#nist

Atomic isotope reference data as an API, built on the NIST Atomic Weights and Isotopic Compositions. For every known nuclide: its element (atomic number Z and symbol), mass number, relative atomic mass, natural isotopic composition (abundance) and the element's standard atomic weight. Look an isotope up by label (C-12, U-238) or by symbol + mass, list every isotope of an element, rank isotopes by mass or natural abundance, or search. A precise physics and chemistry reference for science, education, lab and engineering apps. Distinct from element-level data.

api.oanor.com/isotopes-api

The NIST CODATA 2022 fundamental physical constants as an API — 355 quantities used throughout physics and engineering. Look up any constant by name or slug (e.g. speed of light in vacuum → 299792458 m/s, exact; Planck constant, elementary charge, Avogadro constant, Boltzmann constant, Newtonian constant of gravitation), search by keyword, or list them all. Each record carries the recommended value, the standard uncertainty, the SI unit and whether the value is exact (by definition since the 2019 SI redefinition). Ideal for scientific calculators, physics/engineering software, education and lab tooling.

api.oanor.com/constants-api