How does this skill improve system security?

By validating data at every boundary, it prevents injection attacks and unauthorized state changes that often occur when internal layers trust inputs implicitly.

What is the main benefit of defense-in-depth validation?

It makes bugs structurally impossible by ensuring that even if one validation layer is bypassed by a refactor or a mock, other layers will catch the error.

When should I apply this pattern?

Apply this pattern when invalid data causes failures deep in execution or when performing high-risk operations like file system changes or database writes.

What are the four layers of validation recommended?

The strategy uses Entry Point Validation, Business Logic Validation, Environment Guards, and Debug Instrumentation to provide total coverage.

Does this replace standard unit testing?

No, it complements testing by adding runtime guards. While tests prove code works today, defense-in-depth ensures it stays safe even as the codebase evolves.

Defense-in-Depth Validation

Name: Defense-in-Depth Validation
Author: NickCrew

byNickCrew

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Security & Testing

Implements multi-layered data validation patterns to prevent bugs and failures from propagating through system boundaries.

About

The Defense-in-Depth skill empowers Claude to adopt a proactive security and stability posture by enforcing validation at every architectural boundary. Instead of relying on a single check that can be bypassed by refactoring or mocks, this skill guides the implementation of four distinct layers: entry point validation, business logic verification, environment guards, and debug instrumentation. This systematic approach ensures that even if one layer is compromised, subsequent layers prevent catastrophic failures, making critical bugs structurally impossible to reproduce and providing clear forensic data for debugging.

Key Features

Four-layer validation architecture (Entry, Business, Environment, Debug)
Detailed debug instrumentation and forensic logging
Structural bug prevention strategies
Data flow mapping and checkpoint identification
Environment-specific safety guards for dangerous operations
4 GitHub stars

Use Cases

Hardening API boundaries against malformed or malicious input across multiple services
Preventing destructive operations like unintended file deletions or git initializations
Enforcing strict environment isolation to prevent test data from affecting production

About

Key Features

Four-layer validation architecture (Entry, Business, Environment, Debug)
Detailed debug instrumentation and forensic logging
Structural bug prevention strategies
Data flow mapping and checkpoint identification
Environment-specific safety guards for dangerous operations
4 GitHub stars

Use Cases

Hardening API boundaries against malformed or malicious input across multiple services
Preventing destructive operations like unintended file deletions or git initializations
Enforcing strict environment isolation to prevent test data from affecting production