If you are building a homework helper or a tutoring agent, the hard part of a physics question is rarely the arithmetic. It is the formula, the units and the steps a student can follow. Language models are good at explaining and still slip on numbers, so we gave our physics calculators a door that agents can call directly.

Since yesterday (3 November 2026) the UsePhysics MCP server is listed in the official MCP Registry as com.usephysics/physics-calculators . It is a remote server (Streamable HTTP), free, and it needs no key:

https://usephysics.com/api/mcp

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What is behind it

Four read-only tools:

tool what it returns

list_calculators every calculator: id, formula, input keys with units and defaults, page URL

calculate the results with units, the formula, the worked steps where the engine can derive them, and a link to the solved page

get_constant one CODATA 2022 constant as NIST prints it, with its uncertainty (or "exact") and the NIST…