Types and Validation

Flask-JSONRPC understands Python type hints and performs basic validation, ensuring that parameters match the expected types.

Supported Types

Out of the box, these types are validated:

  • int

  • float

  • str

  • bool

  • list and dict (validated recursively)

  • Optional[T]

  • typing.List[T]

  • typing.Dict[Key, Value]

Complex types (models, objects) require custom handling (see Patterns).

Return Type Validation

Return types are validated, too:

@jsonrpc.method("math.average")
def avg(nums: list[int]) -> float:
    return sum(nums) / len(nums)

If your method returns a value incompatible with the annotation, Flask-JSONRPC raises a JSON-RPC error.

Custom Validation with jsonschema

You may provide a JSON Schema manually:

@jsonrpc.method("user.create", schema={
    "type": "object",
    "properties": {
        "name": {"type": "string"},
        "age": {"type": "integer"},
    },
    "required": ["name"]
})
def create_user(name: str, age: int = None):
    ...

Using Pydantic (Optional Extension)

Pydantic models work well for strict typed JSON input:

from pydantic import BaseModel

class User(BaseModel):
    name: str
    age: int | None = None

@jsonrpc.method("user.create")
def create(user: User) -> dict:
    return user.dict()