voluptuous

Schemas use native Python data structures like dictionaries and lists, making them easy to read and write without learning a new DSL or subclassing.

Validators are plain Python callables, allowing custom validation logic with simple functions, as shown in examples using datetime or custom checks.

Raises Invalid exceptions with descriptive messages and paths (e.g., @ data['key']), helping pinpoint validation failures in complex data structures.

Handles nested dictionaries, lists, and recursive schemas with Self, providing consistency across simple and complex validation scenarios.