Data Validation Schema-based data validation across languages and formats. Covers JSON Schema, Zod (TypeScript), Pydantic (Python), API boundary validation, data contracts, and integrity checking. When to Use - Defining the shape of API request/response bodies - Validating user input before processing - Setting up data contracts between services - Checking CSV/JSON file integrity before import - Migrating data (did the ETL preserve everything?) - Generating types or documentation from schemas JSON Schema Basic schema Common patterns Validate with command line Zod (TypeScript) Basic schemas Ad…