@overtimepog

Implement comprehensive input validation on server-side with complementary client-side validation for user experience, using allowlists, type checking, and sanitization to prevent injection attacks. Use this skill when validating user inputs, form data, API requests, file uploads, query parameters, or any external data entering the application. Apply this skill when implementing server-side validation as the primary security layer, adding client-side validation for immediate user feedback, validating data types and formats, checking ranges and required fields, sanitizing inputs to prevent SQL injection and XSS attacks, using allowlists over blocklists, providing field-specific error messages, or enforcing business rules at appropriate application layers. This skill ensures validation happens at all entry points consistently, security is never dependent on client-side checks alone, users receive helpful immediate feedback, and data integrity is maintained through multiple layers of validation.