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: https://www.gnu.org/software/units/.

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. Sponsoring keeps this project alive and actively maintained — it funds new units-engine features, bug fixes, and ongoing support, and it's a direct signal that the work is worth continuing.

If the project is useful to you, please consider sponsoring it through GitHub Sponsors. Click the Sponsor button at the top of the repository, or visit the link directly, and pick a one-time or recurring tier. Every contribution, large or small, is hugely appreciated and goes straight back into keeping mcp-gnu-units healthy.

License

GPL-3.0-or-later. See LICENSE. The bundled GNU units database is also GPL-3.0-or-later © Free Software Foundation; see NOTICE.