121 mathematical, physical, and cryptographic constants for Rust — no_std, WASM, compile-time const, typed runtime lookup, datetime, 15 macros, MIT/Apache-2.0

C++20 header-only library that catches unit mismatches at compile time. SI units, 140+ literals, physical constants — zero runtime overhead.

Look up countries, timezones, periodic table elements, physical constants, units, HTTP status codes, and MIME types via MCP. STDIO or Streamable HTTP.