GMol

Parse chemical formulas (with underscore subscripts, e.g. H_2O, Fe_2(SO_4)_3) and compute molar masses. Works in Node and the browser. Includes a CLI.

Install

npm i gmol
# or
pnpm add gmol

Usage (Library)

import { molarMass, parseFormula } from "gmol";

const { counts, molarMass: mw } = molarMass("Fe_2(SO_4)_3");
console.log(counts); // { Fe: 2, S: 3, O: 12 }
console.log(mw); // ~399.88

Browser

The package has no Node-only APIs, so you can import it in bundlers (Vite/Next/Webpack) and use it client-side.

API

• tokenize(formula: string): Token[]
• parseFormula(formula: string): ElementCounts
• computeMolarMass(counts: ElementCounts, weights?: Record<string, number>): number
• molarMass(formula: string, weights?: Record<string, number>): { counts, molarMass }
• ATOMIC_WEIGHTS – default weights map, override if you prefer specific standards.

CLI

npx chem-formula H_2O
# H_2O → 18.0153 g/mol
# Counts: { H: 2, O: 1 }

npx chem-formula "Fe_2(SO_4)_3" --json
# { "formula": "Fe_2(SO_4)_3", "counts": { ... }, "molarMass": 399.877 }

Dev

pnpm i
pnpm build
pnpm test

Notes

• Supports underscores for numeric subscripts: H_2, (SO_4)\_3.
• Also accepts bare digits after elements/groups for convenience: H2O.
• Handles nested (), [], {} and hydrate dots · or . (e.g., CuSO_4·5H_2O).
• For stricter underscore-only syntax, remove the bare-digit branch in lexer.ts.