marshmallow-jsonschema: JSON Schema Generation from Marshmallow Schemas

0.13.0 · maintenance · verified Sun Apr 12

marshmallow-jsonschema translates marshmallow schemas into JSON Schema Draft v7 compliant jsonschema. It enables developers to generate JSON Schemas directly from their existing Marshmallow schemas, which is particularly useful for frontend form generation, API documentation, or validation in other systems. The current version is 0.13.0, released in October 2021, suggesting a maintenance rather than a rapid release cadence.

Warnings

breaking `marshmallow-jsonschema` is not compatible with `marshmallow.fields.Enum` introduced in Marshmallow v3.18.0. Using this field type will result in an `UnsupportedValueError`.
Fix: Avoid using `marshmallow.fields.Enum` or consider using the `marshmallow-jsonschema-3` fork which addresses this and other OpenAPI/JSON Schema 3.x features. Alternatively, implement custom field handling for enums.
deprecated When used with newer Marshmallow versions (e.g., v4.x), `marshmallow-jsonschema` may produce `RemovedInMarshmallow4Warning` warnings related to deprecated field attributes like `default` (use `dump_default`) and passing field `metadata` as keyword arguments (use explicit `metadata=` argument).
Fix: These are warnings from Marshmallow itself, not `marshmallow-jsonschema`. While the library might still function, upgrading `marshmallow-jsonschema` to a version that properly supports Marshmallow 4.x is the long-term solution. For now, ensure your Marshmallow schemas follow the latest best practices for field definition.
gotcha `marshmallow-jsonschema` only supports converting Marshmallow schemas *to* JSON Schema. There is no built-in functionality to generate a Marshmallow schema *from* an existing JSON Schema.
Fix: If you need to generate Marshmallow schemas from JSON Schema, you will need to use a different tool or implement a custom solution. This library is strictly a one-way conversion tool.

Install

pip install marshmallow-jsonschema Install stable version

Imports

JSONSchema

from marshmallow_jsonschema import JSONSchema

Quickstart

This quickstart demonstrates how to define a basic Marshmallow schema and then use `marshmallow-jsonschema` to convert it into a JSON Schema representation. The output is a standard JSON Schema dictionary, ready for use in other applications.

from marshmallow import Schema, fields
from marshmallow_jsonschema import JSONSchema

class UserSchema(Schema):
    username = fields.String(required=True, metadata={'description': 'The user\'s unique identifier'})
    age = fields.Integer(required=False, allow_none=True, metadata={'minimum': 0})
    email = fields.Email(required=True)

# Instantiate the JSONSchema converter
json_schema_converter = JSONSchema()

# Convert your Marshmallow schema to a JSON Schema dictionary
user_json_schema = json_schema_converter.dump(UserSchema())

import json
print(json.dumps(user_json_schema, indent=2))

view raw JSON →