laszlopere/mcp-gnu-units

mcp-gnu-units is an MCP server that gives AI agents precise, offline unit
conversion backed by the GNU units database. Convert between 3000+ units of
measurement — length, mass, time, temperature, area, volume, energy, power,
pressure, speed, data and more — evaluate compound unit expressions like kW*h
or acre*ft, reduce any quantity to its SI base units, search the unit database
by keyword, and look up the exact definition of any unit, prefix, or physical
constant. Deterministic, dimension-aware, and free of the hardcoded per-category
unit tables every other converter ships.
> **Status: feature-complete, pre-release.** All five domain tools ship —
> find_units, convert, convert_to_si, define_unit, and list_prefixes —
> alongside the info health check. Not yet published to PyPI; the remaining
> publish steps are tracked in TODO.
Distribution name: mcp-gnu-units · import package: mcp_gnu_units.
Built on GNU units
This project stands on the shoulders of
GNU units, the units-conversion program
written and maintained by Adrian Mariano for the Free Software Foundation. Its
database is the product of decades of careful curation — thousands of units,
physical constants drawn from CODATA and NIST, and the conversion semantics that
make dimensional analysis trustworthy. This server would not exist without it.
mcp-gnu-units bundles that database **verbatim** (see
Bundled data & provenance below) and pairs it with
an independent, pure-Python conversion engine, so every number it returns traces
straight back to GNU units' own definitions. It is offered in the same spirit
and under the same license (GPL-3.0-or-later). If you find this useful, the
original earns the credit first: .
Bundled data & provenance
This server stands on GNU units, Adrian
Mariano's units-conversion program, by bundling its unit database verbatim at
src/mcp_gnu_units/data/definitions.units. The conversion engine here is an
independent implementation; GNU units supplies the data.
- **Source:** GNU units 2.27 (tarball),
definitions.units data version 3.26 (2026-02-25).
- **License:** GPL-3.0-or-later © Free Software Foundation — the same license as
this project, so the two are wholly compatible.
- **Integrity:** the upstream tarball was GPG-verified (good signature from
Adrian Mariano) before the file was vendored.
Full attribution, version pins, and checksums are recorded in
NOTICE.
Sponsoring
mcp-gnu-units is free, open-source software developed in my spare time.