@jetio/schema-builder

A fluent, type-safe API for constructing JSON Schemas programmatically. Build complex schemas with autocomplete, validation, and zero boilerplate — and get automatic TypeScript type inference from the same build() call.

Three things from one schema

Write a schema once and build() gives you a fluent builder, a matching TypeScript type via Jet.Infer<>, and runtime validation — all enforcing the same rules, none of them able to drift apart.

import { SchemaBuilder, Jet, JetValidator } from "@jetio/schema-builder";
 
const userSchema = new SchemaBuilder()
  .object()
  .properties({
    id: (s) => s.number(),
    name: (s) => s.string(),
    email: (s) => s.string().format("email"),
  })
  .required(["id", "name", "email"])
  .build();
 
type User = Jet.Infer<typeof userSchema>;
// { id: number; name: string; email: string }
 
const validate = new JetValidator().compile(userSchema);
validate({ id: 1, name: "Alice", email: "alice@example.com" }); // true

Why it’s different

• Spec-compliant inference — types behave like JSON Schema, not just resemble it. If the validator rejects it, TypeScript rejects it too.
• oneOf is actually exclusive — the other branch’s keys are marked never automatically, giving a true discriminated union with no kind tag required.
• if / then / elseIf / else are inferred — conditional types from conditional schemas, including elseIf, which no other TypeScript schema library supports.
• Full draft coverage — Draft 06 through 2020-12, including unevaluatedProperties, prefixItems, $dynamicRef, and patternProperties mapped to template-literal keys.
• No as const — literal types from .enum() and .const() are inferred for you.

Try it live

No install required — open the playground on StackBlitz → 

Where to go next