Green Metrics Tool
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Measuring Websites

GMT can also measure websites and takes a multi-dimensional approach here:

  • The energy of the browser is measured to display and render the page
  • The network transfer energy is measured that was needed to download the HTML and page assets

By default the page is measured uncached. To isolate the render energy better GMT can optionally orchestrate a reverse proxy and warm up the cache by pre-loading the full page once before doing the final measurement. See Caching with a Reverse Proxy below.

Warning: Measuring websites is very tricky! GMT can shave off some of the caveats by using reverse proxys and cache pre-loading to make results more reliable. Since measurement load times are in milliseconds range you must have Metric Providers with very high sampling_rates connected. 2ms is a good value. Also website measurements are really only realiable in a controlled cluster with accuracy control.

Quick website measuring

Since measuring websites is so common GMT comes with a quick measurement function for that.

In the root folder you find the run-template.sh file.

Measure a sample query like this: bash run-template.sh website "https://www.green-coding.io"

It will download the needed containers, setup them up and run the measurement. This runs the example measurement file, which opens the page uncached. If you want the reverse proxy and the cache pre-loading instead, use the cached variant as your starting point.

Once you got this quick measurement running iterate on it by extending the file with more steps, for instance measuring all the sub-pages on your domain

Bonus tip: If you apply --quick to the run-template.sh call the measurement is quicker for debugging purposes. However results will be not as reliable. Use only for debugging!

Trying out our hosted service

We operate website-tester.green-coding.io as a simple demo vertical that uses the underlying Green Metrics Tool Cluster Hosted Service →.

Check it out if you do not feel like installing the GMT and just want to get carbon and energy info on a single page.

Crafting your own flows with Playwright commands

The Green Metrics Tool supports Playwright as a first-class command type in the usage_scenario.yml.
Playwright is a popular framework for end-to-end browser automation. With this integration, you can run browser-based user journeys directly inside your usage scenarios without maintaining a separate Playwright script file.

Simplified Setup with GMT Helper

Getting started with Playwright is easy using the !include-gmt-helper tag. By including gmt-playwright.yml, the Green Metrics Tool automatically:

  1. Configures the Playwright service container (gmt-playwright-nodejs) with the official Microsoft Playwright image.
  2. Installs all necessary Playwright libraries.
  3. Starts the Playwright browser and an IPC listener in the background.

Note that the helper is a YAML tag on the compose-file value — it is separated by a space and takes no colon. A minimal usage_scenario.yml looks like this:

name: "My website measurement"
author: "A wizard"
description: "Measures the home page of green-coding.io"

compose-file: !include-gmt-helper gmt-playwright.yml

# Your flow can now use the gmt-playwright-nodejs container
flow:
  - name: "Go to home page"
    container: gmt-playwright-nodejs
    commands:
      - type: playwright
        command: await page.goto("https://green-coding.io")
      - type: console
        command: sleep 5

This helper significantly simplifies your workflow by handling the setup for you.

Defining Playwright Commands

As shown above, you can define steps of type playwright in your flow.

  • type: playwright
    Defines a Playwright step instead of a shell command.
  • container: gmt-playwright-nodejs
    This must match the container provided by the GMT Playwright helper.
  • command: [str]
    A JavaScript/TypeScript snippet that is executed via Playwright inside the container.

This allows you to inline browser interactions alongside other commands for fine-grained measurement.

Caching with a Reverse Proxy

For scenarios where you want to cache browser requests to minimize network variability, use the gmt-playwright-with-cache.yml helper. It sets up an additional squid reverse proxy service and configures Playwright to use it.

name: "My cached website measurement"
author: "A wizard"
description: "Measures the home page of green-coding.io through a caching reverse proxy"

compose-file: !include-gmt-helper gmt-playwright-with-cache.yml

flow:
  - name: "Warmup and Caching"
    container: gmt-playwright-nodejs
    hidden: true
    commands:
      - type: playwright
        command: await gmtPlaywrightCache("https://green-coding.io", 5);

  - name: "Go to home page with cache"
    container: gmt-playwright-nodejs
    commands:
      - type: playwright
        command: await page.goto("https://green-coding.io")

The gmtPlaywrightCache(url, sleep) helper pre-loads the full page once so that the following steps are served from the proxy cache. Compare usage_scenario_cached.yml for a complete working example.

Full Example

Here is a complete usage_scenario.yml that measures the homepage of green-coding.io:

name: "Measure homepage of green-coding.io"
author: "A wizard"
description: "A simple example that measures the energy consumption of a website's homepage."

compose-file: !include-gmt-helper gmt-playwright.yml

flow:
  - name: "Navigate to green-coding.io"
    container: gmt-playwright-nodejs
    commands:
      - type: playwright
        command: await page.goto("https://green-coding.io")
        note: "Navigate to the website"
      - type: console
        command: sleep 10
        note: "Wait for 10 seconds to allow for idle load"

  - name: "Take a screenshot"
    container: gmt-playwright-nodejs
    commands:
      - type: playwright
        command: 'await page.screenshot({ path: "/tmp/repo/screenshot.png" })'
        note: "Take a screenshot to verify the page loaded"
Measuring AI/ML applications
Estimating Containers