Generated OpenAPI schemas use "nullable" instead of ["type","null"] #5432
Description
When generating JSON Schema for OpenAI, the current z.toJSONSchema(..., { target: 'openapi-3.0' }) output produces invalid structures that are not accepted by the OpenAI API.
According to the OpenAI documentation:
All fields in properties must be marked as required.
You can denote optional fields by adding null as a type option (see example below).
— OpenAI Function Calling · Strict Mode
However, toJSONSchema still emits nullable: true, which is not valid in the JSON Schema format OpenAI expects.
Example:
import z from 'zod';
const Schema = z.object({
option1: z.union([z.string(), z.null()]),
option2: z.string().nullable(),
option3: z.nullable(z.string()),
});
const schema = z.toJSONSchema(Schema, {
target: 'openapi-3.0',
});
console.log(schema);Output:
{
"additionalProperties": false,
"properties": {
"option1": {
"anyOf": [
{
"enum": [
null
],
"nullable": true,
"type": "string"
},
{
"type": "string"
}
]
},
"option2": {
"nullable": true,
"type": "string"
},
"option3": {
"nullable": true,
"type": "string"
}
},
"required": [
"option1",
"option2",
"option3"
],
"type": "object"
}Expected:
{
"additionalProperties": false,
"properties": {
"option1": {
"type": [
"null",
"string"
]
},
"option2": {
"type": [
"null",
"string"
]
},
"option3": {
"type": [
"null",
"string"
]
}
},
"required": [
"option1",
"option2",
"option3"
],
"type": "object"
}