when schema is: {type: "object", default: "foo"}, the result type is: type Schema = string;

[inceptiongt]

when "type" value is mismatch "defualt" value's type, the resutl is wrong.

This: { "type": "object", "default": "foo" }

Results in: export type Schema = string;

While I would have expected: export interface Schema { propertiesA: ... propertiesB: ... }

Without "default" or "default": {} it works fine.

[bcherny]

What does it mean for default to be a string, while the type of the schema is an object?

JSON-Schemas accept the combination of the different types they may be; in your case, because default is a string, that tells JSTT that the schema could be a string; JSTT then ignores type (which is a bug). The right behavior is to accept either an object or a string. Would you prefer the following type?:

interface Schema1 {
  [k: string]: unknown
}

export type Schema = Schema1 | string