gc-estimate-emissions

name	gc-estimate-emissions
description	Estimate CO2 emissions for web pages using the Sustainable Web Design (SWD) v4 model. Works on a single page or an entire sitemap. Use when the user asks about page weight, page emissions, CO2 per visit, or digital carbon footprint.
license	MIT
metadata	{"author":"fullo","version":"1.1"}

Estimate Emissions

Estimate CO2 emissions per page view using the Sustainable Web Design Model v4 for $ARGUMENTS.

Heads-up — SCI for Web (2026). The GSF and W3C are developing SCI for Web (Q1 2026), an SCI profile that attributes web emissions across servers, networks, third parties, and end-user devices, with mandatory disclosure of boundaries and data sources. It complements SWD v4 rather than replacing it. Keep using SWD here, but always state your assumptions, data sources, and boundaries in the report so results map cleanly onto SCI for Web when it ratifies. See gsf-projects.md.

Steps

Single page

1. Determine page weight in bytes:

   • Use DevTools Network tab (disable cache, load page)
   • Or curl -sL [url] | wc -c for a rough estimate
   • Or use Lighthouse report transferred size

2. Estimate emissions:

   • Use the swd_estimate MCP tool with:
     • pageWeightBytes (required): total transfer size in bytes
     • monthlyVisitors: monthly unique visitors (enables monthly totals)
     • newVisitorRatio: fraction of new visitors, 0-1 (default: 0.75)
     • returnCacheRatio: cache hit ratio for returning visitors, 0-1 (default: 0.02)
     • carbonIntensity: grid intensity in gCO2eq/kWh (default: 494 global average)
   • To check green hosting: use check_green_hosting MCP tool with the domain
   • If MCP is not available, compute manually:
     • Energy per visit = bytes x 0.81 kWh/GB (adjusted for new/return visitor mix)
     • CO2 = energy x grid intensity (494 gCO2eq/kWh global average)
     • Green hosting reduces data center segment by ~81%

3. Report:

## Page Emissions: [url]

| Metric | Value |
|--------|-------|
| Page weight | ? KB |
| Green hosted | yes/no |
| CO2 per new visit | ? g |
| CO2 per return visit | ? g |
| CO2 per visit (blended) | ? g |
| Annual estimate (1000 visits/month) | ? kg CO2 |

### Breakdown by segment
| Segment | Share |
|---------|-------|
| Data centers | ?% |
| Networks | ?% |
| User devices | ?% |

### Methodology and sources
- Model: [Sustainable Web Design Model v4](https://sustainablewebdesign.org/estimating-digital-emissions/)
- Grid carbon intensity: [value] gCO2eq/kWh — [Ember Global Electricity Review](https://ember-energy.org/) [year], or tool default (494 global avg)
- New visitor ratio: [value] — [estimated / analytics data]
- Page weight source: [DevTools / curl / Lighthouse]
- Green hosting: [checked via Green Web Foundation API / not checked]

Multiple pages (sitemap)

1. Collect page weights for the most important pages (home, top landing pages, key flows)

2. Batch estimate:

   • Use the swd_batch MCP tool with:
     • pages (required): array of { "url": "...", "weightBytes": 123456 } objects
     • monthlyVisitors: monthly visitors for total calculation
     • carbonIntensity: grid intensity in gCO2eq/kWh (default: 494)
   • If MCP is not available: compute each page individually using the formula above

3. Report:

## Sitemap Emissions

| Page | Weight | CO2/visit | Annual (1k/mo) |
|------|--------|-----------|-----------------|
| / | ? KB | ? g | ? kg |
| /about | ? KB | ? g | ? kg |
| ... | ... | ... | ... |
| **Total** | **? KB** | **? g** | **? kg** |

### Heaviest pages
1. [url] — ? KB — [why it's heavy]
2. ...

### Recommendations
1. [action to reduce heaviest pages]
2. ...

### Methodology and sources
- Model: Sustainable Web Design Model v4 — sustainablewebdesign.org
- Grid carbon intensity: [value] gCO2eq/kWh — Ember [year]
- Page weights: [source]

Gotchas

• SWD model v4 estimates are order-of-magnitude: The Sustainable Web Design model provides rough estimates (plus or minus 50%). Do not present results with false precision (e.g., "1.234g CO2" — say "~1.2g CO2" instead).
• First visit vs return visit matters enormously: Cached resources can reduce transfer by 80%+. Always specify whether the estimate is for a first or return visit.
• Mobile vs desktop can differ by 2-3x: Mobile devices use less energy per page load but may transfer more data due to responsive images. Specify the device context.

Post-report verification

After presenting the emissions report, automatically run /gc-verify in quick mode. This triggers a Chain-of-Verification (CoVe) process: extract claims from the report, generate adversarial questions, answer each independently, and present findings under a ## Verification (CoVe) heading.

Context

• SWD estimates page-level emissions based on data transfer
• For operation-level carbon measurement (API calls, background jobs), use /gc-measure-sci
• For a full sustainability audit, use /gc-setup
• SWD and SCI are complementary: SWD measures the "weight" of what users see, SCI measures the "cost" of what the server does