https://www.readingrockets.org
Sustainability
· 8 checks — CO2 emissions, green hosting, repeat-visit weight, carbon budget, and transfer efficiency rolled into one auditable list.SCORE
87
GRADE
B
FIX
0
REVIEW
3
PASS
4
INFO
1
Checks
84 PASS 3 REVIEW
BTransfer Efficiency89% efficientREVIEW
Transfer Efficiency
89% efficient
89% efficient
Info::
Transfer efficiency: 89%
An estimated 177 KB (11%) could be eliminated: 0 KB via better compression, 0 KB via modern image formats, 177 KB of unused JavaScript. This wasted data produces 0.04g of unnecessary CO2 per page view.
Total waste: 177 KB (11% of page weight)
Unused JS 177 KB
0.04g unnecessary CO2 per visit
Actual transfer 1560 KB
Theoretical minimum 1382 KB
Potential savings 177 KB (0.04g 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
ACO2 Per Page Load0.36g CO2 per viewPASS
CO2 Per Page Load
0.36g CO2 per view
0.36g CO2 per view
Info::
0.36g CO2 per page view
This page transfers 1.5 MB, producing an estimated 0.36g of CO2 per visit using the Sustainable Web Design model (v4). Breakdown: data center 0.01g, network 0.07g, end-user device 0.28g.
Got: 0.36g CO2 Expected: < 0.50g (sustainability target)
Info::
At 10,000 monthly views: 43.3 kg CO2/year
With 10,000 page views per month, this page would generate approximately 43.3 kg of CO2 annually — equivalent to charging 5410 smartphones.
Info::
Green hosting reduces data center emissions
0.36g
Carbon Footprint per page view
✓ Below sustainability target (0.50g)
Cleaner than 74% of websites
Sustainable Web Design model v4 · Page size: 1.5 MB
Your site
0.36g
Top 10%
0.20g
Target
0.50g
Median website
0.60g
Energy Breakdown
Data center
0.01g
Network
0.07g
End-user device
0.28g
At 10,000 monthly views: Monthly: 3.6 kg · Annual: 43.3 kg · ≈ 5410 smartphone charges
AGreen HostingGreen (cdn)PASS
Green Hosting
Green (cdn)
Green (cdn)
Info::
Cloudflare CDN uses renewable energy
Since most traffic is served through the CDN, the majority of data transfer energy is renewable.
Info::
Cloudflare: 100% renewable energy for global network since 2019
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 Platform.sh✗CDN Cloudflare✓
Cloudflare: 100% renewable energy for global network since 2019
Based on known provider commitments. Verify at thegreenwebfoundation.org
A+Repeat Visit Weight97% cachedPASS
Repeat Visit Weight
97% cached
97% cached
Info::
97% reduction on repeat visits
Returning visitors download only 50 KB (vs 1560 KB first visit). 62 of 63 resources are served from browser cache, saving 0.35g CO2 per repeat visit.
Info::
Repeat visit: 0.01g CO2 (first visit: 0.36g)
First visit
1560 KB
Repeat visit
50 KB
97% reduction on repeat visits
Saving 0.35g CO2 per returning visitor
62 resources served from cache · 1 resources re-downloaded
ACarbon Budget26th percentilePASS
Carbon Budget
26th percentile
26th percentile
Info::
0.36g CO2 — below the sustainability target of 0.50g
Cleaner than an estimated 74% of websites analyzed. This page meets the Web Sustainability Guidelines target.
Info::
Estimated 26th percentile
Compared to: top 10% = 0.20g, target = 0.50g, median = 0.60g per page view.
Top 10%
Target
Median website
0.36g
26th percentile
Cleaner than 74% of websites
✓ Below the Web Sustainability Guidelines target
vs Median 40% cleaner ✓
vs Target 28% cleaner ✓
Image Optimization44 images, 1039 KB total, 55 KB wastedINFO
Image Optimization
44 images, 1039 KB total, 55 KB wasted
Image Optimization Audit
Total Images
44
Total Size
1039 KB
Oversized
3
Wasted
55 KB
2 missing dimensions 1 missing lazy loading
All checks on this page are automated. Results are estimates - run targeted manual reviews when the score affects a release decision.