If you look after websites for clients, a short monthly carbon report is a useful habit. It shows the work you did, keeps page weight on the agenda, and gives the client something accurate to say if anyone asks. It also carries a risk: whatever you write may end up in the client's own marketing. So the report should be easy to read, and every line in it should be one you could back up.
A good test is the UK Competition and Markets Authority's Green Claims Code, which applies to claims about services as well as goods. Its six principles say claims must be truthful and accurate; clear and unambiguous; must not omit or hide important information; must make fair and meaningful comparisons; must consider the full life cycle; and must be substantiated. The CMA says the guidance isn't legal advice, and this article isn't either, but each section below maps onto one or more of those principles.
Which pages, and why
Start by listing the pages you checked and the reason for each. A small site might need three to five: the home page, the most visited service or product page, a typical blog post, and any page you changed this month. Keep the same set from month to month so the figures can be compared, and say so if you add or drop one.
One line of reasoning per page is enough: “Home page: most visits”, “Gallery: heaviest page”. That stops a client reading a single light page as a verdict on the whole site, which would fall foul of the “must not omit or hide” principle.
The figures, with method and date
For each page, give:
- Page weight in MB, and the date of the check.
- The estimate per page view in grams of CO₂e, with the method named: the Sustainable Web Design Model v4. GreenTracer measures one first, uncached load and uses the heavier of the mobile and desktop runs; say that too.
- The grade, with its band. The digital carbon ratings run from A+ to F, so “D (up to 0.278 g per view)” tells the client more than a letter alone.
- Hosting status, in the report's own words: the host is “listed as green by The Green Web Foundation”, or green hosting “could not be confirmed”. Don't upgrade either into something stronger.
If you're not sure what each figure means, how to read a website carbon report explains them. Attach the PDF of each GreenTracer report, so the client (or anyone they pass it to) can see where each number came from. That is the “substantiated” principle in practice.
What changed, and what it did
This is the part clients value most. List each change you made, the date, and the before and after figures from checks of the same page. An illustrative example on a standard host:
- Home page, before (2 October): 2.4 MB, about 0.355 g per view, grade E.
- Change: hero photo resized and converted to a modern format (9 October).
- Home page, after (10 October): 1.6 MB, about 0.237 g per view, grade D.
Check again after each change rather than waiting for month end, so each result can be tied to one change. GreenTracer doesn't re-check pages on its own; you run each check. When you check a saved page again, the report keeps the earlier checks as history, which gives you the before and after without a separate spreadsheet. Results vary a little between runs, so treat small movements with care; tracking improvements honestly covers how to compare like with like. Only compare figures worked out the same way: a number from a different tool or model isn't a fair comparison.
What the figure doesn't cover
Every report should carry the same short note of limits, because leaving them out could make the figure look more complete than it is. Something like:
- It is an estimate from data transferred, not a meter reading.
- It covers one first load of each page. The test doesn't scroll, click or accept cookie banners, so content that loads later isn't counted.
- It doesn't include building the site, staff using the admin area, emails, or the client's other operations. The Code asks claims to consider the full life cycle; a page-view figure is one slice of it.
- The model's authors say its broad boundaries mean it is likely to overestimate actual emissions.
What to leave out
- Absolute words. Don't call the site clean, neutral or sustainable. A lower estimate is a lower estimate.
- Unqualified “green”. The CMA says broad terms like this need solid justification. Say what was checked instead.
- Projected savings you didn't measure. Report the checks you ran. If you want a yearly figure, work it out openly using how to estimate your website's yearly carbon, and label it as an estimate.
- Rankings against other sites unless they were checked the same way, on the same day.
- Old results. GreenTracer shows a carbon result as out of date after 180 days; don't carry a stale figure forward.
Next actions, and a simple layout
End with two or three next actions, each tied to a page. Describe what you will change, not what it will save; the saving goes in next month's report, once measured. Then the report fits on one page:
- Pages checked and why.
- Per page: weight, grams per view, grade, hosting status, check date, method (SWDM v4).
- Changes made, with before and after checks.
- What the figure doesn't cover.
- Next actions.
- Attached: the PDF report for each page.
Keep the wording and layout the same each month, so the only things that change are the figures. Run the first set of checks to set the baseline.