Browsers will use heuristic caching, which can be unpredictable. Set explicit cache headers.
No Cache-Control header
Adding a Cache-Control header can significantly improve repeat-visit performance.
C
Image Optimization
Action
37 images, 0 KB saveable
REVIEW
37 images, 0 KB saveable
Warning::
!
https://www.cambridgeenglish.org/Images/trust_engl... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
!
https://www.cambridgeenglish.org/Images/cambridge-... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
!
https://www.cambridgeenglish.org/Images/Kings-Coll... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
!
https://www.cambridgeenglish.org/Images/courses-an... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
!
https://www.cambridgeenglish.org/Images/cambridge-... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
!
https://www.cambridgeenglish.org/Images/McGill-log... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
!
https://www.cambridgeenglish.org/Images/english-pr... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
!
https://www.cambridgeenglish.org/Images/world-shap... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
!
https://www.cambridgeenglish.org/Images/girl-takin... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
!
https://www.cambridgeenglish.org/Images/Monash-Uni... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
!
https://www.cambridgeenglish.org/Images/Accenture-... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
!
https://www.cambridgeenglish.org/Images/Cambridge_... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
!
https://www.cambridgeenglish.org/Images/bsi-logo-f... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
!
https://www.cambridgeenglish.org/Images/digital-to... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
!
https://www.cambridgeenglish.org/Images/P-and-G-lo... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
!
https://www.cambridgeenglish.org/Images/promise-to... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
!
https://www.cambridgeenglish.org/Images/alte-logo-... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
37images1.9 MB
0oversized-0 KB
36legacy format
17missing dimensionsCLS 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
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
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
9 fonts (267 KB)
PASS
9 fonts (267 KB)
Info::
i
9 font(s) use font-display: swap (FOUT risk but functional)
Web fonts
9
267 KB total
Render-blocking
0
of 9
Dominant font-display
swap
Most common across fonts
Font loading timeline
TransferFOIT (block)FOUT (swap)
6xK3dSBYKcSV-LCoeQqfX1R...woff2swap
Size15 KB
Load time35 ms
Start590 ms
RiskFOUT — text flashes from fallback to web font
6xKydSBYKcSV-LCoeQqfX1R...woff2swap
Size15 KB
Load time39 ms
Start591 ms
RiskFOUT — text flashes from fallback to web font
6xKydSBYKcSV-LCoeQqfX1R...woff2swap
Size14 KB
Load time46 ms
Start591 ms
RiskFOUT — text flashes from fallback to web font
KFO7CnqEu92Fr1ME7kSn66a...woff2swap
Size34 KB
Load time99 ms
Start611 ms
RiskFOUT — text flashes from fallback to web font
fontawesome-webfont.woffwoffswap
Size64 KB
Load time163 ms
Start698 ms
RiskFOUT — text flashes from fallback to web font
Convert to woff2 for ~30% smaller file size
KFO7CnqEu92Fr1ME7kSn66a...woff2swap
Size39 KB
Load time38 ms
Start864 ms
RiskFOUT — text flashes from fallback to web font
memtYaGs126MiZpBA-UFUIc...woff2swap
Size44 KB
Load time38 ms
Start1.1 s
RiskFOUT — text flashes from fallback to web font
memvYaGs126MiZpBA-UvWbX...woff2swap
Size42 KB
Load time37 ms
Start1.2 s
RiskFOUT — text flashes from fallback to web font
KFO7CnqEu92Fr1ME7kSn66a...woff2swap
Size0 KB
Load time1 ms
Start1.2 s
RiskFOUT — 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)
Fixing the unchecked items could save ~19 KB and ~38 ms
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+
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
Network Waterfall
134 requests over 4416ms
INFO
HTML JavaScript CSS Images Fonts XHR/Fetch Other
Third-Party Script Cost
Per-script blocking time, transfer cost, and cache headers
INFO
100%of JavaScript execution is third-party
First-party Third-party3373ms · 1056KB · £50/mo
Script
Category
Execution
Transfer
Unused
Monthly Cost
Verdict
Unattributable
Unattributable
Other
644ms
0 KB
—
£10/mo
Costly
Google Tag Manager
www.googletagmanager.com
Tag Manager
518ms
174 KB
44%
£8/mo
Costly
cdn-ukwest.onetrust.com
cdn-ukwest.onetrust.com
Other
464ms
120 KB
52%
£7/mo
Costly
Google Tag Manager
www.googletagmanager.com
Tag Manager
368ms
171 KB
37%
£5/mo
Costly
www.cambridgeenglish.org
www.cambridgeenglish.org
Other
331ms
12 KB
—
£5/mo
Costly
www.cambridgeenglish.org
www.cambridgeenglish.org
Other
261ms
63 KB
90%
£4/mo
Costly
www.gstatic.com
www.gstatic.com
Other
212ms
362 KB
67%
£3/mo
Costly
www.cambridgeenglish.org
www.cambridgeenglish.org
Other
199ms
33 KB
—
£3/mo
Optional
cse.google.com
cse.google.com
Other
141ms
4 KB
—
£2/mo
Optional
www.cambridgeenglish.org
www.cambridgeenglish.org
Other
99ms
7 KB
—
£1/mo
Optional
www.google.com
www.google.com
Other
69ms
103 KB
51%
£1/mo
Optional
cdn-ukwest.onetrust.com
cdn-ukwest.onetrust.com
Other
66ms
7 KB
—
£1/mo
Optional
Unattributable
Other
Costly
Execution644ms
Transfer0 KB
Monthly Cost£10/mo
Google Tag Manager
Tag Manager
Costly
Execution518ms
Transfer174 KB
Unused44%
Monthly Cost£8/mo
cdn-ukwest.onetrust.com
Other
Costly
Execution464ms
Transfer120 KB
Unused52%
Monthly Cost£7/mo
Google Tag Manager
Tag Manager
Costly
Execution368ms
Transfer171 KB
Unused37%
Monthly Cost£5/mo
www.cambridgeenglish.org
Other
Costly
Execution331ms
Transfer12 KB
Monthly Cost£5/mo
www.cambridgeenglish.org
Other
Costly
Execution261ms
Transfer63 KB
Unused90%
Monthly Cost£4/mo
www.gstatic.com
Other
Costly
Execution212ms
Transfer362 KB
Unused67%
Monthly Cost£3/mo
www.cambridgeenglish.org
Other
Optional
Execution199ms
Transfer33 KB
Monthly Cost£3/mo
cse.google.com
Other
Optional
Execution141ms
Transfer4 KB
Monthly Cost£2/mo
www.cambridgeenglish.org
Other
Optional
Execution99ms
Transfer7 KB
Monthly Cost£1/mo
www.google.com
Other
Optional
Execution69ms
Transfer103 KB
Unused51%
Monthly Cost£1/mo
cdn-ukwest.onetrust.com
Other
Optional
Execution66ms
Transfer7 KB
Monthly Cost£1/mo
These scripts may cost more than they're worth
Unattributable adds 644ms and costs ~£10/month
Google Tag Manager adds 518ms and costs ~£8/month
cdn-ukwest.onetrust.com adds 464ms and costs ~£7/month
Google Tag Manager adds 368ms and costs ~£5/month
www.cambridgeenglish.org adds 331ms and costs ~£5/month
www.cambridgeenglish.org adds 261ms and costs ~£4/month
www.gstatic.com adds 212ms and costs ~£3/month
100% 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 644ms 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 518ms 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
cdn-ukwest.onetrust.com takes 464ms 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
52% of cdn-ukwest.onetrust.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 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
www.cambridgeenglish.org takes 331ms 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.cambridgeenglish.org takes 261ms 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
90% of www.cambridgeenglish.org'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
www.gstatic.com takes 212ms 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
67% of www.gstatic.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
51% of www.google.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.