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.
666 ms
Largest Contentful Paint Largest Contentful Paint — how long until the largest visible element loads. Under 2.5s is good.
1.75 s
Total Blocking Time Total Blocking Time — total time the main thread was blocked, preventing user input. Under 200ms is good.
26 ms
Cumulative Layout Shift Cumulative Layout Shift — measures visual stability. How much the page layout shifts during loading. Under 0.1 is good.
0.072
Speed Index Speed Index — how quickly content is visually displayed during load. Under 3.4s is good.
1.08 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.
1.75 s
Page Load Progression
375 ms
750 ms
1.1 s
1.5 s 1.9 s 2.2 s 2.6 s 3.0 sDPage Weight BudgetAction2.1 MB transferred, 57 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
Subset fonts to include only used characters, or switch to system font stacks.
Font payload is large — subset to used glyphs only, or fall back to system fonts (zero load time).
Source: web.dev font loading
DThird-Party ImpactAction100% third-party, 0 ms blockingFIX
DPage Weight InventoryAction57 resources · 2.1 MB · 75 KB savings availableFIX
~75.4 KiB of savings available
| # | Resource | Type | Size | Cache | Unused | 3rd party | Issues |
|---|---|---|---|---|---|---|---|
| — | — | ||||||
| 57 resources | 2.1 MiB | ||||||
FHTTP CachingActionNo cache headersFIX
No Cache-Control header
Adding a Cache-Control header can significantly improve repeat-visit performance.
BJS Execution Cost505ms total JS executionREVIEW
Main Thread Breakdown
| Script | Total | Scripting | Parse/Compile | Party |
|---|---|---|---|---|
| https://consent.cookiebot.eu/376e78a0-37fc-48a7-9d73-a58eb8a9c2af/cc.js?renew=false&referer=www.tudelft.nl&dnt=false&init=false&culture=nl | 154ms | 62ms | 11ms | 3rd |
| https://www.tudelft.nl/ | 141ms | 6ms | 3ms | 3rd |
| https://www.tudelft.nl/_assets/f6b877d73456607fbfa2de3e3c5fd420/JavaScript/dist.javascripts.350f3e01aa.min.js?1776230288 | 113ms | 67ms | 8ms | 3rd |
| Unattributable | 98ms | 4ms | 0ms | 3rd |
BJS Bundles12 scripts, 75 KB unusedREVIEW
Downloaded but never executed on this page.
| Script | Size | Unused | Minified | Party |
|---|---|---|---|---|
| https://www.tudelft.nl/_assets/f6b877d73456607fbfa2de3e3c5fd420/JavaScript/dist.javascripts.350f3e01aa.min.js?1776230288 | 116 KB | 75 KB (65%) | ✓ | 3rd |
| https://www.tudelft.nl/typo3temp/assets/js/222a0289ea16d2c543939f3cf084853a.js?1776230457 | 1 KB | — | ✓ | 3rd |
| https://siteimproveanalytics.com/js/siteanalyze_6005654.js | 40 KB | — | ✓ | 3rd |
| https://consent.cookiebot.eu/uc.js | 30 KB | — | ✓ | 3rd |
| https://consent.cookiebot.eu/376e78a0-37fc-48a7-9d73-a58eb8a9c2af/cc.js?renew=false&referer=www.tudelft.nl&dnt=false&init=false&culture=nl | 92 KB | — | ✓ | 3rd |
| https://www.browsealoud.com/plus/scripts/3.1.0/ba.js | 2 KB | — | ✓ | 3rd |
| https://plus.browsealoud.com/js/urlinfo/www.tudelft.nl.js | 1 KB | — | ✓ | 3rd |
| https://www.browsealoud.com/modules/3.11.0/browsealoud.js | 41 KB | — | ✓ | 3rd |
| https://plus.browsealoud.com/js/urlinfo/www.tudelft.nl.js | 0 KB | — | ✓ | 3rd |
| https://www.browsealoud.com/modules/3.11.0/4916.dd13ed0cd26117b33f9d.js | 30 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
CGreen HostingActionWhether the site is served from green-energy infrastructureREVIEW
Green Hosting
No green hosting detected
A+Text CompressionAll text resources are compressedPASS
AImage Optimization30 images, 0 KB saveablePASS
A+Font Loading4 fonts (221 KB)PASS
Web fonts
4
221 KB total
Render-blocking
0
of 4
Dominant font-display
swap
Most common across fonts
Font loading timeline
- 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 ~3 KB and ~6 ms
A+Resource CachingAll resources properly cachedPASS
A+Critical Rendering PathNo render-blocking resourcesPASS
A+Resource HintsNo optimization neededPASS
Network Waterfall57 requests over 1493msINFO
Third-Party Script CostPer-script blocking time, transfer cost, and cache headersINFO
| Script | Category | Execution | Transfer | Unused | Monthly Cost | Verdict |
|---|---|---|---|---|---|---|
consent.cookiebot.eu consent.cookiebot.eu | Other | 154ms | 92 KB | — | €2/mo | Optional |
www.tudelft.nl www.tudelft.nl | Other | 141ms | 33 KB | — | €2/mo | Optional |
www.tudelft.nl www.tudelft.nl | Other | 113ms | 116 KB | 65% | €1/mo | Optional |
Unattributable Unattributable | Other | 98ms | 0 KB | — | €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
65% of www.tudelft.nl's code is unused. The script may be loading features you don't use.
Bundle has high unused-code ratio — tree-shaking and route-splitting recover the wasted bytes.
Source: web.dev