GreenCalculus MCP server

Sourced greenhouse-gas emission factors and audit-traced carbon calculations, as an MCP server. Every value comes back with its exact source cell and a pinned data version — so an agent hands back a number a person can cite and a machine can reproduce, instead of a guess.

Do you need this package?

Probably not. The server is remote, and if your client speaks remote MCP you should point it straight at the URL — nothing to install, nothing to update:

config.json

{
  "mcpServers": {
    "greencalculus": {
      "url": "https://mcp.greencalculus.com",
      "headers": { "Authorization": "Bearer YOUR_KEY" }
    }
  }
}

This package exists for the clients that can only spawn a local stdio process, and for docker run installs. It is a thin bridge: it forwards each JSON-RPC message to the remote server and returns the reply verbatim. No method is special-cased, so new tools appear here without a release.

Use it over stdio

config.json

{
  "mcpServers": {
    "greencalculus": {
      "command": "npx",
      "args": ["-y", "greencalculus-mcp"],
      "env": { "GREENCALCULUS_API_KEY": "YOUR_KEY" }
    }
  }
}

Or with Docker — -i is required and -t must be omitted, because the container's stdin/stdout are the transport and a TTY corrupts the stream:

config.json

{
  "mcpServers": {
    "greencalculus": {
      "command": "docker",
      "args": ["run", "-i", "--rm", "-e", "GREENCALCULUS_API_KEY", "greencalculus/mcp"],
      "env": { "GREENCALCULUS_API_KEY": "YOUR_KEY" }
    }
  }
}

Get a free key at https://greencalculus.com/developers — no card. Discovery (initialize, tools/list) works without one, and so do search_factors and explain_absence; every other tool needs a key.

Tools

Tool	What it does
`lookup_factor`	Fetch one emission factor by key, with its source and version
`lookup_factors`	Fetch many factors by key in one call — a portfolio is one request, not one per factor
`search_factors`	Search the corpus by free text
`resolve_factor`	Map a messy real-world description to the best-matching factor
`explain_absence`	Say why a factor does not exist, rather than returning nothing
`calculate_activity`	Activity → emissions, with unit conversion and GHG Protocol scope
`calculate_electricity`	Location-based and market-based electricity
`calculate_embodied`	Embodied carbon (EN 15978), explicit about missing lifecycle stages
`calculate_pcaf`	PCAF financed emissions, with the audit trail
`calculate_freight`	Freight by mode, distance and load
`calculate_spend`	Spend-based EEIO
`calculate_business_travel`	Business travel across modes

Configuration

Variable	Default	Meaning
`GREENCALCULUS_API_KEY`	—	Your API key. `GC_API_KEY` is accepted as an alias; the explicit name wins.
`GREENCALCULUS_MCP_URL`	`https://mcp.greencalculus.com`	Override the endpoint.
`GREENCALCULUS_MCP_TIMEOUT_MS`	`120000`	Per-request timeout.

Diagnostics go to stderr. Nothing but JSON-RPC is ever written to stdout — a stray byte there corrupts the session.

Develop

Terminal

npm test                      # unit tests, no network
node bin/greencalculus-mcp.js # reads JSON-RPC on stdin
docker build -t greencalculus/mcp .

Releasing

Bump version in package.json, merge to main. That's the whole procedure.

release.yml asks npm and the MCP registry whether they already have that version and publishes only where they don't, so a merge that bumps ships it and a merge that doesn't is a no-op. It also runs weekly, so a publish that failed is retried without a new commit.

server.json is the registry manifest, and the workflow rewrites its version from package.json before publishing — one source of truth, three places that have to agree.

npm authenticates by trusted publishing, so there is no npm token here. The registry needs one secret, and the reason is worth knowing: we publish as com.greencalculus/api, a DNS namespace, and GitHub OIDC only ever grants io.github.<org>/*. So the registry step signs with the key matching the v=MCPv1 TXT record on greencalculus.com, held as MCP_PRIVATE_KEY. scripts/rotate-registry-key.sh generates a fresh pair and installs it without ever printing the private half; it prints the TXT record to publish. Without the secret the registry step skips and says so — npm still publishes.

Also available

REST API and docs — https://greencalculus.com/developers
Client SDKs (Python, JS/TS) — https://github.com/greencalculus/greencalculus-sdk
Official MCP registry — com.greencalculus/api
Smithery — https://smithery.ai/servers/greencalculus/api

Licence

MIT — see LICENSE. The licence covers this bridge. Emission-factor data returned by the API carries the licence of its underlying source, which is named in every response.