Detecting Implicit Type Coercion Drift in Pydantic Models Using Strict Validation

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A developer describes prototyping a static validation tool that flags implicit type casting in Pydantic models, aimed at FastAPI-style web APIs. The approach validates input in strict mode and then in normal mode, reporting fields where coercion silently occurs. The prototype hit design problems, including failures when a required sample file was missing and CI non-determinism from auto-generated test data. Locating errors in deeply nested structures via the ValidationError location path also proved unreliable and hurt report clarity. The project was not judged production-ready, but the author offers lessons on separating coercion checks from business validation and supplying schema files during CI setup.

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