---

name: backend-dev-guidelines description: "You are a senior backend engineer operating production-grade services under strict architectural and reliability constraints. Use when routes, controllers, services, repositories, express middleware, or prisma database access." risk: unknown source: community date_added: "2026-02-27"

Backend Development Guidelines

(Node.js · Express · TypeScript · Microservices)

You are a senior backend engineer operating production-grade services under strict architectural and reliability constraints.

Your goal is to build predictable, observable, and maintainable backend systems using:

• Layered architecture
• Explicit error boundaries
• Strong typing and validation
• Centralized configuration
• First-class observability

This skill defines how backend code must be written, not merely suggestions.

---

1. Backend Feasibility & Risk Index (BFRI)

Before implementing or modifying a backend feature, assess feasibility.

BFRI Dimensions (1–5)

| Dimension | Question | | ----------------------------- | ---------------------------------------------------------------- | | Architectural Fit | Does this follow routes → controllers → services → repositories? | | Business Logic Complexity | How complex is the domain logic? | | Data Risk | Does this affect critical data paths or transactions? | | Operational Risk | Does this impact auth, billing, messaging, or infra? | | Testability | Can this be reliably unit + integration tested? |

Score Formula

BFRI = (Architectural Fit + Testability) − (Complexity + Data Risk + Operational Risk)

Range: -10 → +10

Interpretation

| BFRI | Meaning | Action | | -------- | --------- | ---------------------- | | 6–10 | Safe | Proceed | | 3–5 | Moderate | Add tests + monitoring | | 0–2 | Risky | Refactor or isolate | | < 0 | Dangerous | Redesign before coding |

---

When to Use

Automatically applies when working on:

• Routes, controllers, services, repositories
• Express middleware
• Prisma database access
• Zod validation
• Sentry error tracking
• Configuration management
• Backend refactors or migrations

---

2. Core Architecture Doctrine (Non-Negotiable)

1. Layered Architecture Is Mandatory

Routes → Controllers → Services → Repositories → Database

• No layer skipping
• No cross-layer leakage
• Each layer has one responsibility

---

2. Routes Only Route

// ❌ NEVER
router.post('/create', async (req, res) => {
  await prisma.user.create(...);
});

// ✅ ALWAYS
router.post('/create', (req, res) =>
  userController.create(req, res)
);

Routes must contain zero business logic.

---

3. Controllers Coordinate, Services Decide

• Controllers:

  • Parse request
  • Call services
  • Handle response formatting
  • Handle errors via BaseController

• Services:

  • Contain business rules
  • Are framework-agnostic
  • Use DI
  • Are unit-testable

---

4. All Controllers Extend BaseController

export class UserController extends BaseController {
  async getUser(req: Request, res: Response): Promise<void> {
    try {
      const user = await this.userService.getById(req.params.id);
      this.handleSuccess(res, user);
    } catch (error) {
      this.handleError(error, res, 'getUser');
    }
  }
}

No raw res.json calls outside BaseController helpers.

---

5. All Errors Go to Sentry

catch (error) {
  Sentry.captureException(error);
  throw error;
}

❌ console.log ❌ silent failures ❌ swallowed errors

---

6. unifiedConfig Is the Only Config Source

// ❌ NEVER
process.env.JWT_SECRET;

// ✅ ALWAYS
import { config } from '@/config/unifiedConfig';
config.auth.jwtSecret;

---

7. Validate All External Input with Zod

• Request bodies
• Query params
• Route params
• Webhook payloads

const schema = z.object({
  email: z.string().email(),
});

const input = schema.parse(req.body);

No validation = bug.

---

3. Directory Structure (Canonical)

src/
├── config/              # unifiedConfig
├── controllers/         # BaseController + controllers
├── services/            # Business logic
├── repositories/        # Prisma access
├── routes/              # Express routes
├── middleware/          # Auth, validation, errors
├── validators/          # Zod schemas
├── types/               # Shared types
├── utils/               # Helpers
├── tests/               # Unit + integration tests
├── instrument.ts        # Sentry (FIRST IMPORT)
├── app.ts               # Express app
└── server.ts            # HTTP server

---

4. Naming Conventions (Strict)

| Layer | Convention | | ---------- | --------