pydantic/pydantic · error · ValueError

On field "{field_name}" the following field constraints are

Error message

On field "{field_name}" the following field constraints are set but not enforced: {", ".join(unused_constraints)}. 
For more details see https://docs.pydantic.dev/usage/schema/#unenforced-field-constraints

What it means

Raised as `ValueError` by `get_annotation_from_field_info` when constraints declared on a `Field(...)` are not actually applicable to the field's type. pydantic computes `constraints - used_constraints`; if anything is left over (e.g. `gt` on an `int` is fine, but `max_length` on an `int`, or `regex` on a number), it refuses to silently ignore them.

Source

Thrown at pydantic/v1/schema.py:1021

) -> Type[Any]:
    """
    Get an annotation with validation implemented for numbers and strings based on the field_info.
    :param annotation: an annotation from a field specification, as ``str``, ``ConstrainedStr``
    :param field_info: an instance of FieldInfo, possibly with declarations for validations and JSON Schema
    :param field_name: name of the field for use in error messages
    :param validate_assignment: default False, flag for BaseModel Config value of validate_assignment
    :return: the same ``annotation`` if unmodified or a new annotation with validation in place
    """
    constraints = field_info.get_constraints()
    used_constraints: Set[str] = set()
    if constraints:
        annotation, used_constraints = get_annotation_with_constraints(annotation, field_info)
    if validate_assignment:
        used_constraints.add('allow_mutation')

    unused_constraints = constraints - used_constraints
    if unused_constraints:
        raise ValueError(
            f'On field "{field_name}" the following field constraints are set but not enforced: '
            f'{", ".join(unused_constraints)}. '
            f'\nFor more details see https://docs.pydantic.dev/usage/schema/#unenforced-field-constraints'
        )

    return annotation


def get_annotation_with_constraints(annotation: Any, field_info: FieldInfo) -> Tuple[Type[Any], Set[str]]:  # noqa: C901
    """
    Get an annotation with used constraints implemented for numbers and strings based on the field_info.

    :param annotation: an annotation from a field specification, as ``str``, ``ConstrainedStr``
    :param field_info: an instance of FieldInfo, possibly with declarations for validations and JSON Schema
    :return: the same ``annotation`` if unmodified or a new annotation along with the used constraints.
    """
    used_constraints: Set[str] = set()

View on GitHub (pinned to 2e5f0e2b42)

Solutions

1. Remove or correct the constraint that does not apply to the annotated type (see the unused list in the message).
2. Move the validation into a @validator if you genuinely need it on that type.
3. Re-read the message: it names exactly which constraints are unenforced.

Example fix

// before
class M(BaseModel):
    age: int = Field(min_length=1)   # min_length is for strings

// after
class M(BaseModel):
    age: int = Field(ge=1)

# map of which constraints apply to which base type
_STR = {'min_length','max_length','regex'}
_NUM = {'gt','ge','lt','le','multiple_of'}
def constraints_match(type_, used) -> bool:
    import numbers
    return used <= (_STR if isinstance(type_, type) and issubclass(type_, str)
                   else _NUM if isinstance(type_, type) and issubclass(type_, numbers.Number) else set())

When it happens

Trigger: Declaring a Field with constraints that do not match the annotated type — e.g. `x: int = Field(min_length=4)`, `x: float = Field(regex='...')`, or `x: str = Field(gt=0)` (gt is numeric-only and unused on str). Also when applying a constraint that only exists for schema but not validation on an unsupported type.

Common situations: Copying a Field definition from another field of a different type, using a validator-style constraint on the wrong type, or assuming constraints are silently ignored if inapplicable.

Related errors

• Unable to apply constraint '{constraint}' to supplied value
• create-model-field-definitions
• invalid-annotated-type
• validate-by-alias-and-name-false
• The core schema type {choice["type"]!r} is not a valid discr

AI-assisted analysis of pydantic/pydantic@2e5f0e2b42 (2026-08-04). Data as JSON: /data/errors/31e357158b0792d2.json. Report an issue: GitHub.