JSON Schema generation from Pydantic models
Pydantic can generate a JSON Schema for any Pydantic schema, allowing self-documenting APIs and integration with tools that support JSON Schema format.
json_schema
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Pydantic JSON Schema compliance
Pydantic is compliant with the latest version of JSON Schema specification (2020-12), which is compatible with OpenAPI 3.1.
JSON Schema generation example
Example showing JSON Schema generation from a Pydantic model: from datetime import datetime from pydantic import BaseModel class Address(BaseModel): street: str city: str zipcode: str class Meeting(BaseModel): when: datetime where: Address why: str = 'No idea' print(Meeting.model_json_schema()) """ { '$defs': { 'Address': { 'properties': { 'street': {'title': 'Street', 'type': 'string'}, 'city': {'title': 'City', 'type': 'string'}, 'zipcode': {'title': 'Zipcode', 'type': 'string'}, }, 'required': ['street', 'city', 'zipcode'], 'title': 'Address', 'type': 'object', } }, 'properties': { 'when': {'format': 'date-time', 'title': 'When', 'type': 'string'}, 'where': {'$ref': '#/$defs/Address'}, 'why': {'default': 'No idea', 'title': 'Why', 'type': 'string'}, }, 'required': ['when', 'where'], 'title': 'Meeting', 'type': 'object', } """
json_schema_input_type argument for before/plain/wrap validators
When using before, plain, or wrap field validators, the accepted input type may differ from the field annotation. The json_schema_input_type argument can be provided to @field_validator to specify the correct input type in the JSON schema. If not provided, Pydantic uses the field type by default, except for plain validators where it defaults to Any since the field type is completely discarded.
json_schema_input_type example for before validator
Example of using json_schema_input_type: from typing import Any from pydantic import BaseModel, field_validator class Model(BaseModel): value: str @field_validator('value', mode='before', json_schema_input_type=int | str) @classmethod def cast_ints(cls, value: Any) -> Any: if isinstance(value, int): return str(value) else: return value Model.model_json_schema()['properties']['value'] produces {'anyOf': [{'type': 'integer'}, {'type': 'string'}], 'title': 'Value'}