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Shinsei method v1, October 2026

How we calculate

What the tool measures, how it works out the rating and where the figures come from. Everything is public and dated, so anyone can check.

This is a dated estimate, not a certification or a label.

  1. The measurement: Google Lighthouse loads the page like a visitor, on a simulated phone and on a computer, without scrolling or clicking.
  2. The footprint: Sustainable Web Design model v4, as in CO2.js: 0.30 kWh per GB transferred and 494 g of CO₂e per kWh (world average), for a first visit.
  3. The rating: the Sustainable Web Design A+ to F scale. It only depends on weight; hosting is a separate indicator.
  4. The comparison: real pages measured by HTTP Archive (July 2025).
  5. The good practices: 16 points checkable from the address, linked to the French RGESN 2024 framework and to the W3C guidelines. They are indications: the RGESN has 78 criteria, many of which need a human review.
  6. Over a year: the simulator multiplies the weight by your visits and uses the electricity of your visitors' country. The range shows the gap between published models: usage energy only at the low end, the former coefficient of 0.81 kWh per GB (model v3) at the high end. For comparison: the median web page from HTTP Archive, with the same traffic.

The rating scale

The rating depends only on the page weight, converted into grams of CO₂e for a first visit. The thresholds are those of the Sustainable Web Design model.

  1. A+Extremely lightup to 0.040 g
  2. AVery lightup to 0.079 g
  3. BLightup to 0.145 g
  4. CFairly lightup to 0.209 g
  5. DAverageup to 0.278 g
  6. EA bit heavyup to 0.359 g
  7. FHeavymore than 0.359 g

The 16 good practices

Each one is checked automatically from the page address, and linked to public standards when they cover it.

  1. 01Modern image formats

    At the same quality, WebP and AVIF images weigh much less than JPEG or PNG.

    References: RGESN 2024, criterion 5.1 · W3C WSG optimize media to reduce resource use · Green Software Foundation: “Serve images in modern formats”

  2. 02Compressed images

    An image can often lose weight with no visible difference.

    References: RGESN 2024, criterion 5.2 · W3C WSG optimize media to reduce resource use

  3. 03Right-sized images

    An image larger than its place on screen makes visitors download pixels nobody sees.

    References: RGESN 2024, criterion 6.4 · W3C WSG optimize media to reduce resource use · Green Software Foundation: “Properly sized images”

  4. 04Images loaded when needed

    Images further down the page can wait until the visitor gets close to them.

    References: W3C WSG defer the loading of non critical resources · Green Software Foundation: “Defer offscreen images”

  5. 05No autoplay

    A video or animation that starts on its own uses data, even if nobody watches it.

    References: RGESN 2024, criteria 4.1, 5.3 · W3C WSG optimize media to reduce resource use · W3C WSG ensure animation is proportionate and easy to control · Green Software Foundation: “Deprecate GIFs for animated content”

  6. 06Little unused code

    The browser downloads and reads code the page does not use.

    References: RGESN 2024, criterion 6.5 · W3C WSG minify and remove unused code · Green Software Foundation: “Remove unused CSS”

  7. 07Simple to display

    Beyond about 1,400 elements, the phone works harder to display the page (Google Lighthouse threshold).

    References: W3C WSG set goals based on performance and energy impact · Green Software Foundation: “Avoid an excessive DOM size”

  8. 08Few font files

    Each font file is one more download. Japanese fonts, in particular, are heavy.

    References: RGESN 2024, criterion 4.8 · W3C WSG use optimized web typography

  9. 09Files served by the site

    Fonts and libraries loaded from a public service (Google Fonts, jsDelivr…) add connections and report every visit to that service.

    References: RGESN 2024, criterion 6.7 · W3C WSG treat third parties the same as first parties

  10. 10Compressed text

    The server can send code and text compressed (Brotli or Gzip): they arrive much lighter.

    References: RGESN 2024, criterion 6.3 · W3C WSG reduce data transfer with compression · Green Software Foundation: “Enable text compression”

  11. 11Caching

    Files kept by the browser are not downloaded again on the next visit.

    References: RGESN 2024, criterion 6.2 · W3C WSG optimize caching and support offline access · Green Software Foundation: “Cache static data”

  12. 12Modern protocol (HTTP/2 or 3)

    HTTP/2 and HTTP/3 send several files at once over a single connection.

    References: W3C WSG ensure infrastructure fits project requirements

  13. 13No wasted requests

    A file that answers with an error or a redirect costs a round trip for nothing.

    References: W3C WSG audit and test for bugs or issues requiring resolution

  14. 14Third parties after a click

    Analytics, ads, social media and embedded videos often load on arrival, before the visitor has agreed.

    References: RGESN 2024, criterion 4.4 · W3C WSG treat third parties the same as first parties · W3C WSG promote responsible data practices · Green Software Foundation: “Avoid tracking unnecessary data”

  15. 15Mobile-friendly

    The page must fit the phone screen, without zooming.

    References: RGESN 2024, criterion 2.5 · W3C WSG ensure layouts work for different devices and requirements

  16. 16Transparency

    A carbon.txt file or a published eco-design statement shows what is done, and how.

    References: W3C WSG include expected and beneficial files · W3C WSG identify assess disclose review and mitigate sustainability impacts

Sources and licences

Calculation: CO2.js (Green Web Foundation, Apache-2.0 licence). Hosting: Green Web Foundation directory (ODbL licence). Comparison: HTTP Archive. Measurement: Google Lighthouse. Third parties: third-party-web (MIT licence).