● Live · 2026 edition
The emission-factor API that ships its own audit trail.
16,673 sourced emission factors and seven audit-traced calculation engines, over HTTPS and MCP. Every value comes back with the exact source cell it was read from, pinned to a data version — and a public URL your auditor can open to check it.
Find a factor
Try
16,673 factors · 16,673 source cells · 158 methodologies · public DOIs · no black boxes
$ curl "api.greencalculus.com/v1/factors?search=grid.gbr.location_based" { "meta": { "gc_version": "2026.189", "total": 1 }, "factors": [{ "key": "grid.gbr.electricity.location_based", "factor": { "value": 0.13096, "unit": "kg CO2e per kWh" }, "source": { "id": "DEFRA_2026", "cell_ref": "'UK electricity'!E25" } }] }
Measured, not asserted
A confident citation is not a correct number.
We put 467 emission-factor questions to five frontier models, scored the answers against the published values, and released the questions, the scorer and the results with a DOI.
46.3%
landed within 10%
Across 45 sections and 75 publishers. Textbook fuels scored 92%; jurisdiction-specific and recent factors fell to single digits — which is exactly where reporting deadlines live.
55%
cited right, answered wrong
Models named a source 75% of the time, and named the correct one in 90% of those. Then 55% of those correctly-attributed answers still carried the wrong number.
0 of 5
knew this server existed
Asked whether an MCP server for carbon data exists, all five said no established one does — while ours has been in the official MCP registry since 12 August 2026.
Agent-native
Point your agent at one URL. Get numbers it can cite.
Point Claude — or any MCP client — at mcp.greencalculus.com and your agent can resolve the right factor from a plain description, then run any of seven audit-traced calculations mid-conversation — handing back the source, the version, and a tamper-evident receipt with the answer. Two of those tools — search_factors and explain_absence — answer with no key at all, so an agent can search the corpus, and be told why a factor is not held, before anyone signs up.
# 12 tools: lookup_factor · lookup_factors · search_factors · resolve_factor · explain_absence · calculate_activity · calculate_pcaf · calculate_embodied · calculate_electricity · calculate_freight · calculate_spend · calculate_business_travel
{
"mcpServers": {
"greencalculus": {
"url": "https://mcp.greencalculus.com",
"headers": { "Authorization": "Bearer gc_live_…" }
}
}
}
Why GreenCalculus
Every number is traceable — down to the source cell.
Most carbon tools hand you a figure and bury where it came from. We hand you the figure and its provenance: the source, the exact cell it was transcribed from, the licence, and a pinned data version — so a person can cite it and a machine can reproduce it in an audit.
- ✓ Named source + exact cell reference on every value
- ✓ Version-pinned & DOI-published — reproducible for years
- ✓ Open methodology — the math is shown, never a black box
GreenCalculus. Grid Electricity Emission Factors by Country. MasterBrain v2026.189. https://doi.org/10.5281/zenodo.20612874
What this format isCheck us before you pay us
Every number the API returns has a public page.
The API has two halves, and each one has a human surface open to anyone — no account, no key. The calculators run the same engines. The library is the same corpus, open to read.
The engines, runnable by hand
142 audit-grade calculators plus quick tools and unit converters — the same seven engines the API runs, with a form in front of them. Every result traces to a versioned factor.
Open the calculators →The corpus, open to read
The standards we encode, the methodologies we document, the glossary, and the datasets behind every number — citable to MasterBrain, with DOIs, and browsable without a key.
Open the library →On the other side of this market?
Consultancies, verifiers and carbon software reach buyers here at the moment they have just run the numbers — through a listing in the curated directory, a sponsored calculator category, or a licence to the data and API. All commercial options →
Built on public-domain & open data from
Published where you can check it
Build carbon numbers you can defend.
1,000 calls a month, every calculation engine, commercial use with attribution. No card. Or browse the whole corpus without an account at all.