Gnomon MCP

What lihtness/gnomon-mcp MCP server does

The lihtness/gnomon-mcp MCP server gives agents deterministic utilities for dates, calendars, arithmetic, and unit conversion. It is intended for cases where approximate reasoning can produce an incorrect answer, such as calculating elapsed time, adding months across calendar boundaries, evaluating decimals, or converting physical quantities.

The server exposes a standalone now tool that returns an 18-field snapshot of the current moment. The result includes ISO time, date and clock fields, Unix time, timezone, weekday information, day-of-year, ISO week, quarter, US government fiscal year, and a weekend flag. A timezone can be supplied.

How it works

MCP clients communicate with the server over standard input and output. The calendar tool accepts a list of operations and returns results in the same order, allowing one request to process multiple rows or unrelated date calculations. Supported operations include diff, until, since, add, weekday, business_days, parse, and format.

Date inputs can be known timestamps or natural-language expressions such as “next Thursday” and “in 3 hours.” Difference and elapsed-time operations support seconds, minutes, hours, days, and weeks. Calendar-aware month and year addition are available through add. Business-day counting covers Monday through Friday, with the start date included and the end date excluded.

The calc tool also accepts a list and evaluates Python expressions in order. Common math functions and constants, statistical functions such as mean and median, and selected built-ins including sum, range, sorted, min, and max are preloaded. calc_convert uses Pint for conversions such as meters to feet, kilograms to pounds, and Celsius to Fahrenheit.

Setup and configuration

The recommended launch command is:

uvx gnomon-mcp

This runs the package on demand without a separate installation. The package can alternatively be installed with pip install gnomon-mcp, after which the gnomon-mcp executable can be used directly. The repository also documents a --demo mode that invokes each tool once and prints results without requiring an MCP client.

The README includes configuration examples for Claude Code and Claude Desktop. No API key, account credential, or environment variable is specified for operation.

Tools and capabilities

• now(tz?): returns the current-time snapshot.
• calendar(ops): batches date calculations and formatting operations.
• calc(expressions): evaluates multiple Python expressions.
• calc_convert(value, from_unit, to_unit): converts quantities with Pint.

Batch input is useful for applying the same kind of calculation to every row in a table while preserving result order. The lihtness/gnomon-mcp MCP server combines date, math, and unit functions behind one MCP connection rather than requiring separate utility servers.

Limitations and notes

The business-day operation excludes weekends but does not account for public holidays. The README describes calc as float-based and notes that it is not suitable for currency calculations requiring decimal arithmetic and explicit rounding. Proposed features such as holiday-aware calendars, regex processing, token counting, hashing, and cron support are not implemented tools in the current server.