Interview Q&A

A REST (Representational State Transfer) API is an architectural style for designing

networked applications. It uses HTTP methods (GET, POST, PUT, DELETE) to perform

operations on resources identified by URLs (endpoints). Data is usually exchanged in JSON

or XML format.

Answer: Return a structured JSON response with: status → HTTP status code error → Short message details → Optional for debugging Example: "status": 400, "error": "Bad Request", "details": "Email is required"

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: HTTP provides the transport mechanism and defines methods: GET → Retrieve data POST → Create resource PUT → Update resource DELETE → Remove resource PATCH → Partial update

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: An endpoint is a specific URL that represents a resource in a REST API. 👉 Example: → Represents user with ID 1.

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: In REST, everything is modeled as a resource (users, products, orders). Each resource is identified by a URI and can be manipulated using standard HTTP methods.

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: Middleware is software that sits between client requests and server responses. Used for: Logging Authentication & Authorization Request validation Error handling Rate limiting

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: Idempotency means multiple identical requests have the same effect as one. PUT → Updating a resource with the same data multiple times results in no further change. DELETE → Deleting a resource repeatedly still results in it being deleted.

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 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: 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 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 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: 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.

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"

});

}

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.

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).

Answer: Versioning ensures backward compatibility when APIs change. Common approaches: URI versioning → /api/v1/users Header-based versioning → Accept: application/vnd.myapi.v1+json Query parameter → /users?version=1

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: Lightweight and easy to parse. Language independent. Human-readable. Supported natively by JavaScript and most frameworks.

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: Use throttling to limit requests per minute/hour per client. Return 429 Too Many Requests. Provide Retry-After header. Tools: API Gateway, NGINX, Middleware.

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: An API key is a unique token used to authenticate requests. 👉 Example: GET /users?apikey=12345 Best practice: Send in headers → Authorization: ApiKey 12345.

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: Synchronous → Client waits until the server responds (blocking). Asynchronous → Server processes request in background and may send response later (via polling, callbacks, or webhooks).

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: Used for CORS preflight requests. Tells the client which HTTP methods and headers are allowed. 👉 Example Response: llow: GET, POST, PUT, DELETE ccess-Control-Allow-Origin: *

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.

• Provides clear usage guidelines for developers.
• Reduces onboarding time for new teams.
• Ensures consistency across different services.
• Helps with discoverability of endpoints, parameters, request/response formats.

👉 Tools: Swagger (OpenAPI), Postman, Redoc.

rchitecture?

• API Gateway is a single entry point for APIs in a microservices architecture.
• Handles routing, load balancing, authentication, rate limiting, logging,

monitoring.

• Examples: Kong, NGINX, AWS API Gateway, Azure API Management.
• Use when:
• You have multiple microservices.
• Need centralized authentication/security.
• Need rate limiting or monitoring.