BudgetAction3.3 MB transferred, 115 requestsFIX
Convert images to WebP/AVIF and resize to display dimensions to reduce transfer size.
Image bandwidth is high — modern formats (WebP/AVIF) and resizing typically cut it 50%+.
Source: web.dev
Large JavaScript bundles delay interactivity. Split code by route or defer non-critical scripts.
JavaScript bundle is large — code-split routes and lazy-load off-screen components to defer.
Source: web.dev
Each request adds latency. Bundle small files, use sprites, or eliminate unnecessary requests.
High HTTP request count — bundling, sprite-ing, and HTTP/2 server push can reduce per-request overhead.
Source: web.dev
DThird-Party ImpactAction100% third-party, 0 ms blockingFIX
DPage Weight InventoryAction115 resources · 3.3 MB · 200 KB savings availableFIX
~199.5 KiB of savings available
| # | Resource | Type | Size | Cache | Unused | 3rd party | Issues |
|---|---|---|---|---|---|---|---|
| — | — | ||||||
| 115 resources | 3.3 MiB | ||||||
FHTTP CachingActionNo cache headersFIX
No Cache-Control header
Adding a Cache-Control header can significantly improve repeat-visit performance.
CImage OptimizationAction68 images, 0 KB saveableREVIEW
Set explicit width and height to prevent CLS.
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.
Performance issues directly impact user engagement and conversion rates.
BJS Execution Cost552ms total JS executionREVIEW
Main Thread Breakdown
| Script | Total | Scripting | Parse/Compile | Party |
|---|---|---|---|---|
| https://www.iarc.who.int/ | 183ms | 27ms | 1ms | 3rd |
| Unattributable | 159ms | 2ms | 0ms | 3rd |
| https://www.iarc.who.int/wp-content/themes/iarc-theme-new/js/jquery-3.3.1.min.js?ver=5.3.2 | 130ms | 84ms | 2ms | 3rd |
| https://www.googletagmanager.com/gtag/js?id=G-END57GKPMR | 80ms | 61ms | 16ms | 3rd |
CJS BundlesAction22 scripts, 200 KB unusedREVIEW
Downloaded but never executed on this page.
| Script | Size | Unused | Minified | Party |
|---|---|---|---|---|
| https://www.googletagmanager.com/gtm.js?id=GTM-PQ9TBQ4 | 132 KB | 73 KB (55%) | ✓ | 3rd |
| https://www.googletagmanager.com/gtag/js?id=G-END57GKPMR | 158 KB | 66 KB (42%) | ✓ | 3rd |
| https://www.iarc.who.int/wp-content/themes/iarc-theme-new/js/swiper.min.js?ver=5.3.2 | 39 KB | 34 KB (88%) | ✓ | 3rd |
| https://www.iarc.who.int/wp-includes/js/jquery/jquery.js?ver=1.12.4-wp | 39 KB | 26 KB (68%) | ✓ | 3rd |
| https://www.iarc.who.int/wp-content/themes/iarc-theme-new/js/popper.min.js?ver=5.3.2 | 8 KB | — | ✓ | 3rd |
| https://www.iarc.who.int/wp-includes/js/jquery/jquery-migrate.min.js?ver=1.4.1 | 5 KB | — | ✓ | 3rd |
| https://www.iarc.who.int/wp-content/themes/iarc-theme-new/js/skip-link-focus-fix.js?ver=20151215 | 1 KB | — | ✓ | 3rd |
| https://www.iarc.who.int/wp-content/themes/iarc-theme-new/js/chosen.min.js?ver=5.3.2 | 8 KB | — | ✓ | 3rd |
| https://www.iarc.who.int/wp-content/themes/iarc-theme-new/js/mCustomScrollbar.min.js?ver=5.3.2 | 14 KB | — | ✓ | 3rd |
| https://www.iarc.who.int/wp-content/themes/iarc-theme-new/js/tether.min.js?ver=5.3.2 | 9 KB | — | ✓ | 3rd |
Consider code splitting or tree shaking to reduce unused code.
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.
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.
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.
This bundle has high unused code — code-split or tree-shake to ship only what executes.
Source: web.dev / Lighthouse coverage
CGreen HostingActionWhether the site is served from green-energy infrastructureREVIEW
Green Hosting
No green hosting detected
A+Text CompressionAll text resources are compressedPASS
A+Font Loading3 fonts (101 KB)PASS
Web fonts
3
101 KB total
Render-blocking
0
of 3
Dominant font-display
swap
Most common across fonts
Font loading timeline
- Convert to woff2 for ~30% smaller file size
- Convert to woff2 for ~30% smaller file size
- Convert to woff2 for ~30% smaller file size
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)
Fixing the unchecked items could save ~30 KB and ~60 ms
A+Resource CachingAll resources properly cachedPASS
A+Critical Rendering PathNo render-blocking resourcesPASS
A+Resource HintsNo optimization neededPASS
Network Waterfall115 requests over 2246msINFO
Third-Party Script CostPer-script blocking time, transfer cost, and cache headersINFO
| Script | Category | Execution | Transfer | Unused | Monthly Cost | Verdict |
|---|---|---|---|---|---|---|
www.iarc.who.int www.iarc.who.int | Other | 183ms | 19 KB | — | €2/mo | Optional |
Unattributable Unattributable | Other | 159ms | 0 KB | — | €2/mo | Optional |
www.iarc.who.int www.iarc.who.int | Other | 130ms | 35 KB | — | €1/mo | Optional |
Google Tag Manager www.googletagmanager.com | Tag Manager | 80ms | 158 KB | 42% | €1/mo | Optional |
100% of JavaScript execution time is spent on third-party scripts. Consider auditing which scripts are essential.
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