VALIDATIONERROR

ValidationError is a type of error or exception that signals a failure of data to meet defined validation rules within a software system. It indicates that the provided input cannot be accepted without modification because it violates constraints such as type, format, range, or required fields.

The error is used across different layers, including user input forms, API request handling, configuration loading, and data deserialization. Validation can occur synchronously or asynchronously, and a ValidationError typically contains information about what failed and where the failure occurred, helping developers and clients understand how to correct the data.

In many frameworks, a ValidationError includes a message and a collection of field- or attribute-specific errors. For example, Django’s ValidationError can be tied to particular model fields; Pydantic’s ValidationError provides details for each field with a path, type, and message; and Marshmallow’s ValidationError carries per-field errors. The structured nature of these errors supports precise feedback and automated remediation.

Handling strategies usually involve returning a client-appropriate error response, commonly 400 Bad Request or 422 Unprocessable Entity, along with clear, actionable messages. Best practices emphasize avoiding leakage of sensitive information, providing structured error details suitable for programmatic consumption, and guiding users toward correct input formats and constraints. ValidationError thus plays a central role in ensuring data integrity and robust user interactions.