Is there an open-source or cheaper alternative to commercial carbon data APIs?

Run this before you read anything else. No account, no key, no email:

curl "https://api.greencalculus.com/v1/factors?search=diesel&limit=1"

That returns a real emission factor with its source, its cell reference and its licence attached. It is one of two APIs on this page that will answer a stranger with no signup at all. The rest mean something else by free — and for two of the best-known names, “free” explicitly excludes using the data in anything that earns money.

Four different things called “free”

Every roundup puts these in one column. They are not one thing, and the differences decide whether you can ship.

The fourth category is why “free” and “usable in my product” are separate questions, and why the table below asks them separately.

The comparison

Verified against each vendor’s own pricing page, docs or terms on 8 September 2026. Where a vendor does not publish a figure, this says so rather than guessing.

The non-commercial trap

Two of the most recommended free tiers in this category are licensed for non-commercial use only, and you will not learn that from the signup form.

Climatiq’s free Starter plan is labelled “Non-commercial license” on its pricing page, and its terms are explicit: the services are to be used “exclusively internally, for the purpose of calculating emissions or climate impact assessment for reporting and/or disclosure”, and users are “explicitly prohibited from using… the Services… for purposes primarily related to or directed towards commercial advantage or monetary compensation.” Attribution is required on every tier, paid included: you are “obliged to disclose the original source of each data point”.

WattTime’s free access runs under a Noncommercial Agreement whose wording is equally clear — the licensee “may not use the WattTime Data for any commercial application such as to develop competing products or generate profit” — with eligibility limited to individual, research, academic, education and non-profit use.

Neither is a criticism of those products; both are reasonable positions for the vendor to take, and both are properly documented if you go and read the terms. The problem is that every listicle prints them in a column headed “Free” next to genuinely open options, and a developer prototyping on a free key can be six months into a commercial build before anyone reads the licence. If that is the position you are in with Climatiq specifically, our field guide to the alternatives sorts the whole category and says plainly when the answer is to stay.

What you may do with what you get back

Three questions decide whether an API fits a product, and the answers are rarely on the pricing page.

May you cache or store the results? Almost every real integration caches, and the terms often address this obliquely if at all. Climatiq’s terms bar extracting, exporting or scraping content “for use outside of the agreed contractual purpose”. Patch’s terms bar systematic retrieval and republication without written consent. Carbon Interface’s terms of use cover the website and user content but say nothing about the estimates the API returns — which is silence, not permission.

Must you attribute, and where? Ember and Climate TRACE both require credit under CC BY 4.0. Climatiq requires source disclosure on all tiers. Where products get caught is placement, not wording: an attribution on a settings screen does not travel with an exported CSV, and the export is what your customer forwards to their auditor.

May you pass the values on? Redistribution is the right that separates a data licence from a data subscription. CC BY 4.0 sources — Climate TRACE, Ember — permit it with credit. Most commercial APIs do not grant it at any published tier, ours included below Business.

One caveat on the most open option here. Climate TRACE’s own inventory is CC BY 4.0, but its terms also note the dataset reproduces material from twelve named external sources — including commercial entity-identifier services — and state that it is “the sole responsibility of the user to review the terms and conditions for all the above sources.” So “Climate TRACE is CC BY 4.0, ship it” is right about their data and incomplete about everything travelling with it. Ember publishes upstream data from other bodies under its own blanket CC BY 4.0 with no such carve-out stated, which is cleaner — though silence is not the same as a guarantee.

Dead ends other lists still recommend

Four things worth knowing before you follow an older roundup.

Climate TRACE’s older endpoints are stale. Widely copied v4 and v6 paths return errors; the current API is v7, and the country-emissions path most examples use has moved. Working paths include /v7/sources/emissions, /v7/rankings/countries and /v7/definitions/sectors. It is also explicitly a beta API, so treat availability accordingly.

Patch and Cloverly are not what the lists describe. Both are carbon-credit procurement platforms rather than emission-factor APIs, and both have moved away from self-serve developer positioning — neither publishes a price, and the route in is a sales conversation. Their APIs still answer; the companies around them changed.

“cli.im” is not a carbon API. It appears on more than one aggregated list. It is a Chinese QR-code generator. This is what happens when lists are assembled from other lists.

Us, in the same columns

We are on this page, so here is our own entry written to the same standard, including the parts that do not flatter us.

Genuinely keyless. Six routes take no key and no account, and return full values rather than redacted previews: corpus browse and search, release status, the change feed, the coverage matrix, the roadmap, and the absence register — the last being a list of things we don’t have, which is not a normal thing to publish. Every response carries a licences block naming the licence, redistribution status and basis of each source behind the rows, so the terms arrive with the data. The licence of every source behind them is published in full.

curl "https://api.greencalculus.com/v1/factors?search=diesel&limit=1"
curl "https://api.greencalculus.com/v1/coverage"
curl "https://api.greencalculus.com/v1/absence?limit=5"

The free key. 1,000 calls a month at no cost, 30 requests a minute. Commercial use inside your own application is permitted — there is no non-commercial clause in our terms at any tier. The calculation endpoints run on every tier including Free.

What free does not include. Redistribution is not granted below the Business plan, so you may compute with our data but not serve it onward to your own customers. The bulk corpus feed is a Business feature. Attribution is required on Free and Developer. And our terms bar using the open endpoints to reconstruct the corpus in bulk — the keyless routes are a way in, not a loophole, and we would rather say that plainly than pretend not to notice.

The honest gap. The bulk feed carries the 91 sources whose licences permit redistribution, not all 167 in the corpus. The remainder are citable and usable in calculations but cannot be handed over, because we do not have that right ourselves. Why that is, and which datasets it affects, is the subject of the companion guide on the database landscape.

Picking one

By what you are actually doing, rather than by feature count.

Frequently asked questions