https://www.gov.uk
Sustainability
· 8 checks — CO2 emissions, green hosting, repeat-visit weight, carbon budget, and transfer efficiency rolled into one auditable list.SCORE
92
GRADE
A
FIX
0
REVIEW
3
PASS
4
INFO
1
Checks
84 PASS 3 REVIEW
BTransfer Efficiency86% efficientREVIEW
Transfer Efficiency
86% efficient
86% efficient
Info::
Transfer efficiency: 86%
An estimated 26 KB (14%) could be eliminated: 0 KB via better compression, 0 KB via modern image formats, 26 KB of unused JavaScript. This wasted data produces 0.01g of unnecessary CO2 per page view.
Total waste: 26 KB (14% of page weight)
Unused JS 26 KB
0.01g unnecessary CO2 per visit
Actual transfer 189 KB
Theoretical minimum 163 KB
Potential savings 26 KB (0.01g CO2)
See Deep Analysis sections above for specific optimizations.
BWeb Font Weight VariantsNo detectable Google Fonts weightsREVIEW
Web Font Weight Variants
No detectable Google Fonts weights
No detectable Google Fonts weights
Info::
No detectable Google Fonts weights
The analyzer detects font weights via Google Fonts URL parameters (~70% of font-using sites). Self-hosted fonts and non-Google CDN fonts aren't visible to URL-based detection. If you self-host fonts, manually audit how many @font-face weights you ship -- 2-3 weights per family is typically enough; 5+ is usually unused payload.
CGreen HostingActionWhether the site is served from green-energy infrastructureREVIEW
Green Hosting
ActionWhether the site is served from green-energy infrastructure
Green Hosting
No green hosting detected
A+CO2 Per Page Load0.04g CO2 per viewPASS
CO2 Per Page Load
0.04g CO2 per view
0.04g CO2 per view
Info::
0.04g CO2 per page view
This page transfers 0.2 MB, producing an estimated 0.04g of CO2 per visit using the Sustainable Web Design model (v4). Breakdown: data center 0.00g, network 0.01g, end-user device 0.03g.
Got: 0.04g CO2 Expected: < 0.50g (sustainability target)
Info::
At 10,000 monthly views: 5.3 kg CO2/year
With 10,000 page views per month, this page would generate approximately 5.3 kg of CO2 annually — equivalent to charging 658 smartphones.
Info::
Green hosting reduces data center emissions
0.04g
Carbon Footprint per page view
✓ Below sustainability target (0.50g)
Cleaner than 90% of websites
Sustainable Web Design model v4 · Page size: 0.2 MB
Your site
0.04g
Top 10%
0.20g
Target
0.50g
Median website
0.60g
Energy Breakdown
Data center
0.00g
Network
0.01g
End-user device
0.03g
At 10,000 monthly views: Monthly: 0.4 kg · Annual: 5.3 kg · ≈ 658 smartphone charges
AGreen HostingGreen (cdn)PASS
Green Hosting
Green (cdn)
Green (cdn)
Info::
Fastly CDN uses renewable energy
Since most traffic is served through the CDN, the majority of data transfer energy is renewable.
Info::
Fastly: 100% renewable energy for edge network
Info::
Green hosting status based on known provider commitments
Green hosting detection uses a curated database of provider renewable energy commitments. This is not a real-time verification. For authoritative checks, visit thegreenwebfoundation.org.
Green Hosting✓ Green Hosted
Hosting Not identified✗CDN Fastly✓
Fastly: 100% renewable energy for edge network
Based on known provider commitments. Verify at thegreenwebfoundation.org
A+Repeat Visit Weight93% cachedPASS
Repeat Visit Weight
93% cached
93% cached
Info::
93% reduction on repeat visits
Returning visitors download only 13 KB (vs 189 KB first visit). 14 of 15 resources are served from browser cache, saving 0.04g CO2 per repeat visit.
Info::
Repeat visit: 0.00g CO2 (first visit: 0.04g)
First visit
189 KB
Repeat visit
13 KB
93% reduction on repeat visits
Saving 0.04g CO2 per returning visitor
14 resources served from cache · 1 resources re-downloaded
A+Carbon Budget10th percentilePASS
Carbon Budget
10th percentile
10th percentile
Info::
0.04g CO2 — below the sustainability target of 0.50g
Cleaner than an estimated 90% of websites analyzed. This page meets the Web Sustainability Guidelines target.
Info::
Estimated 10th percentile
Compared to: top 10% = 0.20g, target = 0.50g, median = 0.60g per page view.
Top 10%
Target
Median website
0.04g
10th percentile
Cleaner than 90% of websites
✓ Below the Web Sustainability Guidelines target
vs Median 93% cleaner ✓
vs Target 91% cleaner ✓
Image Optimization4 images, 3 KB total, 2 KB wastedINFO
Image Optimization
4 images, 3 KB total, 2 KB wasted
Image Optimization Audit
Total Images
4
Total Size
3 KB
Oversized
2
Wasted
2 KB
4 missing alt text
All checks on this page are automated. Results are estimates - run targeted manual reviews when the score affects a release decision.