Ensure consistent and safe handling of parameters and data across API endpoints. This includes using proper serialization methods, consistent parameter passing approaches, and context-aware processing when the same input may have different meanings. Key practices: - Use proper JSON serialization instead of string concatenation for API responses to prevent injection issues with user-provided data containing quotes or backslashes - Maintain consistent behavior patterns across related endpoints (e.g., if login stores origin URL in cookies, signup should follow the same pattern) - Pass parameters through appropriate channels - use hidden form fields instead of query parameters when dealing with sensitive or complex data - Design APIs to handle context-specific interpretations where the same parameter might reference different entities based on the calling context Example of proper JSON serialization: ```js // Instead of string concatenation: return JSON.stringify(this.name) + ":" + JSON.stringify(data); // Use proper object serialization: const object = { name: this.name, light: {...}, dark: {...} }; return JSON.stringify(object, null, 2); ``` This approach prevents security vulnerabilities, ensures predictable API behavior, and provides better developer experience through consistent interfaces.