Typescript -> JSON Schema Output contains "type": "{string}" instead of "type": "string"

[vamsiampolu]

I am trying to convert a type that looks like:

import type {Person} from '@myorg/common-types"

export type MemberInfo = Required<Person>;

where person is defined in a common library:

export type Person = {
/**
*
* @type {string}
* @memberof {Person}
*/
name: string;
}

The output type looks something like:

```json
{
  "type": "object",
   "properties": {
      "name": "{string}"
   }
}

I used the following in an npm script:

{
  "scripts": {
     "generate:schema":"quicktype --src ./types/post/memberInfoTypes.ts --src-lang typescript --lang schema --out ./schemas/post/memberInfoSchema.json"    
  }
}

Issue Type

Quicktype Output (JSON Schema from Typescript)

Context (Environment, Version, Language)

Nodejs Version: v20.19.0
Package Manager: pnpm 10.6.2
OS: MacOS 15.4

Input Format: Typescript
Output Language: JSON Schema

CLI
Version: 23.0.171

Description

I would like to take existing typescript types and convert them to json schema for validation using something like ajv.

Input Data

export type MemberInfo = Required<Person>;

where person is defined in a common library:

export type Person = {
  /**
     *
     * @type {string}
     * @memberOf {Person}
   */
  name: string;
}

Expected Behaviour / Output

The type string is valid JSON Schema while the type "{string}" is not.

{
  "type": "object",
   "properties": {
      "name": "string"
   }
}

Current Behaviour / Output

{
  "type": "object",
   "properties": {
      "name": "{string}"
   }
}

My wild guess is that it may be reading the JSDoc annotations and using them to infer types instead of relying on the typescript definition.

Steps to Reproduce

Clone the repo: https://github.com/vamsiampolu/quicktype-ts-to-json-schema-issue

1. Run nvm use to set the Node version
2. Run pnpm install to install the dependencies.
3. Run the script pnpm generate:schema from the repository

Possible Solution

[schani]

Triage note (systematic backlog sweep, assisted by Claude): confirmed reproducible on current master (v23.3.0, 68ecb284).

Root cause

The forked @mark.probst/typescript-json-schema (used by packages/quicktype-typescript-input) lists "type" among its honored validationKeywords, so a JSDoc @type {string} tag gets copied verbatim — braces included — into definition.type. TypeScript-to-schema output then emits the invalid "type": "{string}", and feeding that same schema (or any schema with a JSDoc-derived brace-wrapped type) to any other target language fails hard with Invalid type {string} in JSON Schema (see packages/quicktype-core/src/input/JSONSchemaInput.ts).

@type JSDoc annotations of this style are common output from tools like openapi-generator, so this isn't a contrived edge case.

Assessment

• Severity: medium — produces invalid JSON Schema from valid TS input, and cascades into a hard failure for every other output language once that schema is reused.
• Difficulty: moderate — the correct fix (strip braces from / ignore the JSDoc type tag) lives in the forked typescript-json-schema and needs a fork release; a sanitizing post-pass in packages/quicktype-typescript-input/src/index.ts would be a faster workaround.

Reproduction

node dist/index.js --src person.ts --src-lang typescript --lang schema

person.ts:

export type Person = {
  /**
     *
     * @type {string}
     * @memberOf {Person}
   */
  name: string;
}

export type MemberInfo = Required<Person>;

Output includes "type": "{string}" for the name property. Feeding a minimal schema with that same invalid type to another language (e.g. --lang go) then fails with:

Error: Invalid type {string} in JSON Schema at bad.schema.json#/properties/name.