@papack/schema

Opinionated, fully synchronous TypeScript schemas for developers who want strict, minimal, predictable data structures.
No nulls. No undefined. No async. No partial optionality.

Core Rules

• Sync only — no Promises anywhere.
• First error wins — validate() throws immediately.
• Objects are all-required or all-optional — never mixed.
• No null/undefined —
  • values: "" or 0
  • lists: []
• Only validate() — no parse, no safeParse.
• Strong typing — Infer<T> extracts exact static types.
• Describe — inspect schema for UI forms, etc.
• Checks — curried, functional; includes char(n), isPassword, isIban, etc.
• Union checks — support primitive unions, never object unions.

Installation

npm install @papack/schema

Concept

With the three primitives — object, list, value — you can express any structure. Strict, lightweight, zero magic.

Examples

Basic schema

import { object, value, isString } from "@papack/schema";

const UserSchema = object({
  name: value(isString),
});

UserSchema.validate({ name: "Max" });

Complete example

import {
  value,
  object,
  partial,
  pick,
  omit,
  Infer,
  isUnionList,
  isPassword,
  isString,
  extend,
  isBoolean,
} from "@papack/schema";

const UserSchema = object({
  name: value(isString)

  pw: value(
    isPassword({
      minLength: 8,
      minNumbers: 1,
      minSpecialChars: 1,
    })
  ),

  gender: value(isUnionList(["w", "m"], { allowEmpty: true })),
});

// Derived schemas
const a = pick(UserSchema, ["name"]);
const b = omit(UserSchema, ["name"]);
const c = partial(UserSchema);

// Extended schema
const d = extend(UserSchema, {
  locked: value(isBoolean),
});

// Final schema
const e = omit(d, ["name"]);
type User = Infer<typeof e>;

const u: User = {
  gender: ["m", "m"],
  locked: false,
  pw: "asdfias2df!sadfed",
};

d.validate(u);

Using describe()

const info = UserSchema.describe();
// Structural metadata for:
// - UI form builders
// - tools, automation, codegen

Errors

Errors are short, stable, and i18n-ready. Examples:

• "TOO_SMALL"
• "NOT_STRING"
• "INVALID_UNION"

validate() throws always on the first error.

Design Intent

• Minimal surface, predictable behavior.
• No hidden transformations.
• No optional-field chaos.