Building a Type-Safe CLI with @fotros/cli and @fotros/schema

Modern CLIs do a lot more than just run commands. They read config files, validate user input, and provide rich error messages. This tutorial builds a full CLI from scratch using @fotros/cli for the command layer and @fotros/schema for config validation.

Project Setup

mkdir my-cli && cd my-cli

npm init -y

npm install @fotros/cli @fotros/schema

npm install -D typescript @types/node

Defining the Config Schema

Before writing any command logic, define the shape of your config file. This schema becomes your single source of truth for both validation and TypeScript types.

import { createParser } from '@fotros/schema';

export const ConfigSchema = createParser({

  apiUrl: String,

  token: String,

  timeout: Number.optional().default(5000),

  debug: Boolean.optional().default(false),

});

export type Config = typeof ConfigSchema._output;