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.
- 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 2. When to Use This Skill
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 3. 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.
- 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
No raw res.json calls outside BaseController helpers.
- All Errors Go to Sentry catch (error) { Sentry.captureException(error); throw error; }
❌ console.log ❌ silent failures ❌ swallowed errors
- unifiedConfig Is the Only Config Source // ❌ NEVER process.env.JWT_SECRET;
// ✅ ALWAYS import { config } from '@/config/unifiedConfig'; config.auth.jwtSecret;
- 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.
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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
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Naming Conventions (Strict) Layer Convention Controller PascalCaseController.ts Service camelCaseService.ts Repository PascalCaseRepository.ts Routes camelCaseRoutes.ts Validators camelCase.schema.ts
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Dependency Injection Rules Services receive dependencies via constructor No importing repositories directly inside controllers Enables mocking and testing export class UserService { constructor( private readonly userRepository: UserRepository ) {} }
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Prisma & Repository Rules
Prisma client never used directly in controllers
Repositories:
Encapsulate queries Handle transactions Expose intent-based methods await userRepository.findActiveUsers();
- Async & Error Handling asyncErrorWrapper Required
All async route handlers must be wrapped.
router.get( '/users', asyncErrorWrapper((req, res) => controller.list(req, res) ) );
No unhandled promise rejections.
- Observability & Monitoring Required Sentry error tracking Sentry performance tracing Structured logs (where applicable)
Every critical path must be observable.
- Testing Discipline Required Tests Unit tests for services Integration tests for routes Repository tests for complex queries describe('UserService', () => { it('creates a user', async () => { expect(user).toBeDefined(); }); });
No tests → no merge.
- Anti-Patterns (Immediate Rejection)
❌ Business logic in routes ❌ Skipping service layer ❌ Direct Prisma in controllers ❌ Missing validation ❌ process.env usage ❌ console.log instead of Sentry ❌ Untested business logic
- Integration With Other Skills frontend-dev-guidelines → API contract alignment error-tracking → Sentry standards database-verification → Schema correctness analytics-tracking → Event pipelines skill-developer → Skill governance
- Operator Validation Checklist
Before finalizing backend work:
BFRI ≥ 3 Layered architecture respected Input validated Errors captured in Sentry unifiedConfig used Tests written No anti-patterns present 14. Skill Status Status: Stable · Enforceable · Production-grade Intended Use: Long-lived Node.js microservices with real traffic and real risk