NestJS

Structure the application around modules that represent business capabilities, not arbitrary folders.

Keep controllers focused on HTTP transport while services carry actual domain behavior.

Use dependency injection to make orchestration, testing and replacement of collaborators predictable.

Treat the framework as a system boundary tool instead of a decorative layer over unstructured code.

Expose APIs that can serve public websites, mobile applications, admin dashboards and internal workflows.

Keep authentication, permissions, business rules and side effects consistent across all entry points.

Design modules so product growth does not automatically create a monolithic service with hidden dependencies.

Prepare the backend for later concerns such as notifications, audit logs, billing, media, support and analytics.

Define module boundaries around business language: users, auth, billing, chat, claims, wallet or gamification.

Expose clear public services instead of allowing every module to reach into every other module directly.

Split facades, readers, orchestrators and domain services when the complexity justifies it.

Avoid giant services that validate input, execute queries, trigger events and format responses at the same time.

Use DTOs to define the accepted shape of public inputs instead of trusting raw request bodies.

Keep Swagger descriptions, examples, status codes and validation decorators consistent.

Document error responses and edge cases so API consumers can integrate without guessing.

Use OpenAPI verification tools such as Schemathesis to detect drift between documentation and implementation.

Use guards to enforce authentication, roles, ownership and sensitive access rules explicitly.

Validate all public inputs and avoid weakening DTOs just to make tests or demos pass.

Keep business errors stable, readable and safe to expose through public APIs.

Protect sensitive flows such as login, refresh tokens, admin access, billing, uploads and account changes.

Use Prisma transactions for workflows that must commit several related changes together.

Keep idempotency keys, source references and unique constraints close to the business rule they protect.

Avoid hiding important persistence decisions behind generic helper functions that make intent harder to review.

Verify query shapes, selected fields, ordering, filtering and transactional branches through targeted tests.

Keep WebSocket gateways thin and push domain behavior into services or orchestrators.

Separate immediate API responses from side effects such as notifications, emails, analytics and audit logs.

Design event names, payloads and delivery rules as contracts, not casual implementation details.

Make realtime behavior observable enough to debug chat, presence, support and admin workflows.

Write unit tests for service decisions, exception paths, guards, DTOs and fallback branches.

Use integration and E2E tests for real module collaboration, database behavior and public HTTP flows.

Run Schemathesis against the OpenAPI contract, k6 for performance signals and OWASP ZAP for exposed surfaces.

Use Stryker mutation testing to prove that assertions detect regressions instead of only executing code.

The codebase can absorb new product rules without rewriting unrelated modules.

Security, validation, transactions and access rules remain strong even when tests fail.

The repository exposes clear scripts for typecheck, lint, build, tests, contracts, smoke checks and mutation testing.

A new developer can understand the module boundaries, run the quality chain and modify one feature without breaking the platform.