Website Carbon

About Website Carbon

Website Carbon Calculator API is a REST API that measures the carbon emissions of any public web page. It accepts a URL via a GET request to the /v1/carbon endpoint and returns the page's transfer size, energy consumption, CO2 emissions in grams (calculated for both standard grid and renewable energy scenarios), a percentile ranking against other tested web pages, and a letter carbon rating from A+ to F.

The API works by loading and measuring the total data transfer size of a page (HTML, CSS, JavaScript, images, fonts, and third-party resources), checking the domain against the Green Web Foundation directory for renewable hosting status, and computing emissions using Version 4 of the Sustainable Web Design Model. Results are cached for 7 days per URL, with an optional parameter to force a fresh recalculation. First-time analysis of a page can take up to 30 seconds, while cached results return instantly.

It is intended for developers building website carbon calculators, sustainability dashboards, green web badges, or automated carbon auditing tools. Sandbox API keys return mock responses for testing, and each call to the endpoint counts as 2 API calls.

Key features

• Calculates CO2 emissions per page view for any public URL using Sustainable Web Design Model V4
• Checks green hosting status via the Green Web Foundation directory
• Assigns a letter carbon rating from A+ to F based on CO2 per page view thresholds
• Returns detailed statistics including transfer size, energy use, and grid vs. renewable CO2 comparisons
• Caches results for 7 days with an optional recalculate parameter to force a fresh analysis

Frequently asked questions