www.netlify.com/blog/one-prompt-11-models-very-different-results

The numbers

First visit

0.390 g CO₂e

Return visit

0.0099 g CO₂e

Hosting

unknown

LCP

296 ms

CLS

0.182

TTFB

15 ms

At 10,000 views a month this page emits about 35.4 kg CO₂e a year, roughly 145 km in an average petrol car. The estimate assumes 75% new and 25% returning visitors, a measured cache reload ratio of 3%, and world-average grid intensity. How we calculate this

1. Audit third-party servicessave ~0.115 g/visit (1.03 MB)High impact · moderate effort

   14 third-party domains account for 2.05 MB (78% of the page).

   Remove services that no longer earn their place; load the rest on interaction (facades for embeds, delayed consent-gated tags). Each third party is also a privacy and performance dependency.

   • www.gstatic.com1.42 MB
   • js.hsforms.net201 kB
   • cdn.cookielaw.org192 kB
   • cdn.sanity.io78 kB
   • www.google.com60 kB
   • js.hs-analytics.net44 kB

   WSG 3.5: Treat third parties the same as first parties
2. Reduce JavaScript payloadsave ~0.055 g/visit (488 kB)High impact · moderate effort

   34 scripts total 1.95 MB on the wire (5.13 MB decoded). Bundles this size usually carry a lot of unused code.

   Split bundles per route, tree-shake dependencies, and audit with a bundle analyzer or coverage profile. A 25% cut is a conservative target for bundles this size.

   • recaptcha__en.js344 kB
   • recaptcha__en.js344 kB
   • recaptcha__en.js344 kB
   • recaptcha__en.js344 kB
   • v2.js201 kB

   WSG 3.2: Minify and remove unused codeWSG 3.3: Modularize bandwidth-heavy components
3. Convert and compress imagessave ~0.0053 g/visit (47 kB)Medium impact · quick fix

   9 images (104 kB) ship in legacy formats (JPEG/PNG/GIF).

   Serve AVIF (or WebP) with responsive srcset sizes, and re-compress oversized files. AVIF typically halves JPEG weight at the same visual quality.

   • be563e8998105c7e95b4db9110fa16b47cb68acd-230x…78 kB
   • ot_company_logo.png20 kB
   • logo_48.png2.3 kB
   • counters.gif1.0 kB
   • counters.gif1.0 kB

   WSG 2.9: Optimize media to reduce resource use
4. Lazy-load below-the-fold mediasave ~0.0016 g/visit (14 kB)Medium impact · quick fix

   2 below-the-fold images/iframes (107 kB) download immediately for every visitor.

   Add loading="lazy" to below-fold img and iframe elements (and keep it off the LCP image). Browsers then fetch them only when scrolling approaches.

   • be563e8998105c7e95b4db9110fa16b47cb68acd-230x…78 kB
   • anchor29 kB

   WSG 2.9: Optimize media to reduce resource use
5. Verify your hosting energyMedium impact · moderate effort

   This host has not published renewable energy evidence with the Green Web Foundation, so its energy source is unknown.

   Choose a provider listed in the Green Web Directory, or ask your current provider to publish evidence (and a carbon.txt). This cuts the data-center share of every single page view.

   • carbon.txtNo carbon.txt found at the site root; publishing one is the lightest first step.

   WSG 4.1: Use sustainable hosting
6. Upgrade compression beyond gzipsave ~0.032 g/visit (286 kB)Advisory · quick fix

   1.91 MB of text ships gzip-compressed; Brotli or Zstandard would cut roughly another 15-20%, and browsers without them fall back to gzip automatically.

   Serve precompressed Brotli for static text assets (highest level, compressed at build time) and enable Brotli or zstd for dynamic responses; keep gzip only as the fallback.

   • recaptcha__en.js344 kB
   • recaptcha__en.js344 kB
   • recaptcha__en.js344 kB
   • recaptcha__en.js344 kB
   • v2.js201 kB

   WSG 4.3: Reduce data transfer with compression
7. Stop downloading the same asset twicesave ~0.012 g/visit (103 kB)Advisory · quick fix

   1 asset was fetched more than once in a single page load (1.03 MB of repeated transfer).

   Usually a script injected twice or cache-busting query strings that differ per reference. Load each asset once and let the HTTP cache do its job.

   • recaptcha__en.js4 downloads · 1.38 MB

   WSG 3.2: Minify and remove unused code
8. Optimize web fontssave ~0.011 g/visit (100 kB)Advisory · quick fix

   6 font files total 285 kB.

   Subset fonts to used glyphs, prefer one variable font over multiple weights, serve WOFF2 only, and consider system fonts for UI text.

   • InstrumentSans-Italic_wdth_wght_.pMV_u3Uy.woff295 kB
   • InstrumentSans_wdth_wght_.tWV223Ma.woff289 kB
   • KFO7CnqEu92Fr1ME7kSn66aGLdTylUAMa3yUBA.woff241 kB
   • MartianMono-Medium.BnDjRSrk.woff232 kB
   • Figtree_wght_.DbGe-NNA.woff228 kB

   WSG 2.11: Use optimized web typography
9. Set a page-weight budgetAdvisory · moderate effort

   At 2.63 MB per view this page rates E. The findings above list where the weight is.

   Agree a transfer budget (e.g. under 975 kB reaches a B), enforce it in CI, and re-scan after each change to hold the line.

   WSG 3.1: Set goals based on performance and energy impact
10. Simplify the document structureAdvisory · larger effort

    The page renders 1599 DOM elements, above the 1,500 guideline. Large trees cost memory and CPU on every visitor's device.

    Flatten wrapper markup, render long lists virtually or paginate, and prefer semantic elements over nested divs.

    WSG 3.6: Ensure code follows good semantic practices

Where the bytes are

• JavaScript1.95 MB · 34 req
• Fonts285 kB · 6 req
• Images173 kB · 13 req
• HTML97 kB · 3 req
• CSS78 kB · 5 req
• Data (fetch)45 kB · 6 req
• Data (XHR)5.5 kB · 3 req