Interview Q&A

• Statelessness → Each request is independent; the server doesn’t store client state.
• Client-Server Architecture → Separation of concerns between client UI and server

logic.

• Uniform Interface → Standard HTTP methods and URIs.
• Cacheable → Responses can be cached to improve performance.
• Layered System → APIs can use intermediaries (like load balancers, proxies).
• Resource-based → Everything is treated as a resource (like users, orders,

products).

uthorization: Bearer <token>

What interviewers expect

• A clear definition tied to REST API in ASP.NET Web API projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Web API application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Web API architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

Client sends token in Authorization header: Authorization: Bearer <token>

What interviewers expect

• A clear definition tied to REST API in ASP.NET Web API projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Web API application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Web API architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

Answer: REST → Lightweight, uses HTTP, usually JSON, easy to use, stateless. SOAP → Protocol-based, uses XML, more complex, built-in security & transactions. REST is more flexible and widely used for web and mobile apps.

What interviewers expect

• A clear definition tied to REST API in ASP.NET Web API projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Web API application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Web API architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

• Structured logging with libraries like Serilog, NLog, or built-in ILogger.
• Log requests and responses, including headers and payloads (avoid sensitive info).
• Use correlation IDs to trace requests across services.
• Centralize logs using ELK Stack, Seq, or Azure Application Insights.
• Log different levels: Information, Warning, Error, Critical.

Example using ILogger in ASP.NET Core:

private readonly ILogger<MyController> _logger;

public MyController(ILogger<MyController> logger)

_logger = logger;

[HttpGet("{id}")]

public IActionResult GetUser(int id)

_logger.LogInformation("Fetching user with id {UserId}", id);

try

var user = dbContext.Users.Find(id);

if (user == null)

_logger.LogWarning("User with id {UserId} not found",

id);

return NotFound();

return Ok(user);

catch (Exception ex)

_logger.LogError(ex, "Error fetching user with id {UserId}",

id);

return StatusCode(500, "Internal Server Error");

This covers all core aspects of error handling and debugging for REST APIs.

Answer: Stateless means the server does not store client session data. Each request must contain all the necessary information (like authentication tokens). This makes APIs scalable nd reliable.

What interviewers expect

• A clear definition tied to REST API in ASP.NET Web API projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Web API application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Web API architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

Answer: Platform-independent (works across web, mobile, IoT). Simple, flexible, and scalable. Uses existing HTTP infrastructure. Lightweight (JSON/XML). Supports caching for better performance.

What interviewers expect

• A clear definition tied to REST API in ASP.NET Web API projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Web API application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Web API architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

Answer: Easier to learn &amp; implement. Supports multiple formats (JSON, XML, plain text). Faster (less overhead). Works seamlessly with modern web &amp; mobile apps. Better performance due to caching &amp; statelessness.

What interviewers expect

• A clear definition tied to REST API in ASP.NET Web API projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Web API application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Web API architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

Suppose we have a User Service API:

• GET /users → Get all users
• GET /users/1 → Get user with ID=1
• POST /users → Create a new user
• PUT /users/1 → Update user with ID=1
• DELETE /users/1 → Delete user with ID=1

This shows how CRUD operations map directly to HTTP methods.

HATEOAS (Hypermedia As The Engine Of Application State) means responses contain

links to related actions/resources.

👉 Example:

{

"id": 1,

"name": "John",

"links": [

{ "rel": "self", "href": "/users/1" },

{ "rel": "orders", "href": "/users/1/orders" }

}

This helps clients navigate APIs dynamically.

Answer: Common methods: API Keys → Simple tokens. Basic Auth → Username &amp; password (not secure without HTTPS). OAuth 2.0 / OpenID Connect → Standard protocols for secure access. JWT (JSON Web Tokens) → Widely used for stateless authentication.

What interviewers expect

• A clear definition tied to REST API in ASP.NET Web API projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Web API application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Web API architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

Answer: GET → Used to retrieve data, should not modify server state, and can be cached/bookmarked. POST → Used to create new resources or submit data. It modifies server state, is not idempotent, and cannot be cached.

What interviewers expect

• A clear definition tied to REST API in ASP.NET Web API projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Web API application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Web API architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

Answer: 200 OK → If the resource was successfully deleted and a response body is returned. 204 No Content → If the resource was deleted but no body is needed. 404 Not Found → If the resource does not exist.

What interviewers expect

• A clear definition tied to REST API in ASP.NET Web API projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Web API application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Web API architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

Answer: Safe → Because it only retrieves data without modifying server state. Idempotent → Multiple GET requests have the same result; no side effects occur.

What interviewers expect

• A clear definition tied to REST API in ASP.NET Web API projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Web API application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Web API architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

Answer: Yes. If the resource does not exist, PUT can create it at the specified URI. Example: 👉 PUT /users/100 → If user 100 doesn’t exist, it will be created.

What interviewers expect

• A clear definition tied to REST API in ASP.NET Web API projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Web API application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Web API architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

• PATCH → Updates only the specified fields (partial update).
• PUT → Replaces the entire resource representation.

👉 Example:

• PATCH /users/1 { "email": "new@email.com" } → Updates only the

email.

• PUT /users/1 { "name": "John" } → May overwrite other fields like email if

not included.

Answer: PI? The GET method is used to fetch data because it is safe, idempotent, and optimized for retrieval operations.

What interviewers expect

• A clear definition tied to REST API in ASP.NET Web API projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Web API application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Web API architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

Answer: The GET method is used to fetch data because it is safe, idempotent, and optimized for retrieval operations. 🔹 HTTP Status Codes – REST API Interview Q&amp;A

What interviewers expect

• A clear definition tied to REST API in ASP.NET Web API projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Web API application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Web API architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

PIs?

HTTP status codes are 3-digit numbers returned by the server to indicate the result of a

client request.

They are important because they:

• Communicate success, failure, or redirection.
• Help clients handle responses consistently.
• Provide debugging and monitoring information.

HTTP status codes are 3-digit numbers returned by the server to indicate the result of a

client request.

They are important because they:

• Communicate success, failure, or redirection.
• Help clients handle responses consistently.
• Provide debugging and monitoring information.

Answer: It indicates that a new resource was successfully created. Usually returned after a POST request, along with a Location header pointing to the new resource.

What interviewers expect

• A clear definition tied to REST API in ASP.NET Web API projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Web API application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Web API architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

Answer: Returned when the request is malformed or invalid, such as: Missing required parameters. Invalid JSON format. Wrong data type provided.

What interviewers expect

• A clear definition tied to REST API in ASP.NET Web API projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Web API application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Web API architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

Answer: It means the client is not authenticated (missing/invalid credentials). The request cannot proceed without proper authentication (e.g., missing token).

What interviewers expect

• A clear definition tied to REST API in ASP.NET Web API projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Web API application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Web API architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

Answer: It means the client is authenticated but not authorized to access the resource. 👉 Example: A normal user trying to access an admin-only endpoint.

What interviewers expect

• A clear definition tied to REST API in ASP.NET Web API projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Web API application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Web API architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

Answer: It means the resource has not changed since the last request. Commonly used with caching to improve performance (client uses cached version).

What interviewers expect

• A clear definition tied to REST API in ASP.NET Web API projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Web API application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Web API architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.