Discovery / health-check entrypoint: report availability and version info.

Returns seven keys: status ("available"), name, version (package version), python (runtime version), mcp_sdk (MCP SDK version, or "unknown"), toolsets (empty until the GNU units engine lands), and units_db — the bundled GNU units database's source, data_version, and data_updated (§2.4.6 / §5.4), read from the shipped file's own header so it can't drift. Example: {"status":"available","name":"mcp-gnu-units","version":"0.0.1", "python":"3.12.3","mcp_sdk":"1.28.0","toolsets":[], "units_db":{"source":"GNU units","data_version":"3.26","data_updated":"2026-02-25"}}

Search the GNU units database for units whose name or definition contains a keyword.

Basic substring search over the 3000+ unit GNU units database (TODO §14.1). A hit is any unit whose name OR definition text contains query (case-insensitive); prefixes are excluded. Results are returned in the database's native order and capped at limit. Use this to discover the exact spelling of a unit before calling a conversion tool.

Returns: query (echoed), count (number of results returned), and results, a list of objects each carrying:

• name : the unit's name.

• definition : its definition text (the source line with the leading name token removed, so the name is not repeated).

• kind : "unit" | "primitive" | "function" | "table".

• dimension : the unit reduced to base-unit signature, e.g. "kg m^2 / s^3" for power — use it to check whether two units are conformable without a second call. Omitted for hits that do not reduce (functions, tables).

• base_value : the unit reduced to base/primitive units, coefficient included, e.g. "745.699 kg m^2 / s^3". Omitted alongside dimension when the hit does not reduce.

Enriching each hit lets you search AND triage in a single call instead of a follow-up lookup per unit. Example: find_units("horsepower") -> {"query":"horsepower","count":9,"results":[{"name":"horsepower", "definition":"550 foot pound force / sec","kind":"unit", "dimension":"kg m^2 / s^3","base_value":"745.7 kg m^2 / s^3"}, ...]}

Convert a value or unit expression from one unit to another (GNU units engine, TODO §16).

The universal conversion core: one tool covers every category (length, mass, time, temperature, area, volume, energy, power, speed, data, …) plus compound expressions like kW*h or acre*ft. Linear conversions return the ratio of coefficients; a nonlinear target (e.g. tempF) applies that unit's inverse.

Returns: from and to (echoed), result (the converted magnitude WITH the target unit, e.g. "1.609344 km" — the primary human-readable answer), value (the same magnitude as a bare float for programmatic use), and exact (true when the result is exact, false when it was rounded). Errors cleanly (isError) when a unit is unknown, an expression is malformed, or the two sides are not conformable. Example: convert("1 mile", "km") -> {"from":"1 mile","to":"km","result":"1.609344 km","value":1.609344,"exact":true}

Reduce a value or unit expression to its SI base units (GNU units engine, TODO §17).

Rewrites any expression in terms of the database's primitive/base units — kg, m, s, A, K, mol, cd, and the like — collapsing all derived and prefixed units. This is how you see what a quantity really is dimensionally: kW*hour becomes 3600000 kg m^2 / s^2 (3.6 MJ), newton becomes 1 kg m / s^2. Use it to compare or sanity-check units, or to get a magnitude in coherent SI.

Returns: expr (echoed), result (the reduced quantity WITH its base-unit signature, e.g. "3600000 kg m^2 / s^2" — the primary human-readable answer), value (the same magnitude as a bare float for programmatic use), dimension (just the base-unit signature, e.g. "kg m^2 / s^2", or "1" when dimensionless), and exact (true when the result is exact, false when it was rounded). Errors cleanly (isError) when a unit is unknown, an expression is malformed, or it is a nonlinear unit with no linear base form (e.g. tempF). Example: convert_to_si("kWhour") -> {"expr":"kWhour","result":"3600000 kg m^2 / s^2","value":3600000.0, "dimension":"kg m^2 / s^2","exact":true}

Show a single unit/prefix/constant's definition, kind, dimension, and base value (TODO §13).

Looks up one name in the GNU units database and reports exactly what it is and what it reduces to — the inspect/"define" counterpart to convert. Works for ordinary units, SI/binary prefixes, physical constants, nonlinear function units (tempF), and piecewise tables (brwiregauge).

Returns an object with:

• name : echoed.

• kind : "unit" | "primitive" | "prefix" | "function" | "table".

• definition : the database definition text (source line, leading name token removed). "!" marks a primitive/base unit.

• dimension : base-unit signature, e.g. "kg m^2 / s^3" for power; "1" when dimensionless. Omitted for hits that do not reduce.

• base_value : the unit reduced to base units with its coefficient, e.g. "745.699871582 kg m^2 / s^3". Omitted alongside dimension.

• function : for nonlinear units only — {signature, input_dimensions, output_dimension} describing the conversion function.

Errors cleanly (isError) when the name is not defined in the database. Example: define_unit("newton") -> {"name":"newton","kind":"unit","definition":"kg m / s^2", "base_value":"1 kg m / s^2","dimension":"kg m / s^2"}

List every SI and binary prefix in the GNU units database with its multiplier (TODO §13).

Enumerates all defined prefixes — the SI decimal ladder (quetta…quecto and their symbols Q…q) plus the binary/IEC prefixes (kibi/Ki, mebi/Mi, …) — sorted by descending magnitude. Useful for discovering the exact prefix spelling to use in a convert or convert_to_si expression, or for seeing a prefix's exact numeric value.

Returns: count (number of prefixes) and prefixes, a list of objects each with name (the prefix, without its trailing hyphen) and multiplier (its value as a string, exact where the value is an exact integer, e.g. kibi -> "1024", mega -> "1000000"). Example: list_prefixes() -> {"count":125,"prefixes":[{"name":"quetta","multiplier":"1000000000000000000000000000000"}, ...,{"name":"kibi","multiplier":"1024"}, ...]}