mcp-gnu-units is an MCP server designed to provide AI agents with precise, offline unit conversion capabilities, sourced from the GNU units database.
Purpose
This project addresses AI agents' needs for conversion and dimensional analysis involving units of measurement, enabling agents to obtain deterministic, traceable unit conversion results without relying on network access or built-in per-category unit tables.
Main capabilities
- Convert between more than 3000 units of measurement, covering categories such as length, mass, time, temperature, area, volume, energy, power, pressure, speed, and data.
- Evaluate compound unit expressions, such as kWh or acreft.
- Reduce any quantity to SI base units.
- Search the unit database by keyword.
- Look up the precise definition of any unit, prefix, or physical constant.
- Provides five domain tools: find_units, convert, convert_to_si, define_unit, list_prefixes, and the info health check.
- Runs offline, produces deterministic results, and is dimension-aware.
Usage
mcp-gnu-units is an MCP server for AI agents to call via the MCP protocol. The distribution name is mcp-gnu-units, and the import package name is mcp_gnu_units. The project has not yet been published to PyPI, and the publishing steps are recorded in the TODO. The specific installation commands, configuration methods, and usage examples are not given in the provided materials and are not yet available.
Technical foundation and data source
This server is built on GNU units. GNU units is a unit conversion program written and maintained by Adrian Mariano for the Free Software Foundation; its database has been carefully maintained for decades and contains thousands of units, physical constants from CODATA and NIST, and conversion semantics that make dimensional analysis trustworthy. mcp-gnu-units bundles the GNU units database verbatim at src/mcp_gnu_units/data/definitions.units, together with an independent pure Python conversion engine, so every value returned can be traced back to GNU units' own definitions. Bundled data source: GNU units 2.27 (tarball), definitions.units data version3.26 (2026-02-25). Integrity: before the file was incorporated into the project, the upstream tarball was verified via GPG (a valid signature by Adrian Mariano). Full attribution, version pinning, and checksums are recorded in NOTICE.
Applicable scenarios
Suitable for AI agent tasks that require precise, repeatable, traceable unit conversion and dimensional analysis, especially scenarios involving compound units, reduction to SI base units, and looking up definitions of units or physical constants.
Limitations and status
The project's current status is feature-complete, pre-release. All five domain tools are provided, but it has not yet been published to PyPI. The remaining publishing steps are recorded in the TODO. The materials do not state the specific supported platforms, runtime environment requirements, or performance limitations, and these are not yet available.
License
GPL-3.0-or-later. The bundled GNU units database is likewise GPL-3.0-or-later © Free Software Foundation; see NOTICE for details.
Sponsorship
mcp-gnu-units is free and open-source software, developed by the developer in their spare time. One-time or recurring sponsorship is available through GitHub Sponsors to support new features, bug fixes, and ongoing maintenance.
