Interview Q&A

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 the request was successful, and the server is returning the expected response body (e.g., GET request returning data).

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 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: 404 Not Found → The resource does not exist (or the client requested the wrong endpoint). 410 Gone → The resource used to exist but has been permanently removed.

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 indicates a server-side failure (unexpected error, crash, or unhandled exception). It’s a generic error and should be logged for debugging.

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 indicates the request was well-formed (valid syntax) but could not be processed due to semantic errors. 👉 Example: Submitting a form where email is valid format but already exists.

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.

Answer: It indicates the server timed out waiting for the client’s request. 👉 Example: Client took too long to send data in a POST request.

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: 503 indicates the server is temporarily unavailable (e.g., maintenance, overload). Best practices: Return a Retry-After header. Use monitoring/alerts to restore service quickly.

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: 401 Unauthorized → Authentication required (client not logged in / invalid token). 403 Forbidden → Authentication is valid, but the user lacks permissions.

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: A redirect tells the client to fetch a resource from a different URL. 301 Moved Permanently → Resource moved permanently (update bookmarks/links). 302 Found → Temporary redirect (use current URL for future requests).

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.

Statelessness means each client request to the server must contain all the necessary

information to process it (like authentication token, parameters, body). The server does not

store client session state.

👉 Example in ASP.NET Core Web API:

[HttpGet("profile")]

public IActionResult GetProfile([FromHeader] string token)
{
if (string.IsNullOrEmpty(token)) return Unauthorized();

// Token is validated each time (stateless, no session memory)

return Ok(new { Name = "John Doe", Email = "john@example.com"

});

}

It means REST APIs separate the client (frontend/UI) and server (backend logic,

database).

• The client is responsible for UI and user interactions.
• The server manages data, business logic, and security.

This separation improves scalability and flexibility.

👉 Example:

• Client: React.js front-end making API calls.
• Server: ASP.NET Core Web API handling requests.

Responses from the server should indicate whether they are cacheable or not, to improve

performance and scalability. Clients and intermediaries can reuse cached responses.

👉 Example in ASP.NET Core:

[HttpGet("products")]

[ResponseCache(Duration = 60)] // Cache for 60 seconds

public IActionResult GetProducts()
{
return Ok(new[] { "Laptop", "Mouse", "Keyboard" });
}

The uniform interface ensures that REST APIs follow consistent conventions for

communication, making them predictable and easy to use.

Key aspects:

• Use of standard HTTP methods (GET, POST, PUT, DELETE).
• Resource identification via URIs.
• Resource representations (JSON, XML).
• Self-descriptive messages.

In REST, resources (like users, products, orders) are identified with URLs instead of

ctions.

👉 Example in ASP.NET Core Web API:

// Instead of action-based

GET /getUser?id=1

// Use resource-based

GET /users/1

This makes APIs cleaner and more intuitive.

• Statelessness → No server memory required for client sessions → Easy to scale

horizontally.

• Layered System → Load balancers, caching layers can be added without changing

PI.

• Uniform Interface → Predictable, decouples client and server.
• Cacheability → Reduces server load.

Each request and response should have enough metadata (headers, content type, status

codes) to describe how to process it, without external context.

👉 Example in ASP.NET Core:

return Ok(new
{

Id = 1,

Name = "John",

Links = new[] { new { Rel = "self", Href = "/users/1" } }

});

Here, the response describes itself (content type = JSON, includes resource links).

Discoverability means clients can navigate and learn available actions through metadata

or hypermedia links, without hardcoding routes.

👉 Example using HATEOAS in ASP.NET Core Web API:

[HttpGet("users/{id}")]

public IActionResult GetUser(int id)
{
var user = new { Id = id, Name = "Alice" };
var response = new
{

user,

links = new[]

{

new { rel = "self", href = Url.Action("GetUser", new {

id }) },

new { rel = "orders", href = Url.Action("GetUserOrders",

new { id }) }

}

};

return Ok(response);
}

The API response itself guides the client to related resources (user’s orders, profile, etc.).

Q&A

• Use resource-based URLs (/users/1/orders) not action-based

(/getUserOrders).

• ● Return proper status codes (200, 201, 400, 404, 500).
• Support pagination & filtering for large data.
• Implement authentication & authorization (JWT, OAuth2).
• Ensure statelessness.
• Provide versioning (v1, v2).
• Secure API with HTTPS only.

Answer: Use nouns, not verbs → GET /users (not /getUsers). Use plural form → /users, /orders. Nested resources for relationships → /users/1/orders. Consistent naming conventions. Avoid exposing internal DB structure.

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.