LOOM Schema

A schema system that does exactly what you need.
Type inference. Runtime validation. JSON Schema generation.
Zero build steps. No extra fluff. It just works.

Read the docs

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LOOM Schema was built because nothing else got this balance right:

• ✅ Type-safe and composable
• ✅ Validates at runtime
• ✅ Emits spec-compliant JSON Schema
• ❌ No codegen
• ❌ No decorators
• ❌ No build step

You write schema-like TypeScript. You get real JSON Schema and real validation. That’s the whole point.

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Install

bun add loom-schema

Everything’s bundled — including ajv and ajv-formats. No extra dependencies.

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Example

import { object, string, number, Infer } from "loom-schema";

const User = object({
  name: string({ minLength: 1 }),
  age: number({ minimum: 0 }),
});

type UserType = Infer<typeof User>;

const result = await User.validate({ name: "Ada", age: 32 });

if (!result.valid) {
  console.error(result.errors);
}

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Use Cases

Use LOOM Schema when you need to feed schemas into systems that expect schemas:

• OpenAI Function calling
• MCP & function serialization
• API endpoints with runtime enforcement
• Config validation and generation
• Frontend forms based on types
• CLI arg structure and validation

If it wants a schema, LOOM can give it one — safely, programmatically, and without ceremony.

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Features

• 📐 TypeScript-first: deeply inferred types
• 🧩 Composable fragments: mix and reuse schema pieces with ease
• 🎛 All the basics: allOf, anyOf, oneOf, conditionals, etc.
• 📄 Standards-based: JSON Schema 2020-12 compliance
• 🧪 Runtime validation: powered by AJV with formats out of the box
• 📦 No config, no build step, no codegen

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Schema Inference

const Config = object({
  apiKey: string(),
  retries: number({ default: 3 }),
});

type ConfigType = Infer<typeof Config>;
// {
//   apiKey: string;
//   retries: number;
// }

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Composition

import { allOf, object, string } from "loom-schema";

const WithId = object({ id: string({ format: "uuid" }) });

const Product = allOf([
  WithId,
  object({
    name: string(),
    description: string(),
  }),
]);

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Validation

const result = await Product.validate({
  id: "123e4567-e89b-12d3-a456-426614174000",
  name: "Widget",
  description: "An example widget",
});

Returns { valid, errors } from AJV — clean and informative.

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Philosophy

LOOM Schema wasn’t built to be trendy. It was built to be minimal, practical, and actually usable across systems that expect real JSON Schema. It gives you the right pieces to build and validate data shapes at runtime — without taking over your project.

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You write types.
You get schemas.
That’s it.