/senior-backend

name: "senior-backend"
description: "Build and fix backend services: REST or GraphQL APIs, auth, microservices, PostgreSQL queries, migrations and load tests. Use whenever the user's API is slow or broken, needs login or auth added, a schema change, or a new endpoint or service scaffolded."

Senior Backend Engineer

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

---

Quick Start

# 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:**

# 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:**

# 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:**

# 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**

# openapi.yaml
openapi: 3.0.3
info:
  title: User Service API
  version: 1.0.0
paths:
  /users:
    get:
      summary: List users
      parameters:
        - name: "limit"
          in: query
          schema:
            type: integer
            default: 20
    post:
      summary: Create user
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/CreateUser'

**Step 2: Generate route scaffolding**

python scripts/api_scaffolder.py openapi.yaml --framework express --output src/routes/

**Step 3: Implement business logic**

// src/routes/users.ts (generated, then customized)
export const createUser = async (req: Request, res: Response) => {
  const { email, name } = req.body;

  // Add business logic
  const user = await userService.create({ email, name });

  res.status(201).json(user);
};

**Step 4: Add validation middleware**

# Validation is auto-generated from OpenAPI schema
# src/middleware/validators.ts includes:
# - Request body validation
# - Query parameter validation
# - Path parameter validation

**Step 5: Generate updated OpenAPI spec**

python scripts/api_scaffolder.py src/routes/ --generate-spec --output openapi.yaml

---

Database Optimization Workflow

Use when queries are slow or database performance needs improvement.

**Step 1: Analyze current performance**

python scripts/database_migration_tool.py --connection $DATABASE_URL --analyze

**Step 2: Identify slow queries**

-- Check query execution plans
EXPLAIN ANALYZE SELECT * FROM orders
WHERE user_id = 123
ORDER BY created_at DESC
LIMIT 10;

-- Look for: Seq Scan (bad), Index Scan (good)

**Step 3: Generate index migrations**

python scripts/database_migration_tool.py --connection $DATABASE_URL \
  --suggest-indexes --output migrations/

**Step 4: Test migration (dry-run)**

python scripts/database_migration_tool.py --connection $DATABASE_URL \
  --migrate migrations/add_indexes.sql --dry-run

**Step 5: Apply and verify**

# Apply migration
python scripts/database_migration_tool.py --connection $DATABASE_URL \
  --migrate migrations/add_indexes.sql

# Verify improvement
python scripts/database_mig