API
An API is primarily focused on enabling communication between a web service and a client application. It typically has narrower scopes and may offer functions or methods as clear-cut entry points.
Web Service
A web service, on the other hand, is more expansive, enabling interaction not just with clients, but also with other softwares, resulting in a more comprehensive service-oriented architecture.
1. What is an API?
API (Application Programming Interface) is a general concept. An API is a set of rules and definitions that allows one software component to communicate with another.
Key points:
- Can be local or remote
- Can use any protocol or method
- Can expose functions, classes, or endpoints
- Not necessarily over the internet
Examples:
- Java API (
List,Map) - .NET API (
System.IO) - Browser APIs (
localStorage,Geolocation) - REST API between frontend and backend
All web services are APIs, but not all APIs are web services.
2. What is a Web Service?
A Web Service is a specific type of API that:
- Communicates over the web
- Uses standard web protocols
- Is designed for machine-to-machine communication
Key points:
- Always network-based
- Uses HTTP/HTTPS
- Data format is standardized (XML, JSON)
- Platform and language independent
Examples:
- RESTful services
- SOAP services
- GraphQL services
3. Key Differences (Side-by-Side)
| Aspect | API | Web Service |
|---|---|---|
| Scope | Broad concept | Subset of API |
| Network required | Not always | Always |
| Protocols | Any (TCP, HTTP, in-process) | HTTP/HTTPS |
| Data format | Any | XML / JSON |
| Platform independent | Not required | Yes |
| Example | Java API, OS API | REST, SOAP |
4. Types of Web Services
Common web service types:
- SOAP – XML-based, strict standards
- REST – Lightweight, HTTP-based, most popular
- GraphQL – Client-driven queries
- gRPC – Binary, high-performance
5. Simple Real-World Analogy
- API → A contract/menu that defines what you can ask for
- Web Service → A waiter delivering your order over the internet
Menu inside a restaurant = API
Online food delivery = Web Service
6. One-Line Interview Answer
An API is a general interface for software communication, while a web service is an API that communicates over the web using standard protocols like HTTP.
