In today’s fast-paced software development landscape, APIs (Application Programming Interfaces) play a crucial role in enabling applications to communicate and interact with each other. An API Developer is responsible for designing, developing, and maintaining APIs that allow different software systems to interact seamlessly. If you’re preparing for an API developer interview, it’s important to understand the technical aspects of APIs as well as the best practices involved in their development.
This article will cover some of the most common and critical API-related interview questions that are often asked to API Developer candidates. By understanding these questions and their answers, you’ll be better prepared for your next interview.
Table of Contents
Top Interview Questions for API Developer Job Profile
1. What is an API? Explain its different types.
Answer: An API (Application Programming Interface) is a set of rules and protocols that allow different software applications to communicate with each other. APIs expose a set of functions or methods that developers can use to interact with the software or service. They act as a bridge between different software systems, allowing them to exchange data and functionality.
There are several types of APIs:
- REST API: Representational State Transfer (REST) is an architectural style that uses HTTP methods to perform CRUD operations on resources. REST APIs are stateless and use standard HTTP methods like GET, POST, PUT, and DELETE.
- SOAP API: Simple Object Access Protocol (SOAP) is a protocol for exchanging structured information in the implementation of web services. It is more rigid than REST and typically uses XML for message format.
- GraphQL API: GraphQL is a query language for APIs and a runtime for executing queries against data. Unlike REST, where each endpoint returns a fixed set of data, GraphQL allows clients to request exactly the data they need.
- WebSocket API: WebSocket is a communication protocol that provides full-duplex communication channels over a single, long-lived connection. It is often used for real-time applications like chat and live updates.
- gRPC API: gRPC is an open-source remote procedure call (RPC) framework developed by Google. It uses Protocol Buffers (protobuf) as the interface definition language and is designed for high-performance, low-latency communication.
2. What is REST and how does it differ from SOAP?
Answer: REST (Representational State Transfer) is an architectural style that uses standard HTTP methods (GET, POST, PUT, DELETE) to perform operations on resources, which are identified by URLs. REST APIs are stateless, meaning each request from a client to the server must contain all the information needed to understand and process the request. REST APIs are often used for web services because of their simplicity and ease of use.
SOAP (Simple Object Access Protocol) is a protocol for exchanging structured information in web services. Unlike REST, SOAP requires more strict messaging formats, usually in XML, and often uses HTTP or SMTP for message transport. SOAP is more rigid than REST, and it provides higher security, transaction compliance, and reliability features (e.g., ACID transactions) but can be slower and more complex to implement.
Key differences:
- Protocol: SOAP is a protocol, while REST is an architectural style.
- Message Format: SOAP relies on XML for messaging, whereas REST can use XML, JSON, or other formats.
- State: REST is stateless, while SOAP can be stateful.
- Performance: REST is generally faster and more lightweight than SOAP.
- Complexity: SOAP has more built-in features, but it is more complex compared to REST.
3. What is the HTTP request-response cycle?
Answer: The HTTP request-response cycle is the process by which a client (usually a web browser or mobile app) sends a request to a server, and the server responds with the requested resource or an appropriate status code.
- Client sends a request: The client sends an HTTP request to the server. This request contains information such as the HTTP method (GET, POST, etc.), headers, and body (in the case of POST or PUT requests).
- Server processes the request: The server processes the request, which may involve querying a database, processing business logic, or performing other operations.
- Server sends a response: The server sends an HTTP response back to the client. The response includes a status code (e.g., 200 OK, 404 Not Found), headers, and the requested data (e.g., HTML, JSON, or XML).
- Client processes the response: The client processes the response and displays the data to the user or performs other actions based on the response.
4. What are HTTP methods? Explain their use.
Answer: HTTP methods (also known as HTTP verbs) define the action to be performed on the resource identified by the URL in an HTTP request. The most commonly used HTTP methods are:
- GET: Retrieves data from the server. It is a read-only operation and should not modify any data on the server.
- POST: Sends data to the server to create a new resource. It is used for form submissions or API calls that create new records.
- PUT: Updates an existing resource on the server. It replaces the entire resource with the data provided in the request body.
- PATCH: Similar to PUT, but it only updates a specific part of the resource rather than replacing it entirely.
- DELETE: Deletes a resource on the server.
- HEAD: Similar to GET, but it only retrieves the headers of the resource, not the body.
- OPTIONS: Returns the HTTP methods that the server supports for a specific resource.
5. What is authentication and authorization in the context of APIs?
Answer:
- Authentication is the process of verifying the identity of a user or system. In API development, authentication ensures that the requestor is who they claim to be. Common authentication methods include:
- Basic Authentication: Sending a username and password encoded in the HTTP header.
- OAuth: An open standard for access delegation that allows third-party services to access resources on behalf of the user without exposing their credentials.
- API Keys: A unique identifier sent with requests to verify the caller’s identity.
- Authorization is the process of determining whether an authenticated user has permission to access a specific resource. After a user is authenticated, the API determines if the user has the right to perform the requested action. This is usually done through roles and permissions.
6. What is CORS and how does it work?
Answer: CORS (Cross-Origin Resource Sharing) is a security feature implemented by browsers to prevent malicious websites from making unauthorized requests to another domain. It restricts how resources on a web server can be requested from another domain.
CORS works by adding special HTTP headers to responses from the server. These headers specify which domains are allowed to access the resources. If a client makes a cross-origin request, the browser checks these headers and allows or denies the request based on the allowed origins.
Key CORS headers include:
- Access-Control-Allow-Origin: Specifies which domains can access the resource.
- Access-Control-Allow-Methods: Specifies which HTTP methods are allowed for the resource.
- Access-Control-Allow-Headers: Specifies which HTTP headers can be used in the actual request.
7. What is API rate limiting? Why is it important?
Answer: API rate limiting is a technique used to control the number of requests a client can make to an API in a given period. This is important to prevent abuse, ensure fair usage, and protect the server from being overwhelmed by too many requests.
Common rate-limiting strategies include:
- Fixed Window: Limits the number of requests in a fixed time window (e.g., 100 requests per minute).
- Rolling Window: Similar to fixed window but the time window rolls with each request.
- Leaky Bucket: Allows requests at a steady rate but can handle bursts by accumulating excess requests in a “bucket.”
- Token Bucket: Allows bursts of traffic up to a certain limit but penalizes clients if too many requests are made in a short time.
Rate limiting is crucial for preventing Denial of Service (DoS) attacks, managing server load, and ensuring a good user experience for all users.
8. What is Swagger/OpenAPI?
Answer: Swagger (now known as OpenAPI Specification) is a framework for designing, building, and documenting RESTful APIs. It provides a standardized format (in JSON or YAML) for describing the API’s endpoints, request/response formats, authentication methods, and other relevant information.
Using Swagger, developers can:
- Generate interactive API documentation for end-users and clients.
- Automatically generate server and client code in multiple programming languages.
- Validate API specifications and test API endpoints.
9. What are the common security vulnerabilities in APIs?
Answer: Some of the most common security vulnerabilities in APIs include:
- SQL Injection: Exploiting vulnerabilities in the API to execute arbitrary SQL commands on the database.
- Cross-Site Scripting (XSS): Injecting malicious scripts into API responses, which are executed by the client’s browser.
- Cross-Site Request Forgery (CSRF): Trick users into making requests on behalf of an attacker.
- Insecure Direct Object References (IDOR): Allowing users to access unauthorized data by manipulating URL parameters or request bodies.
- Sensitive Data Exposure: Sending sensitive information like passwords, API keys, or tokens in an insecure way (e.g., over HTTP instead of HTTPS).
- Broken Authentication: Implementing weak authentication mechanisms that allow attackers to gain unauthorized access to the API.
To mitigate these vulnerabilities, API developers must use best practices such as input