Strict Pydantic v2 Validation Guards FastAPI APIs Against Silent Type Coercion

An engineering article examines how default lax validation in FastAPI and Pydantic v2 can silently convert values such as strings to integers, hiding schema drift between clients and servers. It proposes enforcing strict mode with forbidden extra fields, paired with orjson for fast byte-level deserialization. The author describes a validation pipeline that rejects mismatched payloads and undeclared attributes, and includes a dependency guard that installs missing packages via parameterized subprocess calls. The piece also reports on a post-mortem of an encoding failure found during pipeline testing, showing how transport-layer issues can compromise payload integrity.