CO2 Offset API vs WattFigure API

Two free Environment APIs compared on access, reliability and developer ratings, using data from our daily health checks.

The verdict

Choose CO2 Offset API if its data fits your use case better; on access and reliability it's level with WattFigure API.
Choose WattFigure API if you want to call it from browser JavaScript, faster responses.

	CO2 Offset API	WattFigure API
What it does	API calculates and validates the carbon footprint.	US electricity rates by state, with appliance and EV charging running costs.
Provider	Corrently IO	WattFigure API
API key	Not needed	Not needed
HTTPS	Yes	Yes
CORS (browser calls)	Unknown	Yes
Status today	Online · 1414 ms	Online · 712 ms
Uptime (30 days)	Up	Up
Developer rating	Not rated yet	Not rated yet
Price	Free / free tier	Free / free tier

API calculates and validates the carbon footprint.

Service Rahmenwerk zur Bestimmung, Berichterstattung und Kompensation der Treibhausgasemissionen für...

Strengths

US electricity rates by state, with appliance and EV charging running costs.

Strengths

Prototyping or a tutorial? Pick the one that needs no API key (both qualify).
Calling from a web page? You need CORS. Otherwise route requests through your own server or a serverless function.
Going to production? Favour HTTPS, a strong uptime record and a provider with clear rate limits and terms. Check each API's docs before you commit.
Still unsure? Both are free to try: send one request to each and compare the data you get back.

Neither needs an API key; you can call both straight away.

WattFigure API supports CORS, so front-end JavaScript can call it directly. Call the other from a server.