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https://www.flixbus.com

Performance

· 16 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
75
GRADE
C
FIX
4
REVIEW
2
PASS
8
INFO
2

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

Mobile Desktop
22
Performance Overall performance score (0–100) based on Core Web Vitals and other metrics. 90+ is good.
93
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.

3.41 s

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

12.29 s

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

1.54 s

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

0.291

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

6.41 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.

15.52 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
16
8 PASS 2 REVIEW 4 FIX
D
Page Weight Budget
Action
2.2 MB transferred, 183 requests
FIX
2.2 MB transferred, 183 requests
Info::
Page weighs 6.1 MB (2.2 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::
183 HTTP requests — consider bundling or reducing
Each request adds latency. Bundle small files, use sprites, or eliminate unnecessary requests.
Info::
Estimated 0.46 g CO2 per page load
2.2 MB / 2.4 MB budget
2.2 MB transferred
183 requests
0.46 g CO2 per page load
JavaScript 1.7 MiB 78%
Images 328.3 KiB 15%
Fonts 62.6 KiB 3%
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
Approaching limit

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 (2.2 MiB of 2.2 MiB)
Info::
Third-party blocking time is low (0 ms)
99%
First-party Third-party
F
JS Execution Cost
Action
7085ms total JS execution
FIX
7085ms total JS execution
Warning::
Unattributable: 1775ms CPU time
Warning::
https://www.googletagmanager.com/gtm.js?id=GTM-QFH...: 951ms CPU time
Warning::
https://d3k6pebee3cv6.cloudfront.net/search-mask/c...: 913ms CPU time
Warning::
https://app.usercentrics.eu/browser-ui/3.96.0/inde...: 615ms CPU time
Warning::
https://www.flixbus.com/: 597ms CPU time
Warning::
Third-party scripts: 6488ms (92% of total)

Main Thread Breakdown

Script Evaluation 55% Other 26% Style & Layout 8% Script Parsing & Compilation 8%
ScriptTotalScriptingParse/CompileParty
Unattributable1775ms257ms0ms3rd
https://www.googletagmanager.com/gtm.js?id=GTM-QFH9M951ms819ms70ms3rd
https://d3k6pebee3cv6.cloudfront.net/search-mask/current/main.920e98fd.js913ms619ms171ms3rd
https://app.usercentrics.eu/browser-ui/3.96.0/index.module.js615ms410ms3ms3rd
https://www.flixbus.com/597ms67ms9ms1st
https://www.googletagmanager.com/gtag/js?id=DC-13118234&cx=c&gtm=4e6460380ms343ms34ms3rd
https://www.datadoghq-browser-agent.com/eu1/v5/datadog-rum.js307ms250ms17ms3rd
https://www.googletagmanager.com/gtag/js?id=DC-13147834&cx=c&gtm=4e6460216ms169ms45ms3rd
https://www.googletagmanager.com/gtag/js?id=AW-993552604&cx=c&gtm=4e6460191ms151ms36ms3rd
https://cdn-cf.cms.flixbus.com/drupal-assets/flix-home-assets/main.52f17b.js177ms88ms7ms3rd

Showing top 10 of 18 scripts

F
JS Bundles
Action
45 scripts, 735 KB unused
FIX
45 scripts, 735 KB unused
Warning::
https://d3k6pebee3cv6.cloudfront.net/search-mask/c...: 78 KB unused (36%)
Consider code splitting or tree shaking to reduce unused code.
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-133...: 63 KB unused (49%)
Consider code splitting or tree shaking to reduce unused code.
Info::
Total unused JavaScript: 735 KB
735 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://d3k6pebee3cv6.cloudfront.net/search-mask/current/main.920e98fd.js220 KB78 KB (36%)✓3rd
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-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-13118234&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://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/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/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::
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/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.
66 images 328 KB
0 oversized -0 KB
58 legacy format
6 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

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
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 2.0 s 4.0 s 6.0 s 8.0 s 10.0 s 12.0 s FCP 3.4 s LCP 12.3 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
5 hints, 0 missing preconnects
PASS
5 hints, 0 missing preconnects
Info::
Page uses 5 resource hint(s)

Current Resource Hints

preconnect
3
preload
2
dns-prefetch
—
prefetch
—

5 resource hints configured

A+
Render-Blocking Resources
No render-blocking resources detected
PASS
No render-blocking resources detected
Info::
No render-blocking resources detected in <head>
A+
Third-Party Resources
No third-party resources detected
PASS
No third-party resources detected
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
183 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
92% of JavaScript execution is third-party
First-party Third-party 6488ms · 1614KB · $86/mo
Unattributable
Other
Costly
Execution 1775ms
Transfer 0 KB
Monthly Cost $24/mo
Google Tag Manager
Tag Manager
Costly
Execution 951ms
Transfer 184 KB
Unused 40%
Monthly Cost $13/mo
d3k6pebee3cv6.cloudfront.net
Other
Costly
Execution 913ms
Transfer 220 KB
Unused 36%
Monthly Cost $12/mo
app.usercentrics.eu
Other
Costly
Execution 615ms
Transfer 120 KB
Unused 45%
Monthly Cost $8/mo
Google Tag Manager
Tag Manager
Costly
Execution 380ms
Transfer 130 KB
Unused 49%
Monthly Cost $5/mo
www.datadoghq-browser-agent.com
Other
Costly
Execution 307ms
Transfer 52 KB
Unused 56%
Monthly Cost $4/mo
Google Tag Manager
Tag Manager
Costly
Execution 216ms
Transfer 130 KB
Unused 48%
Monthly Cost $3/mo
Google Tag Manager
Tag Manager
Optional
Execution 191ms
Transfer 146 KB
Unused 45%
Monthly Cost $3/mo
cdn-cf.cms.flixbus.com
Other
Optional
Execution 177ms
Transfer 18 KB
Monthly Cost $2/mo
Google Tag Manager
Tag Manager
Optional
Execution 150ms
Transfer 130 KB
Unused 49%
Monthly Cost $2/mo
Google Tag Manager
Tag Manager
Optional
Execution 138ms
Transfer 130 KB
Unused 49%
Monthly Cost $2/mo
Google Tag Manager
Tag Manager
Optional
Execution 131ms
Transfer 130 KB
Unused 49%
Monthly Cost $2/mo
Google Tag Manager
Tag Manager
Optional
Execution 131ms
Transfer 130 KB
Unused 49%
Monthly Cost $2/mo
account-widget.booking.flixbus.com
Other
Optional
Execution 130ms
Transfer 55 KB
Unused 58%
Monthly Cost $2/mo
honeycomb-icons.hive.flixbus.com
Other
Optional
Execution 120ms
Transfer 5 KB
Monthly Cost $2/mo
d2kfg2dwwf7b20.cloudfront.net
Other
Optional
Execution 113ms
Transfer 25 KB
Monthly Cost $2/mo
app.usercentrics.eu
Other
Optional
Execution 50ms
Transfer 11 KB
Monthly Cost $1/mo

These scripts may cost more than they're worth

  • Unattributable adds 1775ms and costs ~$24/month
  • Google Tag Manager adds 951ms and costs ~$13/month
  • d3k6pebee3cv6.cloudfront.net adds 913ms and costs ~$12/month
  • app.usercentrics.eu adds 615ms and costs ~$8/month
  • Google Tag Manager adds 380ms and costs ~$5/month
  • www.datadoghq-browser-agent.com adds 307ms and costs ~$4/month
  • Google Tag Manager adds 216ms and costs ~$3/month

92% 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 1775ms 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 951ms 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 913ms 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

app.usercentrics.eu takes 615ms 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 380ms 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

www.datadoghq-browser-agent.com takes 307ms 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

Google Tag Manager takes 216ms 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

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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