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Measurement methodology (simplified)

This document explains, in plain terms, how the tool estimates the weight of a website.

Big picture

Measuring the "weight" of a website is complex. Modern sites load resources over time, may prefetch pages, and behave differently depending on the user journey. The result produced by this tool is therefore an estimate, based on the pages and actions you chose to test.

This is especially true for SPA (Single Page Application) sites: internal navigation does not reload everything, so the measured weight strongly depends on the actions performed.

What the tool measures

For each step in the journey, the tool observes:

  • requests triggered by the action (click, navigation, wait),
  • the amount of data downloaded,
  • the final page URL after the action,
  • an EcoIndex score estimated from these elements (not necessarily identical to the official EcoIndex result).

The tool follows a user journey defined in a journey.js file and measures what happens during each step.

Technical overview (brief)

  • Measurement window per step: from action start to settling + delay + scroll.
  • request_count: number of requests observed within the window.
  • compressed_kb: transferred size (compressed bytes).
  • decompressed_kb: estimated via ResourceTiming when possible, with fallback.
  • dom_nodes: GreenIT method (excluding svg descendants).
  • EcoIndex: computed from observed values (estimate).

How to interpret the results

  • The output is not the absolute total weight of the whole site.
  • It represents the weight of the tested journey.
  • Changing pages or actions will change the measurement.

In other words, the tool provides a representative snapshot of a journey, not a single definitive number for the entire site.

Important limitations

  • Untested pages are not included.
  • SPAs can hide part of the downloads (prefetch, cache, internal navigation).
  • Network conditions, hardware, and site versions can influence the measurement.

Sources

The tool relies on EcoIndex methodology for the environmental score: