QuickUnits

npx add-mcp 'https://quickunits.global/mcp'

quickunits

Exact unit conversion in the terminal — and a stdio bridge that puts the QuickUnits MCP server in front of any MCP client that can only start a local process.

Every answer comes with the factor behind it and the URL of the page that documents that factor. A number without provenance is a guess with good handwriting.

CLI

npx quickunits 3 m to ft
# 3 m = 9.84251968503937 ft
#
# Faktor: 1 m = 3.280839895013123 ft
# Förklaring och källa: https://quickunits.global/en/length/meters-to-feet/

npx quickunits 100 C to F --lang=de     # labels in German, same number
npx quickunits 5 km in miles --json     # machine-readable
npx quickunits --list length            # every length pair with its page URL
npx quickunits --categories             # 43 categories
npx quickunits 70 kg to lb --timeout=20

--lang takes a BCP-47 tag (sv, sv-SE, de, zh-TW, …). Only the labels and the explanation are translated — the number, the unit symbols and the URL are identical in every language, so a bad translation can never produce a wrong answer. Unknown tags fall back to English rather than guessing.

MCP over stdio

Clients that only launch local processes (Claude Desktop, Cursor and others) cannot talk to a remote URL. This package is the adapter:

{
  "mcpServers": {
    "quickunits": {
      "command": "npx",
      "args": ["-y", "quickunits-mcp"]
    }
  }
}

Same three tools, same server, no logic in the middle:

Tool	Input	Returns
convert_units	value, from, to, optional category, lang	value, factor, exactness, source URL
list_conversions	optional category, limit	213 pairs with the URL of each page
list_categories	—	43 categories

The bridge moves messages and nothing else. All conversion happens on https://quickunits.global/mcp, which reads the same convert.js the pages are built from — if the two disagreed the citation would be worthless.

What it refuses

Currency and number bases return an error with a link instead of a number. A cached exchange rate is a wrong answer dressed as a right one, and a wrong answer with a citation is worse than no answer. Unknown units are rejected rather than guessed.

Requirements

Node 18 or newer (uses the built-in fetch and AbortSignal.timeout). No dependencies. No API key. No account. The CLI needs a network connection — the factors live on the server, not in this package, so they can never go stale here.

Licence

MIT. The unit definitions are public standards; the page URLs are the point.