senior-backend

The saved excerpt is a snapshot from review. The external source remains the complete and most current version.

---
name: "senior-backend"
description: Designs and implements backend systems including REST APIs, microservices, database architectures, authentication flows, and security hardening. Use when the user asks to "design REST APIs", "optimize database queries", "implement authentication", "build microservices", "review backend code", "set up GraphQL", "handle database migrations", or "load test APIs". Covers Node.js/Express/Fastify development, PostgreSQL optimization, API security, and backend architecture patterns.
---

# Senior Backend Engineer

Backend development patterns, API design, database optimization, and security practices.

---

## Quick Start

```bash
# Generate API routes from OpenAPI spec
python scripts/api_scaffolder.py openapi.yaml --framework express --output src/routes/

# Analyze database schema and generate migrations
python scripts/database_migration_tool.py --connection postgres://localhost/mydb --analyze

# Load test an API endpoint
python scripts/api_load_tester.py https://api.example.com/users --concurrency 50 --duration 30
```

---

## Tools Overview

### 1. API Scaffolder

Generates API route handlers, middleware, and OpenAPI specifications from schema definitions.

**Input:** OpenAPI spec (YAML/JSON) or database schema
**Output:** Route handlers, validation middleware, TypeScript types

**Usage:**
```bash
# Generate Express routes from OpenAPI spec
python scripts/api_scaffolder.py openapi.yaml --framework express --output src/routes/
# Output: Generated 12 route handlers, validation middleware, and TypeScript types

# Generate from database schema
python scripts/api_scaffolder.py --from-db postgres://localhost/mydb --output src/routes/

# Generate OpenAPI spec from existing routes
python scripts/api_scaffolder.py src/routes/ --generate-spec --output openapi.yaml
```

**Supported Frameworks:**
- Express.js (`--framework express`)
- Fastify (`--framework fastify`)
- Koa (`--framework koa`)

---

### 2. Database Migration Tool

Analyzes database schemas, detects changes, and generates migration files with rollback support.

**Input:** Database connection string or schema files
**Output:** Migration files, schema diff report, optimization suggestions

**Usage:**
```bash
# Analyze current schema and suggest optimizations
python scripts/database_migration_tool.py --connection postgres://localhost/mydb --analyze
# Output: Missing indexes, N+1 query risks, and suggested migration files

# Generate migration from schema diff
python scripts/database_migration_tool.py --connection postgres://localhost/mydb \
  --compare schema/v2.sql --output migrations/

# Dry-run a migration
python scripts/database_migration_tool.py --connection postgres://localhost/mydb \
  --migrate migrations/20240115_add_user_indexes.sql --dry-run
```

---

### 3. API Load Tester

Performs HTTP load testing with configurable concurrency, measuring latency percentiles and throughput.

**Input:** API endpoint URL and test configuration
**Output:** Performance report with latency distribution, error rates, throughput metrics

**Usage:**
```bash
# Basic load test
python scripts/api_load_tester.py https://api.example.com/users --concurrency 50 --duration 30
# Output: Throughput (req/sec), latency percentiles (P50/P95/P99), error counts, and scaling recommendations

# Test with custom headers and body
python scripts/api_load_tester.py https://api.example.com/orders \
  --method POST \
  --header "Authorization: Bearer token123" \
  --body '{"product_id": 1, "quantity": 2}' \
  --concurrency 100 \
  --duration 60

# Compare two endpoints
python scripts/api_load_tester.py https://api.example.com/v1/users https://api.example.com/v2/users \
  --compare --concurrency 50 --duration 30
```

---

## Backend Development Workflows

### API Design Workflow

Use when designing a new API or refactoring existing endpoints.

**Step 1: Define resources and operations**
```yaml
# openapi.yaml
openapi: 3.0.3
info:
  title: User Service API
  version: 1.0.0
path