Defense In Depth Validation

Defense-in-Depth Validation Skill

Validate at every layer data passes through to make bugs structurally impossible.

Overview

This skill teaches adding validation at multiple system layers instead of a single checkpoint. By validating at entry points, business logic, environment guards, and with debug instrumentation, bugs become impossible to reproduce rather than just "fixed."

The Four Layers

1. Entry Point Validation - Reject obviously invalid input at API boundary
2. Business Logic Validation - Ensure data makes sense for operations
3. Environment Guards - Prevent dangerous operations in specific contexts
4. Debug Instrumentation - Capture context for forensics

When to Use

• Invalid data causes failures deep in execution
• Bug fix required at multiple system layers
• Single validation point proves insufficient
• Need to make bugs structurally impossible
• Refactoring code paths that bypass existing checks

Key Insight

Single validation: "We fixed the bug" Multiple layers: "We made the bug impossible"

Different layers catch different cases - entry validation catches most bugs, business logic catches edge cases, environment guards prevent context-specific dangers.

Auto-Trigger Keywords

• data validation
• input sanitization
• defense in depth
• bug prevention
• layer validation
• structural bugs
• validation patterns
• security boundaries

Source

Adapted from mrgoonie/claudekit-skills