Every Readability Formula Explained (with JavaScript Examples)

Readability formulas have been around since the 1940s. The U.S. military commissioned the first one to make training manuals less confusing. Newspapers adopted them to keep articles accessible. Today, content teams at organizations like gov.uk and the NYT use them to measure whether their writing actually reaches people. But if you search for "readability formulas javascript," you get scattered npm packages — each implementing one formula — and blog posts from 2018. No single guide covers all the formulas with working code you can install and run. This article covers all 8 major readability formulas, explains the math behind each one, and shows how to compute them in JavaScript with textlens . Setup npm install textlens textlens is a zero-dependency TypeScript toolkit. It works in Node.js 16+ and ships ESM and CommonJS with full type definitions. const { readability , statistics } = require ( ' textlens ' ); // or: import { readability, statistics } from 'textlens'; Every example below