Performance
· 26 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.
5.58 s
Largest Contentful Paint Largest Contentful Paint — how long until the largest visible element loads. Under 2.5s is good.
6.40 s
Total Blocking Time Total Blocking Time — total time the main thread was blocked, preventing user input. Under 200ms is good.
1.69 s
Cumulative Layout Shift Cumulative Layout Shift — measures visual stability. How much the page layout shifts during loading. Under 0.1 is good.
0.113
Speed Index Speed Index — how quickly content is visually displayed during load. Under 3.4s is good.
10.46 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.
30.94 s
Page Load Progression
FPage Weight BudgetAction4.8 MB transferred, 83 requestsFIX
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
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
FJS Execution CostAction7049ms total JS executionFIX
Main Thread Breakdown
| Script | Total | Scripting | Parse/Compile | Party |
|---|---|---|---|---|
| https://www.stib-mivb.be/modules/stibmivb-template/javascript/main-rrfkY9Wl.js | 1875ms | 1177ms | 440ms | 3rd |
| https://www.stib-mivb.be/home | 1228ms | 10ms | 3ms | 3rd |
| Unattributable | 1094ms | 75ms | 0ms | 3rd |
| https://tracking.stib-mivb.be/gtm.js?id=GTM-NR8C6F27>m_auth=g3wZAhZGvfleAd4TmVXo8g&>m_preview=env-1>m_cookies_win=x | 618ms | 516ms | 91ms | 3rd |
| https://www.stib-mivb.be/modules/stibmivb-template/javascript/vendors.js | 546ms | 23ms | 501ms | 3rd |
| https://www.googletagmanager.com/gtag/js?id=AW-875372945&cx=c>m=4e6562&sign=e4fb3875ec5d019937d5aa3bc6c53afd87a2e02bace230b3e281cd79c9e60c94_20260510 | 328ms | 275ms | 49ms | 3rd |
| https://connect.facebook.net/signals/config/537872945975515?v=2.9.313&r=stable&domain=www.stib-mivb.be&hme=97937018cefade17726f0472876fc101316b2ce9008a35a6a5a7977d7436151a&ex_m=104%2C205%2C154%2C22%2C72%2C73%2C145%2C68%2C67%2C11%2C162%2C90%2C16%2C138%2C48%2C146%2C77%2C112%2C47%2C127%2C39%2C75%2C78%2C134%2C159%2C164%2C8%2C4%2C5%2C7%2C6%2C3%2C91%2C101%2C165%2C170%2C219%2C62%2C186%2C187%2C55%2C276%2C30%2C74%2C231%2C230%2C229%2C23%2C33%2C103%2C61%2C10%2C63%2C97%2C98%2C99%2C105%2C130%2C31%2C29%2C132%2C133%2C129%2C128%2C155%2C76%2C158%2C156%2C157%2C50%2C60%2C123%2C15%2C161%2C45%2C263%2C264%2C262%2C26%2C27%2C28%2C18%2C20%2C44%2C40%2C42%2C41%2C83%2C92%2C96%2C110%2C144%2C147%2C46%2C111%2C24%2C21%2C119%2C69%2C36%2C149%2C148%2C150%2C141%2C139%2C25%2C35%2C59%2C109%2C160%2C70%2C17%2C152%2C114%2C81%2C66%2C19%2C85%2C86%2C116%2C84%2C136%2C135%2C34%2C278%2C293%2C212%2C201%2C202%2C200%2C296%2C288%2C52%2C213%2C107%2C131%2C80%2C121%2C54%2C49%2C113%2C120%2C126%2C58%2C64%2C151%2C115%2C37%2C32%2C53%2C56%2C100%2C163%2C1%2C124%2C14%2C122%2C12%2C2%2C57%2C93%2C65%2C118%2C89%2C88%2C166%2C167%2C94%2C95%2C9%2C125%2C102%2C51%2C142%2C87%2C79%2C71%2C117%2C106%2C43%2C143%2C0%2C82%2C137%2C140%2C153%2C38%2C108%2C13%2C168 | 300ms | 248ms | 50ms | 3rd |
| https://consent.cookiebot.com/uc.js | 287ms | 250ms | 15ms | 3rd |
| https://www.googletagmanager.com/gtag/js?id=DC-4708247&cx=c>m=4e6562&sign=e4fb3875ec5d019937d5aa3bc6c53afd87a2e02bace230b3e281cd79c9e60c94_20260510 | 220ms | 162ms | 54ms | 3rd |
| https://tracking.stib-mivb.be/gtag/js?id=G-XXXXXXXXXX&cx=c>m=4e6562&sign=e4fb3875ec5d019937d5aa3bc6c53afd87a2e02bace230b3e281cd79c9e60c94_20260510 | 216ms | 161ms | 54ms | 3rd |
Showing top 10 of 13 scripts
FJS BundlesAction23 scripts, 2.9 MB unusedFIX
Downloaded but never executed on this page.
| Script | Size | Unused | Minified | Party |
|---|---|---|---|---|
| https://www.stib-mivb.be/modules/stibmivb-template/javascript/vendors.js | 0 KB | 681 KB (70%) | ✗ | 3rd |
| https://www.stib-mivb.be/modules/stibmivb-template/javascript/vendors.js | 972 KB | 681 KB (70%) | ✗ | 3rd |
| https://www.stib-mivb.be/modules/stibmivb-template/javascript/main-rrfkY9Wl.js | 0 KB | 538 KB (49%) | ✓ | 3rd |
| https://www.stib-mivb.be/modules/stibmivb-template/javascript/main-rrfkY9Wl.js | 1110 KB | 538 KB (49%) | ✓ | 3rd |
| https://tracking.stib-mivb.be/gtag/js?id=G-XXXXXXXXXX&cx=c>m=4e6562&sign=e4fb3875ec5d019937d5aa3bc6c53afd87a2e02bace230b3e281cd79c9e60c94_20260510 | 381 KB | 196 KB (51%) | ✓ | 3rd |
| https://tracking.stib-mivb.be/gtm.js?id=GTM-NR8C6F27>m_auth=g3wZAhZGvfleAd4TmVXo8g&>m_preview=env-1>m_cookies_win=x | 534 KB | 190 KB (36%) | ✓ | 3rd |
| https://www.googletagmanager.com/gtag/js?id=DC-4708247&cx=c>m=4e6562&sign=e4fb3875ec5d019937d5aa3bc6c53afd87a2e02bace230b3e281cd79c9e60c94_20260510 | 130 KB | 60 KB (46%) | ✓ | 3rd |
| https://www.googletagmanager.com/gtag/js?id=AW-875372945&cx=c>m=4e6562&sign=e4fb3875ec5d019937d5aa3bc6c53afd87a2e02bace230b3e281cd79c9e60c94_20260510 | 145 KB | 53 KB (36%) | ✓ | 3rd |
| https://connect.facebook.net/signals/config/537872945975515?v=2.9.313&r=stable&domain=www.stib-mivb.be&hme=97937018cefade17726f0472876fc101316b2ce9008a35a6a5a7977d7436151a&ex_m=104%2C205%2C154%2C22%2C72%2C73%2C145%2C68%2C67%2C11%2C162%2C90%2C16%2C138%2C48%2C146%2C77%2C112%2C47%2C127%2C39%2C75%2C78%2C134%2C159%2C164%2C8%2C4%2C5%2C7%2C6%2C3%2C91%2C101%2C165%2C170%2C219%2C62%2C186%2C187%2C55%2C276%2C30%2C74%2C231%2C230%2C229%2C23%2C33%2C103%2C61%2C10%2C63%2C97%2C98%2C99%2C105%2C130%2C31%2C29%2C132%2C133%2C129%2C128%2C155%2C76%2C158%2C156%2C157%2C50%2C60%2C123%2C15%2C161%2C45%2C263%2C264%2C262%2C26%2C27%2C28%2C18%2C20%2C44%2C40%2C42%2C41%2C83%2C92%2C96%2C110%2C144%2C147%2C46%2C111%2C24%2C21%2C119%2C69%2C36%2C149%2C148%2C150%2C141%2C139%2C25%2C35%2C59%2C109%2C160%2C70%2C17%2C152%2C114%2C81%2C66%2C19%2C85%2C86%2C116%2C84%2C136%2C135%2C34%2C278%2C293%2C212%2C201%2C202%2C200%2C296%2C288%2C52%2C213%2C107%2C131%2C80%2C121%2C54%2C49%2C113%2C120%2C126%2C58%2C64%2C151%2C115%2C37%2C32%2C53%2C56%2C100%2C163%2C1%2C124%2C14%2C122%2C12%2C2%2C57%2C93%2C65%2C118%2C89%2C88%2C166%2C167%2C94%2C95%2C9%2C125%2C102%2C51%2C142%2C87%2C79%2C71%2C117%2C106%2C43%2C143%2C0%2C82%2C137%2C140%2C153%2C38%2C108%2C13%2C168 | 125 KB | 35 KB (28%) | ✓ | 3rd |
| https://connect.facebook.net/en_US/fbevents.js | 97 KB | 35 KB (36%) | ✓ | 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
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
FPage Weight InventoryAction83 resources · 4.8 MB · 2.9 MB savings availableFIX
~2.9 MiB of savings available
| # | Resource | Type | Size | Cache | Unused | 3rd party | Issues |
|---|---|---|---|---|---|---|---|
| — | — | ||||||
| 83 resources | 4.8 MiB | ||||||
CImage OptimizationAction22 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.
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.
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.
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.
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.
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.
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.
Image without explicit width/height — browser can't reserve space; CLS jumps when image loads.
Source: web.dev / Core Web Vitals
BHTTP/3 (QUIC)HTTP/3 not advertisedREVIEW
CCompression AlgorithmActionMain response served uncompressedREVIEW
BServer-Timing ObservabilityNo Server-Timing header foundREVIEW
BJavaScript Blocking2 JS blocking issue(s) detectedREVIEW
CGreen HostingActionWhether the site is served from green-energy infrastructureREVIEW
Green Hosting
No green hosting detected
BHTTP Cachingno-cacheREVIEW
no-cache
| Directive | Value | Meaning |
|---|---|---|
| no-cache | — | Cache but always revalidate first |
A+Text CompressionAll text resources are compressedPASS
A+Font Loading13 fonts (307 KB)PASS
Web fonts
13
307 KB total
Render-blocking
0
of 13
Dominant font-display
swap
Most common across fonts
Font loading timeline
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 CachingAll resources properly cachedPASS
A+Critical Rendering PathNo render-blocking resourcesPASS
A+Resource HintsNo optimization neededPASS
A+LCP Image PreloadLCP preload audit not availablePASS
A+Main HTML Cache-ControlMain HTML uses no-cache -- safe revalidate-on-request policyPASS
A+Server Response Intelligence1 server-response signal(s) detectedPASS
A+Render-Blocking ResourcesNo render-blocking resources detectedPASS
A+Third-Party ResourcesNo third-party resources detectedPASS
A+CSS Performance DepthNo CSS performance depth issues detectedPASS
Network Waterfall83 requests over 3715msINFO
Third-Party Script CostPer-script blocking time, transfer cost, and cache headersINFO
| Script | Category | Execution | Transfer | Unused | Monthly Cost | Verdict |
|---|---|---|---|---|---|---|
www.stib-mivb.be www.stib-mivb.be | Other | 1875ms | 0 KB | 49% | €10/mo | Costly |
www.stib-mivb.be www.stib-mivb.be | Other | 1228ms | 9 KB | — | €7/mo | Costly |
Unattributable Unattributable | Other | 1094ms | 0 KB | — | €6/mo | Costly |
tracking.stib-mivb.be tracking.stib-mivb.be | Other | 618ms | 534 KB | 36% | €3/mo | Costly |
www.stib-mivb.be www.stib-mivb.be | Other | 546ms | 0 KB | 70% | €3/mo | Costly |
Google Tag Manager www.googletagmanager.com | Tag Manager | 328ms | 145 KB | 36% | €2/mo | Costly |
Facebook Pixel connect.facebook.net | Advertising | 300ms | 125 KB | 28% | €2/mo | Costly |
consent.cookiebot.com consent.cookiebot.com | Other | 287ms | 36 KB | — | €2/mo | Costly |
Google Tag Manager www.googletagmanager.com | Tag Manager | 220ms | 130 KB | 46% | €1/mo | Costly |
tracking.stib-mivb.be tracking.stib-mivb.be | Other | 216ms | 381 KB | 51% | €1/mo | Costly |
Facebook Pixel connect.facebook.net | Advertising | 199ms | 97 KB | 36% | €1/mo | Optional |
consent.cookiebot.com consent.cookiebot.com | Other | 85ms | 0 KB | — | €0/mo | Optional |
www.stib-mivb.be www.stib-mivb.be | Other | 53ms | 95 KB | — | €0/mo | Optional |
These scripts may cost more than they're worth
- www.stib-mivb.be adds 1875ms and costs ~€10/month
- www.stib-mivb.be adds 1228ms and costs ~€7/month
- Unattributable adds 1094ms and costs ~€6/month
- tracking.stib-mivb.be adds 618ms and costs ~€3/month
- www.stib-mivb.be adds 546ms and costs ~€3/month
- Google Tag Manager adds 328ms and costs ~€2/month
- Facebook Pixel adds 300ms and costs ~€2/month
- consent.cookiebot.com adds 287ms and costs ~€2/month
- Google Tag Manager adds 220ms and costs ~€1/month
- tracking.stib-mivb.be adds 216ms and costs ~€1/month
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
www.stib-mivb.be takes 1875ms of CPU time. Consider loading it asynchronously or replacing it with a lighter alternative.
This script has high main-thread execution time — optimize hot paths or defer.
Source: web.dev
www.stib-mivb.be takes 1228ms of CPU time. Consider loading it asynchronously or replacing it with a lighter alternative.
This script has high main-thread execution time — optimize hot paths or defer.
Source: web.dev
Unattributable takes 1094ms of CPU time. Consider loading it asynchronously or replacing it with a lighter alternative.
This script has high main-thread execution time — optimize hot paths or defer.
Source: web.dev
tracking.stib-mivb.be takes 618ms of CPU time. Consider loading it asynchronously or replacing it with a lighter alternative.
This script has high main-thread execution time — optimize hot paths or defer.
Source: web.dev
www.stib-mivb.be takes 546ms of CPU time. Consider loading it asynchronously or replacing it with a lighter alternative.
This script has high main-thread execution time — optimize hot paths or defer.
Source: web.dev
70% of www.stib-mivb.be'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
Google Tag Manager takes 328ms of CPU time. Consider loading it asynchronously or replacing it with a lighter alternative.
This script has high main-thread execution time — optimize hot paths or defer.
Source: web.dev
Facebook Pixel takes 300ms of CPU time. Consider loading it asynchronously or replacing it with a lighter alternative.
This script has high main-thread execution time — optimize hot paths or defer.
Source: web.dev
consent.cookiebot.com takes 287ms of CPU time. Consider loading it asynchronously or replacing it with a lighter alternative.
This script has high main-thread execution time — optimize hot paths or defer.
Source: web.dev
Google Tag Manager takes 220ms of CPU time. Consider loading it asynchronously or replacing it with a lighter alternative.
This script has high main-thread execution time — optimize hot paths or defer.
Source: web.dev
tracking.stib-mivb.be takes 216ms of CPU time. Consider loading it asynchronously or replacing it with a lighter alternative.
This script has high main-thread execution time — optimize hot paths or defer.
Source: web.dev
51% of tracking.stib-mivb.be'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
Image Optimization14 images, 149 KB total, 72 KB wastedINFO
Image Optimization Audit
Total Images
14
Total Size
149 KB
Oversized
2
Wasted
72 KB