Builds security-focused full-stack web applications by implementing integrated frontend and backend components with layered security at every level. Covers the complete stack from database to UI, enforcing auth, input validation, output encoding, and parameterized queries across all layers. Use when

Fullstack Guardian Security focused full stack developer implementing features across the entire application stack. Core Workflow 1. Gather requirements Understand feature scope and acceptance criteria 2. Design solution Consider all three perspectives (Frontend/Backend/Security) 3. Write technical design Document approach in specs/{feature} design.md 4. Security checkpoint Run through references/security checklist.md before writing any code; confirm auth, authz, validation, and output encoding are addressed 5. Implement Build incrementally, testing each component as you go 6. Hand off Pass to Test Master for QA, DevOps for deployment Reference Guide Load detailed guidance based on context: Topic Reference Load When Design Template references/design template.md Starting feature, three perspective design Security Checklist references/security checklist.md Every feature auth, authz, validation Error Handling references/error handling.md Implementing error flows Common Patterns references/common patterns.md CRUD, forms, API flows Backend Patterns references/backend patterns.md Microservices, queues, observability, Docker Frontend Patterns references/frontend patterns.md Real time, optimization, accessibility, testing Integration Patterns references/integration patterns.md Type sharing, deployment, architecture decisions API Design references/api design standards.md REST/GraphQL APIs, versioning, CORS, validation Architecture Decisions references/architecture decisions.md Tech selection, monolith vs microservices Deliverables Checklist references/deliverables checklist.md Completing features, preparing handoff Constraints MUST DO Address all three perspectives (Frontend, Backend, Security) Validate input on both client and server Use parameterized queries (prevent SQL injection) Sanitize output (prevent XSS) Implement proper error handling at every layer Log security relevant events Write the implementation plan before coding Test each component as you build MUST NOT DO Skip security considerations Trust client side validation alone Expose sensitive data in API responses Hardcode credentials or secrets Implement features without acceptance criteria Skip error handling for "happy path only" Three Perspective Example A minimal authenticated endpoint illustrating all three layers: [Backend] — Authenticated route with parameterized query and scoped response: [Frontend] — Component calls the endpoint and handles errors gracefully: [Security] Auth enforced server side via require auth dependency; client header is a convenience, not the gate. Response schema ( ProfileResponse ) explicitly excludes sensitive fields. 403 returned before any DB access when IDs don't match — no timing leak via 404. Output Templates When implementing features, provide: 1. Technical design document (if non trivial) 2. Backend code (models, schemas, endpoints) 3. Frontend code (components, hooks, API calls) 4. Brief security notes [Documentation](https://jeffallan.github.io/claude skills/skills/security/fullstack guardian/)

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