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Next.js provides two routing systems: the Pages Router organizes page files, while the App Router uses nested route segments, layouts and React Server Components. They have different data-fetching and rendering conventions. Knowing which router a project uses prevents mixing APIs and assumptions from different architectures.

The interviewer first needs a clear picture of what the product does and who uses it. Introduce the business domain before listing frameworks so the technical discussion has context. A short project summary should be understandable to someone outside your team.

A problem statement explains the user's difficulty or business need that motivated the feature. It should distinguish the problem from your implementation choice: “using NestJS” is not a user problem. Explain the previous limitation only if you know it from the actual project.

A technology answer should explain how each tool helped implement the project. Listing names alone does not show whether you used the tool or understood its purpose. Choose the relevant tools and connect them to HTTP handling, persistence, authentication, integration or deployment.

Failure scenarios are the ways a normal workflow can be interrupted or produce an uncertain result. They include invalid data, unavailable dependencies, duplicate events and crashes between steps. A project answer should explain the scenarios the actual system handled and honestly identify known gaps.

Application security is a collection of controls at identity, data-access, input and operational boundaries. A project explanation should focus on specific implemented checks rather than broad labels such as “secure APIs.” Use one concrete request to demonstrate how an unauthorized action was rejected.

A difficult-problem answer should show how you reasoned under a real constraint, not simply that a project had many features. Pick one problem where your investigation or decision changed the outcome. Keep the story focused enough that you can defend each technical detail.

Your role describes the decisions and implementation work you personally owned. Interviewers use it to choose follow-up questions and separate individual depth from team-wide scope. Being precise makes a modest contribution easier to defend than an inflated claim about the whole system.

A technology decision is a trade-off between requirements, team knowledge, existing systems and operating costs. Sometimes you selected the tool; sometimes you inherited it and made good use of it. Both are valid experiences when clearly distinguished.

API structure describes how a request moves from the client through validation and access checks to business logic and persistence. It also includes resource names, error contracts and how responsibilities are separated. A real endpoint example makes the structure easier to understand than a folder list.

Data modeling identifies the records, relationships and constraints needed to represent the business correctly. A model should support the important reads and prevent invalid writes. Explain it through a real workflow so each table, document or relationship has a reason to exist.

Authentication flow explains how the system establishes and maintains the caller's identity. It includes the login method, credential validation and how subsequent API requests are recognized. Authorization follows from that identity but must be described separately.

Error handling defines what happens when inputs, business rules or dependencies fail. A reliable API returns an appropriate response while preserving enough internal context for diagnosis. The answer should describe actual behavior rather than promise that errors were simply “handled centrally.”