● Live · 2026 edition
The emission-factor API that ships its own audit trail.
16,686 sourced emission factors and seven audit-traced calculation engines, over HTTPS and MCP. Every value comes back with the exact place in the source it was read from, pinned to a data version — and a public URL your auditor can open to check it.
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16,686 factors · verify one yourself · 158 methodologies · public DOIs · free tier, no card, then US$49/mo
$ curl "api.greencalculus.com/v1/factors?search=grid.gbr.location_based" { "meta": { "gc_version": "2026.203", "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" } }] }
$ curl api.greencalculus.com/v1/calculate/electricity \ -H 'Authorization: Bearer gc_live_…' \ -d '{"consumption":{"value":250000,"unit":"kWh"}, "location_factor_key": "grid.gbr.electricity.location_based"}' { "location_based": { "emissions": { "value": 32740, "unit": "kg CO2e" }, "formula": "250000 kWh × 0.13096 = 32740 kg CO2e", "factor": { "source": { "id": "DEFRA_2026", "cell_ref": "'UK electricity'!E25" } } }, "scope": { "ghg_protocol": "scope2" }, "receipt": { "algorithm": "sha256", "id": "gcr_…" } } // abridged — the wire carries both Scope 2 methods
# claude_desktop_config.json — 12 tools { "mcpServers": { "greencalculus": { "url": "https://mcp.greencalculus.com" } } } > lookup_factor( "grid.gbr.electricity.location_based") { "factor": { "value": 0.13096, "unit": "kg CO2e per kWh" }, "provenance": { "source_id": "DEFRA_2026", "cell_ref": "'UK electricity'!E25" }, "proof_urls": [ "verify.greencalculus.com/…@2026.203" ] } // 2 of the 12 tools need no key
Questions people ask, answered
All 31 questions- ChoosingWhat API should I use to get emission factors?Run five tests in ten minutes: time to first number, provenance in the response, reproducing last year, the licence, and what the vendor admits it lacks.
- ChoosingWhich emission factor database should I use in 2026?Choose by licence first, then coverage: nearly half the sources we reviewed may not be passed on. Check for non-commercial, share-alike and purpose limits.
- ChoosingWhat are the alternatives to Climatiq for emission factor data?For an API: GreenCalculus, Carbon Interface or the publishers' own files. Climatiq's published plans exclude API access and its free tier is non-commercial.
- Looking upWhich emission factor datasets can I legally redistribute in a product?DEFRA, EPA, IPCC, Ember and ADEME with attribution; EXIOBASE share-alike; SBTi and PCAF non-commercial; IEA and standards bodies not at all. Every source ruled.
- Looking upWhere can I download emission factors as a dataset I can use commercially?DEFRA, EPA, IPCC and ADEME with attribution; EXIOBASE and Ember under share-alike. SBTi and PCAF are non-commercial; IEA and ecoinvent are closed.
- ComplyingWhere do I get CBAM default values for a system?Annex I of Regulation (EU) 2026/1740: 1,533 country by CN-code base values you mark up yourself. Annex II is IEA data nobody may redistribute.
- ComplyingFor CSRD reporting, which emission factor source should we standardise on?None. ESRS E1 names no database; standardise on a hierarchy, one default source per category, recorded with its edition and reviewed each year.
- ComplyingWhat data do I need for PCAF financed emissions reporting, and where from?Four buckets per asset class: exposure, the attribution denominator, the counterparty's emissions or activity, and the metadata behind the quality score.
- DoingHow do I get the UK electricity emission factor in Python?Read it from the GreenCalculus API with the standard library and no account; the response carries the DESNZ 2026 value, its source cell and data version.
- DoingHow do I get DEFRA conversion factors into my software automatically?Read them from the GreenCalculus API by section or key, pin as_of, and let each June release land as a new data version. 1,453 rows, checked cell by cell.
- ChoosingWhere do I source the emission factors for a freight calculator?GLEC v3.2 tonne-km factors for road, rail, sea and air, DEFRA's delivery-vehicle rows for UK fleets, and ISO 14083 as the boundary rule, all served by API.
- DoingHow do I stop an LLM inventing emission factors in my product?Never let the model produce the number: retrieve from a sourced corpus, constrain output to a real factor key, return the citation, and let it say not held.
Check 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 →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%
of AI answers 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%
of correctly-cited AI answers were still 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
models 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 line in the source.
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 place it was read 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 source 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 v2026.203. https://doi.org/10.5281/zenodo.20612874
What this format isOn 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. Keys, names, units, publishers and licences are open; the values are served by the API and are not offered as a bulk download.