Convert Joi Schemas to TypeScript interfaces

Usage no npm install needed!

<script type="module">
  import joiToTypescript from '';



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Convert Joi Schemas to TypeScript interfaces

Now supporting ESM and CJS Modules

This will allow you to use generate TypeScript interfaces from Joi Schemas that can be used to assign types to JavaScript objects or Hapi API requests. You no longer have to manually create the same structure again, saving you time and reducing errors.

For generating Open Api/Swagger this project works with

The use of .meta({className:'') is prefeerd over .label(''), because Joi.label() is intended to be used for meaningful error message, using it for another purpose makes Joi lose a standard feature, this is especially noticeable for frontend usages of Joi. The choice of the property className is because this property is used by joi-to-swagger making this project work with other projects.

Installation Notes

This package is intended as a development time tool, so it should be installed in the devDependencies

yarn add joi-to-typescript --dev
# or
npm install joi-to-typescript --save-dev

You will also need to install joi in the dependencies

yarn add joi
# or
npm install joi
  • This has been built for "joi": "^17" and will not work for older versions
  • Minimum node version 12 as Joi requires node 12

Suggested Usage

  1. Create a Schemas Folder eg. src/schemas
  2. Create a interfaces Folder eg. src/interfaces
  3. Create Joi Schemas in the Schemas folder with a file name suffix of Schemas eg. AddressSchema.ts
    • The file name suffix ensures that type file and schema file imports are not confusing


Example Project

Explore the Example Projects for recommended setup, execute yarn types to run each one.

Example Schema

This example can be found in src/__tests__/readme

import Joi from 'joi';

// Input
export const JobSchema = Joi.object({
  businessName: Joi.string().required(),
  jobTitle: Joi.string().required()
}).meta({ className: 'Job' });

export const WalletSchema = Joi.object({
  usd: Joi.number().required(),
  eur: Joi.number().required()
  .meta({ className: 'Wallet', unknownType: 'number' });

export const PersonSchema = Joi.object({
  firstName: Joi.string().required(),
  lastName: Joi.string().required().description('Last Name'),
  job: JobSchema,
  wallet: WalletSchema
}).meta({ className: 'Person' });

export const PeopleSchema = Joi.array()
  .meta({ className: 'People' })
  .description('A list of People');

// Output
 * This file was automatically generated by joi-to-typescript
 * Do not modify this file manually

export interface Job {
  businessName: string;
  jobTitle: string;

 * A list of People
export type People = Person[];

export interface Person {
  firstName: string;
  job?: Job;
   * Last Name
  lastName: string;
  wallet?: Wallet;

export interface Wallet {
   * Number Property
  [x: string]: number;
  eur: number;
  usd: number;
Points of Interest
  • export const PersonSchema schema must be exported
  • export const PersonSchema includes a suffix of Schema so the schema and interface are not confused when using import statements (recommended not required)
  • .meta({ className: 'Person' }); Sets interface name using TypeScript conventions (TitleCase Interface name, camelCase property name)
  • .meta({ unknownType: 'number' }); assert unknown type to number

Upgrade Notice

  • Version 1 used .label('Person') as the way to define the interface name, to use this option set { useLabelAsInterfaceName: true }

Example Call

import { convertFromDirectory } from 'joi-to-typescript';

  schemaDirectory: './src/schemas',
  typeOutputDirectory: './src/interfaces',
  debug: true

// or to get an interface as a string. Please note that this method is limited
import { convertSchema } from 'joi-to-typescript';
const resultingInterface = convertSchema({}, JobSchema);
resultingInterface?.content = // the interface as a string


export interface Settings {
   * The input/schema directory
   * Directory must exist
  schemaDirectory: string;
   * The output/type directory
   * Will also attempt to create this directory
  typeOutputDirectory: string;
   * Use .label('InterfaceName') instead of .meta({className:'InterfaceName'}) for interface names
  useLabelAsInterfaceName: boolean;
   * Should interface properties be defaulted to optional or required
   * @default false
  defaultToRequired: boolean;
   * What schema file name suffix will be removed when creating the interface file name
   * @default "Schema"
   * This ensures that an interface and Schema with the file name are not confused
  schemaFileSuffix: string;
   * If `true` the console will include more information
   * @default false
  debug: boolean;
   * File Header content for generated files
  fileHeader: string;
   * If true will sort properties on interface by name
   * @default true
  sortPropertiesByName: boolean;
   * If true will not output to subDirectories in output/interface directory. It will flatten the structure.
  flattenTree: boolean;
   * If true will only read the files in the root directory of the input/schema directory. Will not parse through sub-directories.
  rootDirectoryOnly: boolean;
   * If true will write all exports *'s to root index.ts in output/interface directory.
  indexAllToRoot: boolean;
   * Comment every interface and property even with just a duplicate of the interface and property name
   * @default false
  commentEverything: boolean;
   * List of files or folders that should be ignored from conversion. These can either be
   * filenames (AddressSchema.ts) or filepaths postfixed with a / (addressSchemas/)
   * @default []
  ignoreFiles: string[];
   * The indentation characters
   * @default '  ' (two spaces)
  indentationChacters: string;

Joi Features Supported

  • .meta({className:'InterfaceName'}) - interface Name and in jsDoc
  • .description('What this interface is for') - jsdoc
  • .valid(['red', 'green', 'blue']) - enumerations
  • .optional() - optional properties ?
  • .required() - required properties
  • .array(), .object(), .string(), .number(), .boolean() - standard Joi schemas
  • .alternatives()
  • .allow('') - will be ignored on a string
  • .allow(null) - will add as an optional type eg string | null
  • .unknown(true) - will add a property [x: string]: unknown; to the interface
    • Assert unknown to some type with a stringified type or a Joi schema, e.g.:
      .meta({ unknownType: 'some-type' })
      .meta({ unknownType: Joi.object({ id: Joi.string() }) })`
  • .example() - jsdoc
  • .cast() - currently will honor casting to string and number types, map and set to be added later
  • And many others


Recommended Development Environment

Recommended Editor is VS Code, this project is setup with VSCode settings in the ./.vscode directory to keep development consistent.

Best developed on macOS, Linux, or on Windows via WSL. Node 12, 14, or 16

Install nodejs via nvm so you can have multiple versions installed

nvm use # using NVM to select node version
yarn install # using yarn
yarn test # run local tests

yarn coverage # test coverage report
yarn lint # lint the code

Change Log

See GitHub Releases