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https://www.flixbus.com

Performance

· 14 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
75
GRADE
C
FIX
3
REVIEW
3
PASS
6
INFO
2

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

Mobile Desktop
80
Performance Overall performance score (0–100) based on Core Web Vitals and other metrics. 90+ is good.
89
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.
85
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.

792 ms

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

1.14 s

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

209 ms

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

0.165

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

1.93 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.

3.62 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 s
Checks
14
6 PASS 3 REVIEW 3 FIX
D
Page Weight Budget
Action
2.5 MB transferred, 182 requests
FIX
2.5 MB transferred, 182 requests
Warning::
Page weighs 6.4 MB (2.5 MB transferred)
Warning::
JavaScript is 1.7 MB — consider code splitting or lazy loading
Large JavaScript bundles delay interactivity. Split code by route or defer non-critical scripts.
Got: 1.7 MB
Warning::
182 HTTP requests — consider bundling or reducing
Each request adds latency. Bundle small files, use sprites, or eliminate unnecessary requests.
Info::
Estimated 0.53 g CO2 per page load
2.5 MB / 2.4 MB budget
2.5 MB transferred
182 requests
0.53 g CO2 per page load
JavaScript 1.7 MiB 67%
Images 689.2 KiB 27%
Fonts 62.7 KiB 2%
Other 51.2 KiB 2%
CSS 31.2 KiB 1%
HTML 22.2 KiB 1%
Other 2.7 KiB 0%
Other 0 B 0%
0 2.4 MB 4.9 MB
Over budget

Large JavaScript bundles delay interactivity. Split code by route or defer non-critical scripts.

Why this matters

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.

Why this matters

High HTTP request count — bundling, sprite-ing, and HTTP/2 server push can reduce per-request overhead.

Source: web.dev

D
Third-Party Impact
Action
99% third-party, 0 ms blocking
FIX
99% third-party, 0 ms blocking
Warning::
Third-party code accounts for 99% of page weight (2.5 MiB of 2.5 MiB)
Info::
Third-party blocking time is low (0 ms)
99%
First-party Third-party
F
JS Bundles
Action
45 scripts, 718 KB unused
FIX
45 scripts, 718 KB unused
Warning::
https://www.googletagmanager.com/gtm.js?id=GTM-QFH...: 73 KB unused (40%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.googletagmanager.com/gtag/js?id=AW-993...: 66 KB unused (45%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.googletagmanager.com/gtag/js?id=DC-133...: 63 KB unused (49%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.googletagmanager.com/gtag/js?id=DC-131...: 63 KB unused (49%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.googletagmanager.com/gtag/js?id=DC-133...: 63 KB unused (49%)
Consider code splitting or tree shaking to reduce unused code.
Info::
Total unused JavaScript: 718 KB
718 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://www.googletagmanager.com/gtm.js?id=GTM-QFH9M184 KB73 KB (40%)✓3rd
https://www.googletagmanager.com/gtag/js?id=AW-993552604&cx=c&gtm=4e6460146 KB66 KB (45%)✓3rd
https://www.googletagmanager.com/gtag/js?id=DC-13389221&cx=c&gtm=4e6460130 KB63 KB (49%)✓3rd
https://www.googletagmanager.com/gtag/js?id=DC-13118234&cx=c&gtm=4e6460130 KB63 KB (49%)✓3rd
https://www.googletagmanager.com/gtag/js?id=DC-13397442&cx=c&gtm=4e6460130 KB63 KB (49%)✓3rd
https://www.googletagmanager.com/gtag/js?id=DC-13513570&cx=c&gtm=4e6460130 KB63 KB (49%)✓3rd
https://www.googletagmanager.com/gtag/js?id=DC-14468760&cx=c&gtm=4e6460130 KB63 KB (49%)✓3rd
https://www.googletagmanager.com/gtag/js?id=DC-13147834&cx=c&gtm=4e6460130 KB63 KB (48%)✓3rd
https://d3k6pebee3cv6.cloudfront.net/search-mask/current/main.920e98fd.js220 KB61 KB (28%)✓3rd
https://app.usercentrics.eu/browser-ui/3.96.0/index.module.js120 KB53 KB (45%)✓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

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
Image Optimization
Action
66 images, 0 KB saveable
REVIEW
66 images, 0 KB saveable
Warning::
https://cdn-cf.cms.flixbus.com/drupal-assets/socia... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://cdn-cf.cms.flixbus.com/drupal-assets/socia... 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://cdn-cf.cms.flixbus.com/drupal-assets/logos... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://cdn-cf.cms.flixbus.com/drupal-assets/card-... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://cdn-cf.cms.flixbus.com/drupal-assets/socia... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://cdn-cf.cms.flixbus.com/drupal-assets/socia... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
66 images 689 KB
0 oversized -0 KB
57 legacy format
7 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

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

C
JS Execution Cost
Action
1939ms total JS execution
REVIEW
1939ms total JS execution
Warning::
Unattributable: 543ms CPU time
Warning::
https://www.googletagmanager.com/gtm.js?id=GTM-QFH...: 368ms CPU time
Warning::
https://www.flixbus.com/: 278ms CPU time
Info::
https://d3k6pebee3cv6.cloudfront.net/search-mask/c...: 246ms CPU time
Info::
https://app.usercentrics.eu/browser-ui/3.96.0/inde...: 111ms CPU time
Warning::
Third-party scripts: 1661ms (86% of total)

Main Thread Breakdown

Script Evaluation 57% Other 24% Style & Layout 7% Script Parsing & Compilation 6%
ScriptTotalScriptingParse/CompileParty
Unattributable543ms83ms0ms3rd
https://www.googletagmanager.com/gtm.js?id=GTM-QFH9M368ms321ms27ms3rd
https://www.flixbus.com/278ms30ms4ms1st
https://d3k6pebee3cv6.cloudfront.net/search-mask/current/main.920e98fd.js246ms193ms23ms3rd
https://app.usercentrics.eu/browser-ui/3.96.0/index.module.js111ms91ms0ms3rd
https://www.googletagmanager.com/gtag/js?id=DC-13513570&cx=c&gtm=4e6460109ms100ms8ms3rd
https://www.datadoghq-browser-agent.com/eu1/v5/datadog-rum.js105ms88ms10ms3rd
https://www.googletagmanager.com/gtag/js?id=DC-14468760&cx=c&gtm=4e646070ms54ms15ms3rd
https://account-widget.booking.flixbus.com/current/assets/main.CgKgh9lJ.js56ms43ms0ms3rd
https://www.googletagmanager.com/gtag/js?id=AW-993552604&cx=c&gtm=4e646052ms41ms10ms3rd
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
3 fonts (63 KB)
PASS
3 fonts (63 KB)
Info::
3 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

3

63 KB total

Render-blocking

0

of 3

Dominant font-display

swap

Most common across fonts

Font loading timeline
Transfer FOIT (block) FOUT (swap)
0 ms 500 ms 1.0 s FCP 792 ms LCP 1.1 shttps://honeycomb.flixbus.com/dist/15.3.3/font/roboto-latin-500-normal.woff2roboto-latin-500-normal... https://honeycomb.flixbus.com/dist/15.3.3/font/roboto-latin-500-normal.woff2 — 21.0 KiB — 0 ms — font-display: swaphttps://honeycomb.flixbus.com/dist/15.3.3/font/roboto-latin-700-normal.woff2roboto-latin-700-normal... https://honeycomb.flixbus.com/dist/15.3.3/font/roboto-latin-700-normal.woff2 — 21.0 KiB — 0 ms — font-display: swaphttps://honeycomb.flixbus.com/dist/15.3.3/font/roboto-latin-400-normal.woff2roboto-latin-400-normal... https://honeycomb.flixbus.com/dist/15.3.3/font/roboto-latin-400-normal.woff2 — 20.7 KiB — 0 ms — font-display: swap
roboto-latin-500-normal... woff2 swap
Size 21 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
roboto-latin-700-normal... woff2 swap
Size 21 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
roboto-latin-400-normal... woff2 swap
Size 21 KB
Load time 0 ms
Start 0 ms
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
A+
HTTP Caching
max-age=300 (5 minutes)
PASS
max-age=300 (5 minutes)
Info::
Cache-Control header is set
Got: public, max-age=300, max-stale=86400, stale-if-error=86400, stale-while-revalidate=86400
Info::
Effective TTL: 5 minutes (max-age=300)
Info::
Last-Modified header present
Cache-Control

public, max-age=300, max-stale=86400, stale-if-error=86400, stale-while-revalidate=86400

DirectiveValueMeaning
public—Any cache may store this response
max-age300Cache for 5 minutes
max-stale86400
stale-if-error86400
stale-while-revalidate86400Serve stale for 1 day while fetching fresh
Effective TTL: 300 seconds
Network Waterfall
182 requests over 0ms
INFO

Performance analysis not available for this result.

Third-Party Script Cost
Per-script blocking time, transfer cost, and cache headers
INFO
86% of JavaScript execution is third-party
First-party Third-party 1661ms · 1036KB · $22/mo
Unattributable
Other
Costly
Execution 543ms
Transfer 0 KB
Monthly Cost $7/mo
Google Tag Manager
Tag Manager
Costly
Execution 368ms
Transfer 184 KB
Unused 40%
Monthly Cost $5/mo
d3k6pebee3cv6.cloudfront.net
Other
Costly
Execution 246ms
Transfer 220 KB
Unused 28%
Monthly Cost $3/mo
app.usercentrics.eu
Other
Optional
Execution 111ms
Transfer 120 KB
Unused 45%
Monthly Cost $1/mo
Google Tag Manager
Tag Manager
Optional
Execution 109ms
Transfer 130 KB
Unused 49%
Monthly Cost $1/mo
www.datadoghq-browser-agent.com
Other
Optional
Execution 105ms
Transfer 52 KB
Unused 56%
Monthly Cost $1/mo
Google Tag Manager
Tag Manager
Optional
Execution 70ms
Transfer 130 KB
Unused 49%
Monthly Cost $1/mo
account-widget.booking.flixbus.com
Other
Optional
Execution 56ms
Transfer 55 KB
Unused 58%
Monthly Cost $1/mo
Google Tag Manager
Tag Manager
Optional
Execution 52ms
Transfer 146 KB
Unused 45%
Monthly Cost $1/mo

These scripts may cost more than they're worth

  • Unattributable adds 543ms and costs ~$7/month
  • Google Tag Manager adds 368ms and costs ~$5/month
  • d3k6pebee3cv6.cloudfront.net adds 246ms and costs ~$3/month

86% 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

Unattributable takes 543ms 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

Google Tag Manager takes 368ms 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

d3k6pebee3cv6.cloudfront.net takes 246ms 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

56% of www.datadoghq-browser-agent.com'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

58% of account-widget.booking.flixbus.com'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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