Web API Interview Questions for beginners & Answers (2025)

The Same-Origin Policy is a security measure that restricts web pages from making requests to a different domain than the one that served the web page. This affects cross-origin API requests.

A Web API (Application Programming Interface) is a set of protocols and tools that allows different software applications to communicate with each other over the internet.

Some key characteristics include being easy to use, well-documented, consistent, secure, and scalable.

JSON is a lightweight data-interchange format. It's commonly used in Web APIs to structure and transmit data between the server and client.

A client application communicates with a Web API by sending HTTP requests (GET, POST, PUT, DELETE) to specific API endpoints, and the API responds with the requested data.

An API endpoint is a specific URL where an API can be accessed. Each endpoint represents a specific resource or functionality provided by the API.

HTTP methods define the type of operation to be performed on a resource. GET retrieves data, POST creates new data, PUT updates data, and DELETE removes data.

Authentication verifies the identity of a user or application, while authorization determines what actions they're allowed to perform. Common methods include API keys, OAuth, and tokens.

CORS (Cross-Origin Resource Sharing) is a security feature that controls which origins are allowed to access resources from a different origin. It prevents unauthorized cross-origin requests.

Errors can be communicated using appropriate HTTP status codes and by providing meaningful error messages in the response body.

Stateless communication doesn't rely on server-side memory to store the client state. Each request from the client contains all the necessary information. Stateful communication, on the other hand, maintains the client state on the server.

Caching involves storing frequently requested data on the client or server side, reducing the need to repeatedly fetch the same data from the source.

Data model versioning can be achieved by including version information in the data structures, using namespaces, or employing backward-compatible changes.

A Webhook is a way for an API to notify another application about events that have occurred. It involves the API sending data to a URL specified by the receiving application.

An operation is idempotent if performing it multiple times has the same effect as performing it once. For example, sending the same DELETE request multiple times should result in the same outcome as sending it once.

Comprehensive and clear API documentation helps developers understand how to use the API effectively, reducing errors and accelerating development.

An API Gateway is a server that acts as an intermediary between clients and a collection of microservices or backend services. It can handle tasks like authentication, load balancing, and request routing.

Version negotiation involves the client and server agreeing on the version of the API to be used for communication. This can be done using request headers or URL parameters.

Pagination involves breaking up a large result set into smaller pages. The API can accept parameters like "page" and "page size" to specify which portion of the data the client wants to retrieve.

Content Negotiation is the process of determining the format in which the client wants to receive the response data. This can be done using the "Accept" header in the request.

OAuth 2.0 is an authorization framework that allows third-party applications to access user data without exposing the user's credentials. It involves granting access tokens to authorized applications.

Rate limiting restricts the number of requests a client can make within a certain time frame to prevent abuse and ensure fair usage, maintaining the API's performance and stability.

Validate input data for correctness and sanitize it to prevent security vulnerabilities like SQL injection and cross-site scripting (XSS).

The "If-Modified-Since" header is used in a conditional request to check whether a resource has been modified since a specific date. If not, the server can respond with a "304 Not Modified" status.

Data integrity can be ensured through mechanisms like using HTTPS for secure data transmission, implementing proper validation on both client and server sides, and employing cryptographic techniques.