Carbon-Aware Code Auditor
Measure the carbon cost
of your code
Analyse the real energy footprint of any web page, get actionable optimisation suggestions, and schedule backend tasks when the grid is greenest. Unlike estimate-based tools, Jarrly fetches your page and every linked resource to measure actual file sizes — no guesswork.
Energy-Impact Report
Enter a URL to analyse the real energy cost of loading that page per 1,000 visitors, or enter page metrics manually.
Energy Impact Report
Resource Breakdown
Optimisation Suggestions
Run an audit first, then see specific recommendations to reduce your page's energy footprint. Or browse general best practices below.
Based on Your Audit
General Best Practices
Use modern image formats
Switch from JPEG/PNG to WebP or AVIF. Typical savings: 25–50% file size with no visible quality loss.
High impactReduce JavaScript bundles
Tree-shake unused code, code-split by route, and defer non-critical scripts. Every 100KB of JS costs ~0.5s of CPU time on mobile.
High impactImplement effective caching
Set long Cache-Control headers for static assets and use content hashing in filenames. Returning visitors skip re-downloading unchanged files.
High impactMinimise API polling
Replace polling with WebSockets or Server-Sent Events. A page polling every 5 seconds generates 720 requests/hour — most returning unchanged data.
Medium impactSelf-host fonts & subset
Host fonts locally instead of loading from Google Fonts (saves a DNS lookup + connection). Subset to only the characters you need.
Medium impactLazy-load below-the-fold content
Use loading="lazy" on images and iframes. Only load what the user can see — defer the rest until they scroll.
Choose a green host
Host with a provider that runs on renewable energy. Check The Green Web Foundation directory.
FoundationalUse a CDN
Serve static assets from edge nodes close to users. Shorter network paths = less energy in transit. Most CDNs also handle compression.
FoundationalCarbon-Aware Scheduling
Schedule heavy backend tasks (builds, batch jobs, backups) when the UK power grid is using the most renewable energy. Live data from the National Grid ESO.
Current Grid Carbon Intensity
Live48-Hour Forecast
Green periods are the best times to run energy-intensive tasks.
Best Time to Run Jobs
Loading forecast data...
Scheduling Tips
- Run CI/CD pipelines, data processing, and backups during low-carbon windows
- Overnight (1am–5am) often has lower intensity due to wind generation
- Midday on sunny days can also be low-carbon thanks to solar
- Avoid peak hours (5pm–7pm) when gas plants ramp up to meet demand
- Use cron scheduling or cloud schedulers to automate green timing