Website Carbon

Overview

The Website Carbon API estimates a website’s carbon footprint per visit — data transfer, energy use, and CO₂ per page load — from the Website Carbon Calculator methodology. Free and keyless in its early days; it now requires a free API key (verified 2026-08: requests without a key return 401 Unauthorised).

Quick Start

Get an API key (register at websitecarbon.com) then (replace YOUR_KEY):

curl "https://api.websitecarbon.com/site?url=example.com&key=YOUR_KEY"

{
  "url": "https://example.com",
  "green": true,
  "bytes": 2500000,
  "cleanerThan": 0.92,
  "statistics": {
    "adjustedBytes": 2500000,
    "energy": 4.17,
    "co2": { "grid": { "grams": 1.67 } }
  }
}

Authentication

• Register at websitecarbon.com → get a free API key.
• Send it as the key query parameter (missing key → 401 Unauthorised, verified).

Rate Limits & Notes

• Free tier has a daily request allowance (check the site — it’s modest); paid tiers scale.
• The response gives green (hosted on green energy?), bytes (page weight), cleanerThan (percentile vs other sites), and CO₂ estimates.
• It analyzes the URL server-side (fetches the page and its resources).
• Useful for eco-badges, sustainability dashboards, and performance-communication.

FAQ

Is Website Carbon free? There’s a free tier with a daily allowance; heavier use is paid.

How do I get a key? Register at websitecarbon.com — the key is in your dashboard.

What does it measure? Data transfer, energy per visit, and estimated CO₂ per page load.