How it works
Once a day, we ask the Green Web Foundation whether the host that serves your site runs on verified renewable energy.
When the Page weight check has run, we also estimate how much CO₂ each visit to your page emits, using the Sustainable Web Design model (version 4). It accounts for the energy used by data centres, networks and visitors' devices, and grades the page from A+ (cleanest) to F:
| Rating | CO₂ per visit |
|---|---|
| A+ | up to 0.040 g |
| A | up to 0.079 g |
| B | up to 0.145 g |
| C | up to 0.209 g |
| D | up to 0.278 g |
| E | up to 0.359 g |
| F | over 0.359 g |
The estimate is for a first visit, without the files a returning visitor already has cached.
Statuses
| Status | Meaning |
|---|---|
| OK | Your host is verified green. |
| Warning | Your host is not verified green, or the Green Web Foundation could not be reached. |
This check never fails, and by default you are notified of failures only, so it does not send alerts unless you change its notification level.
Fixing common problems
- Host not verified green: ask your hosting provider whether it runs on renewable energy and is registered with the Green Web Foundation, or move to a verified green host.
- Poor CO₂ rating: the estimate grows with the page weight, so every kilobyte you remove (images, scripts, fonts) improves the rating.