rut.ts

A tiny, zero-dependency TypeScript toolkit for validating, formatting, cleaning, and generating Chilean RUT/RUN values — built and hardened for production identity flows.

Version 4.0.0 is a major, breaking release. It adds production identity hardening: bounded (ReDoS-safe) input parsing, strict format validation, verifier checking inside format(), generic error messages, and a crypto-backed generate(). Coming from 3.x? Read the migration guide before upgrading.

Why rut.ts#

A regular expression can tell you a string looks like a RUT. It cannot tell you the verifier digit is correct, and a careless one is easy to make vulnerable to catastrophic backtracking. rut.ts does the real work:

Correct, not just plausible

Validates the actual Modulo 11 check digit — the difference between “looks like a RUT” and “is a valid RUT”.

Hardened for identity flows

Bounds input length before parsing, rejects non-canonical and placeholder values in strict mode, and never echoes ID values into errors or logs.

Runs everywhere

Zero runtime dependencies. ESM + CJS, fully tree-shakeable, identical on Node, Deno, Bun, the Edge, and the browser.

Fully typed

Comprehensive TypeScript definitions across the entire API surface, with safe (non-throwing) modes built in.

Try it now#

This runs the same Modulo 11 algorithm rut.ts ships. Type any RUT and watch every function respond live:

Try it — type any RUT

isRutLike()true

validate()true

validate({ strict: true })true

clean()123456785

format()12.345.678-5

decompose().body12345678

decompose().verifier5

calculateVerifier(body)5

verifier if input is a bodynot applicable

What is a RUT?#

The RUT (Rol Único Tributario) is Chile's unique identification number, used for taxes, legal identification, government services, and banking. For natural persons it is also called a RUN (Rol Único Nacional) — same structure, same check digit, so every function here works identically for both.

It is written as XX.XXX.XXX-Y:

X — body, 7–8 digits
Y — verifier digit, 0–9 or K

Example: 12.345.678-5

The verifier is derived from the body with the Modulo 11 algorithm, which is what lets a RUT be checked for authenticity without contacting any registry.

Quick example#

TypeScript

import { validate, format, clean } from 'rut.ts'
 
validate('12.345.678-5')              // true
validate('12.345.678-0')              // false (wrong verifier)
 
format('123456785')                   // '12.345.678-5'
clean('12.345.678-5')                 // '123456785'
 
clean('invalid', { throwOnError: false }) // null (safe mode)

Where to next#

Installation

Install with npm, pnpm, bun, or yarn — and verify your setup.

Quick Start

Validate, format, and store a RUT end to end in five minutes.

Features

The nine focused functions and how they compose.

API Reference

Signatures, options, and types for the whole surface.

Security

The hardening model behind v4 and how to use it safely.

Examples

Forms, React, Zod, error handling, and real-world patterns.

License#

MIT © Arrow Software. Free for personal and commercial use, including closed-source and paid products — no usage limit, no attribution required beyond keeping the license notice.

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