import { validate, format, clean } from 'rut.ts'
import { isValidRut, type Rut } from 'rut.ts'
validate('12.345.678-5') // → true
format('123456785') // → '12.345.678-5'
clean('12.345.678-5') // → '123456785'
validate('11.111.111-1', { strict: true }) // → false
if (isValidRut(input)) save(input) // input: Rut ✓Rut.ts provides a comprehensive and battle tested set of functions for working with Chilean RUT values.
From verifier-digit math to live input formatting — each function does one job well, so you compose only what you need.
By example
Twelve composable functions across real scenarios — a branded Rut type, live-input formatting, masking, PII-safe errors, and crypto-backed generation. Tab through to see them in context.
import { validate, format, clean } from 'rut.ts'
validate('12.345.678-5') // → true
format('123456785') // → '12.345.678-5'
format('123456785', { dots: false }) // → '12345678-5'
clean('12.345.678-5') // → '123456785'Live demo
Every value below is computed live by rut.ts running in your browser. No server, no mocks — the exact functions you'd call in your own app.
Why a library
Most options — and a regex plus a Modulo 11 check — will validate a well-formed RUT. The difference is everything around it: strict and ReDoS-safe input handling, a branded Rut type that flows through your code, PII-safe typed errors, masking, generation, and the breadth to compose anything. Here's how the alternatives compare.
| Capability | Other libraries | Manual regex + Modulo 11 | rut.ts |
|---|---|---|---|
| Matches the RUT shape | Supported | Supported | Supported |
| Verifies the Modulo 11 check digit | Supported | Supported | Supported |
| Strict mode — rejects placeholders & non-canonical input | Partial support | Not supported | Supported |
| Bounded input length — ReDoS-safe | Partial support | Partial support | Supported |
| Branded Rut type + type guard (isValidRut) | Not supported | Not supported | Supported |
| Non-throwing safe mode (throwOnError: false) | Partial support | Not supported | Supported |
| Incremental formatting for live inputs | Not supported | Not supported | Supported |
| RUT masking for safe logging (mask) | Not supported | Not supported | Supported |
| Typed, PII-safe errors (InvalidRutError) | Not supported | Not supported | Supported |
| Crypto-backed valid RUT generation | Partial support | Not supported | Supported |
| Decomposition & value-based comparison (decompose, equals) | Partial support | Not supported | Supported |
| Actively maintained & tested (523 cases) | Partial support | Not supported | Supported |
rut.ts is the focused, hardened, fully-typed version of all this — twelve composable functions with safe and strict modes, a branded Rut type, and PII-safe errors, in ~1.62 KB and actively maintained.
Zero dependencies and pure TypeScript. Rut.ts behaves identically on Node, Deno, and Bun, at the Edge and on Vercel Functions, and inside any frontend framework — React, Next.js, Astro, or vanilla in the browser.
Add the package with your manager of choice: npm install rut.ts — also works with bun, pnpm, and yarn.
Pull in only what you need: import { validate, format } from 'rut.ts'. Fully typed and tree-shakeable.
Call validate('12.345.678-5') to check a RUT, or format('123456785') to clean it up. Strict and safe (non-throwing) modes included.
Zero dependencies, zero config. The same code runs on Node, Deno, Bun, the Edge, and the browser.
The RUT (Rol Único Tributario) is Chile's unique identification number, used for tax purposes, legal identification, government services, and banking. It's written as XX.XXX.XXX-Y — a 7–8 digit body followed by a single verifier digit (0–9 or K). For example: 12.345.678-5.
That final character is a check digit derived from the body using the Modulo 11 algorithm, which is what lets a RUT be validated for authenticity without contacting any registry. Computing and verifying it correctly is exactly what rut.ts handles for you.
The blog covers the engineering behind rut.ts — how validation, formatting, and manipulation actually work, and the trade-offs behind the API.
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