What is a Web Service? (API)

Almost every modern app — whether it's a banking app, a weather app, or an e-commerce site — gets its data by talking to a web service. This guide explains what web services are, what an API is, and how REST (the most popular style) actually works. No jargon — just plain English and real examples.

1. What is a Web Service?

A web service is a way for two software systems to talk to each other over the internet. One system sends a request, the other processes it and sends back a response.

Web services are used everywhere:

• A weather app fetches today's temperature from a weather web service.
• A payment page sends your card details to a payment web service (like Stripe or Razorpay).
• An OutSystems app calls a web service to get a list of countries to populate a dropdown.
• A logistics app calls a courier's web service to create a shipment and get a tracking number.

2. What is an API?

API stands for Application Programming Interface. It is the contract — the agreed set of rules — that defines how two systems will talk to each other.

The API defines:

• What you can ask for (the endpoints — the URLs)
• How to ask for it (the HTTP method, the format)
• What authentication you need (key, password, token)
• What you will get back (the response format, usually JSON)

3. Types of Web Services

Over the years, different styles of web services have been invented. The three most common are:

SOAP is the oldest. It uses XML (lots of angle brackets — very verbose) and has very strict rules. It's still widely used in banking and enterprise systems but is considered complex.

GraphQL is a newer style where you ask for exactly the fields you want. Very flexible, but more complex to set up.

REST is the most popular style today. It's simple, uses the standard HTTP protocol you already know from browsing the web, and returns data in JSON — which is easy to read and work with. This guide focuses on REST.

4. RESTful APIs — The Most Important One

A RESTful API uses the same protocol your browser uses to load websites — HTTP. This makes it simple and universal. Any language (PHP, Java, Python, JavaScript) and any platform (OutSystems, mobile app, web app) can call a REST API.

The base URL

Every REST API has a base URL — the root address of the API:

https://labs.lowcademy.com/apis/

Endpoints

An endpoint is a specific path added to the base URL. Each endpoint represents a resource — something you can get or act on:

https://labs.lowcademy.com/apis/countries.php   ← list of countries
https://labs.lowcademy.com/apis/users.php       ← list of users
https://labs.lowcademy.com/apis/currency.php    ← currency converter

Key principles of REST

• Uses standard HTTP verbs — GET, POST, PUT, DELETE to say what you want to do.
• Returns JSON — data comes back in a clean, readable format.
• Each URL is a resource — /users = users, /products = products.
• Stateless — each request is independent. The server doesn't remember you from the last call.

5. HTTP Methods

The HTTP method tells the server what action you want to perform. Think of it as the verb of the request.

6. Anatomy of an API Request & Response

Every API call has two parts: what you send (the request) and what you get back (the response).

The Request

The Response

7. JSON — How Data Travels

JSON (JavaScript Object Notation) is the standard format for sending and receiving data in REST APIs. It's lightweight and easy to read. You'll see it everywhere.

Basic JSON structure

{
  "success": true,
  "name": "India",
  "code": "IN",
  "population": 1400000000
}

JSON supports these data types: strings (text in quotes), numbers, booleans (true/false), arrays (lists), and objects (key-value pairs). An API response is almost always a JSON object at the top level.

JSON with an array of objects

{
  "success": true,
  "count": 3,
  "data": [
    { "id": 1, "name": "Ankit", "role": "Admin" },
    { "id": 2, "name": "Priya", "role": "User" },
    { "id": 3, "name": "Ravi",  "role": "User" }
  ]
}

8. Real Examples

Example 1 — GET with no parameters

Get a greeting from the Hello World API. No auth, no body needed.

Request

GET https://labs.lowcademy.com/apis/hello.php

Response

{
  "success": true,
  "message": "Hello, World!",
  "timestamp": "2026-07-12 10:30:00"
}

Example 2 — GET with a query parameter

Pass a name in the URL to personalise the response.

Request

GET https://labs.lowcademy.com/apis/hello.php?name=Ankit

Response

{
  "success": true,
  "message": "Hello, Ankit!",
  "timestamp": "2026-07-12 10:30:01"
}

Example 3 — GET with filter parameter

Fetch countries filtered by region.

Request

GET https://labs.lowcademy.com/apis/countries.php?region=Asia

Response

{
  "success": true,
  "count": 35,
  "data": [
    { "code": "IN", "name": "India",  "region": "Asia" },
    { "code": "JP", "name": "Japan",  "region": "Asia" }
  ]
}

Example 4 — GET with Basic Auth

Some APIs protect their endpoints with a username and password. The credentials are sent in the request header.

Request (cURL)

curl -u admin:1234 https://labs.lowcademy.com/apis/me.php

Response

{
  "success": true,
  "profile": {
    "id": 1,
    "username": "admin",
    "name": "Admin User",
    "role": "Administrator"
  }
}

9. API Authentication

Most APIs require you to prove who you are before they give you data. This is called authentication. Common methods: