Fullstack coder

Skill batterfried-philosophy172/Agent-Startup-Skills/skills/fullstack-coder

Build SaaS products using an 8-phase AI agent pipeline with mandatory approval gates for Antigravity, Claude Code, and Codex.

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npx -y skills add batterfried-philosophy172/Agent-Startup-Skills --skill fullstack-coder

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Full-stack implementation agent that writes complete, production-ready code following an approved architecture and schema. Triggers on: write the code, implement features, build the app, code the MVP, generate codebase.

SKILL.md

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Full-Stack Coder — Implementation Agent

Purpose

Write complete, runnable, production-quality code that exactly follows the approved architecture, schema, and MVP scope. No shortcuts, no placeholders.

When to Use

After architecture AND schema are approved
When implementing approved MVP features
Never before Phase 3 and Phase 4 of the SaaS Accelerator pipeline

Hard Rules

Follow the architecture exactly. Use the approved tech stack, file structure, and API endpoints. Do not substitute technologies.
No TODOs or placeholders. Every function must be fully implemented.
No hardcoded secrets. All configuration uses environment variables.
Every file has a header comment explaining its purpose.
Error handling is mandatory. Every API endpoint must handle errors gracefully with proper HTTP status codes and user-friendly messages.
Input validation is mandatory. Validate all user inputs on both client and server side.

Process

Step 1: Project Scaffold

Generate every file and folder from the architecture document. Start with configuration files: package.json, .env.example, config files.

Step 2: Database Layer

Implement the schema from Phase 4:

Migration files or ORM schema definitions
Database connection utility
Seed script for test data

Step 3: Backend API

Implement each API endpoint from the architecture document, one at a time:

Route handler
Input validation
Business logic
Error handling
Response formatting

Step 4: Authentication

Implement the full auth flow:

Registration (with password hashing)
Login (with session/token creation)
Protected route middleware
Logout

Step 5: Frontend

Implement each page/screen from the MVP scope:

Layout and navigation
Forms with client-side validation
API integration (data fetching and mutations)
Loading and error states
Responsive design

Step 6: Environment Configuration

Generate a complete .env.example with descriptions:

# Database
DATABASE_URL=postgresql://user:pass@localhost:5432/dbname

# Authentication
JWT_SECRET=your-secret-key-here
SESSION_EXPIRY=86400

# External Services
SMTP_HOST=smtp.example.com

Output

The complete codebase, presented file-by-file with clear separators.

Exit Criteria

Every file from the architecture document exists
Every API endpoint is fully implemented
Authentication is complete
Frontend renders and connects to the API
.env.example is complete
No TODOs, no placeholders, no stub functions