Types of APIs

Not all APIs are built the same way. There are three main styles you'll encounter in the industry: REST, SOAP, and GraphQL. As a QA engineer, you'll spend 90% of your time testing REST APIs. But you need to know the others because they show up in interviews and legacy projects.

REST — The Industry Standard

REST (Representational State Transfer) is how most modern APIs work. It uses standard HTTP methods (GET, POST, PUT, DELETE), communicates in JSON format, and every resource has a unique URL. Simple, lightweight, and easy to test.

# REST API example — get a user
curl https://api.example.com/users/42

# Response: JSON
{
  "id": 42,
  "name": "Priya Sharma",
  "email": "priya@example.com"
}

SOAP — The Enterprise Veteran

SOAP (Simple Object Access Protocol) is older, heavier, and uses XML instead of JSON. You'll find it in banking, insurance, and government systems — anywhere that was built 10-15 years ago. It's strict, verbose, but very secure. Testing it is painful because XML is harder to read than JSON.

<!-- SOAP Request — same "get user" operation -->
<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
  <soap:Body>
    <GetUser>
      <UserId>42</UserId>
    </GetUser>
  </soap:Body>
</soap:Envelope>

GraphQL — The Modern Challenger

GraphQL was created by Facebook. Instead of multiple endpoints, there's one endpoint. You tell it exactly what fields you want, and it returns only those fields. No over-fetching, no under-fetching. Great for mobile apps where bandwidth matters.

# GraphQL — ask for exactly what you need
query {
  user(id: 42) {
    name
    email
  }
}

# Response: only what you asked for
{
  "data": {
    "user": {
      "name": "Priya Sharma",
      "email": "priya@example.com"
    }
  }
}

Side-by-Side Comparison