https://github.com/nvie/decoders

Elegant validation library for type-safe input data for TypeScript
https://github.com/nvie/decoders

checking composition decoders elm flow input javascript type typescript validation

Last synced: 26 days ago
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Elegant validation library for type-safe input data for TypeScript

• Host: GitHub
• URL: https://github.com/nvie/decoders
• Owner: nvie
• License: mit
• Created: 2017-10-04T19:40:11.000Z (over 8 years ago)
• Default Branch: main
• Last Pushed: 2026-03-01T21:41:16.000Z (about 1 month ago)
• Last Synced: 2026-03-01T21:48:34.650Z (about 1 month ago)
• Topics: checking, composition, decoders, elm, flow, input, javascript, type, typescript, validation
• Language: TypeScript
• Homepage: https://decoders.cc
• Size: 46.2 MB
• Stars: 395
• Watchers: 4
• Forks: 28
• Open Issues: 5
• Metadata Files:
  • Readme: README.md
  • Changelog: CHANGELOG.md
  • Funding: .github/FUNDING.yml
  • License: LICENSE

Awesome Lists containing this project

• awesome-flow - decoders - Type-safe data validation for Flow. (Packages / Helpers)
• awesome-list - decoders - safe input data (for TypeScript and Flow) | nvie | 262 | (JavaScript)

README

          



[![npm](https://img.shields.io/npm/v/decoders.svg)](https://www.npmjs.com/package/decoders)

[![Test Status](https://github.com/nvie/decoders/actions/workflows/test.yml/badge.svg?branch=main)](https://github.com/nvie/decoders/actions)

[![Bundle size for decoders](https://pkg-size.dev/badge/bundle/4200)](https://pkg-size.dev/decoders)

Elegant and battle-tested validation library for type-safe input data for TypeScript.

## Basic example

```typescript

import { array, isoDate, number, object, optional, string } from 'decoders';

// Incoming data at runtime, e.g. the request body

// The point is that this data is untrusted and its type unknown

const externalData = {

  id: 123,

  name: 'Alison Roberts',

  createdAt: '2026-01-11T12:26:37.024Z',

  tags: ['foo', 'bar'],

};

// Write the decoder (= what you expect the data to look like)

const userDecoder = object({

  id: number,

  name: string,

  createdAt: optional(isoDate),

  tags: array(string),

});

// Call .verify() on the incoming data

const user = userDecoder.verify(externalData);

//    ^^^^

//    TypeScript will infer this type as:

//    {

//      id: number;

//      name: string;

//      createdAt?: Date;

//      tags: string[];

//    }

```

## Installation

```bash

npm install decoders

```

## Requirements

You must set `strict: true` in your `tsconfig.json` in order for type inference to work

correctly!

```js

// tsconfig.json

{

  "compilerOptions": {

    "strict": true

  }

}

```

## Documentation

Documentation can be found on [decoders.cc](https://decoders.cc).

There is a dedicated page that explains how to

[build your own decoders](https://decoders.cc/docs/building-your-own).