Types of APIs

You've likely worked with different APIs, but understanding when to choose each type can make or break your architecture decisions. Let's explore the four main API categories and when to use them in real-world scenarios.

Public APIs

Public APIs are open to any developer after basic registration. They're designed for widespread adoption and external integration.

Real-world scenario: Stripe's payment API handles complex PCI compliance while you focus on your product logic. After registering, you get sandbox access, clear documentation, and production endpoints. Instead of building payment infrastructure from scratch, you can process transactions with a few API calls.

// Stripe payment processing
const stripe = require('stripe')('sk_test_...');
const paymentIntent = await stripe.paymentIntents.create({
  amount: 2000,
  currency: 'usd',
  payment_method: 'pm_card_visa',
  confirm: true,
});

When to choose public APIs:

• You need specialized functionality that's expensive to build internally

• Time-to-market is critical

• You want to focus on core business logic rather than infrastructure

Private APIs

Private APIs connect internal systems and services within your organization's firewall.

Real-world scenario: A hospital's electronic health records (EHR) system uses private APIs to communicate with appointment scheduling software. When a doctor orders lab tests, the API automatically reserves equipment and notifies lab personnel, all while keeping patient data secure behind the firewall.

// Internal API call within hospital system
async function scheduleLabTest(patientId, testType) {
 
  const payload = {
    patient_id: patientId,
    test_type: testType,
    priority: 'normal'
  };
 
const response = await fetch('http://internal-scheduler.hospital.local/api/labs', {
 
    method: 'POST',
    headers: {
      'Content-Type': 'application/json',
      'Authorization': Bearer ${internalToken}
    },
    body: JSON.stringify(payload)
  });
 
  return response.json();
}

When to choose private APIs:

• Building a microservices architecture

• Connecting different teams' services

• Preparing for potential public release later

• Need strict security and access control

Partner APIs

Partner APIs sit between public and private, requiring formal agreements and specific business relationships.

Real-world scenario: PlayStation provides partner APIs to select game studios: these APIs access player profiles, achievements, and purchase systems. Sony carefully vets partners through contracts and technical compliance checks before granting access.

// Partner API with specific access controls
async function getPlayerData(playerId) {
 
  const headers = {
    'Authorization': Bearer ${partnerToken},
    'X-Partner-ID': partnerId,
    'Content-Type': 'application/json'
  };
 
  const response = await fetch(
    https://api.playstation.com/partner/v1/player/${playerId},
    { headers }
  );
 
  return response.json();
}

When to choose partner APIs:

• Building platform ecosystems with controlled access

• Managing supply chain integrations

• Creating reseller or distributor relationships

• Need quality control over who uses your API

Composite APIs

Composite APIs combine multiple operations into a single request, reducing complexity for API consumers.

Real-world scenario: A concert ticketing platform's composite API handles venue seating, availability checks, pricing, and payment processing in one call. Instead of making separate requests for each operation, developers send customer preferences and receive a complete booking response.

// Single composite API call handling multiple operations
const bookingResponse = await fetch('/api/composite/book-ticket', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/json',
    'Authorization': Bearer ${userToken}
  },
 
  body: JSON.stringify({
    event_id: 'concert-2024-01',
    seat_preference: 'orchestra',
    quantity: 2,
    payment_method: 'card_1234'
  })
});
 
// Response includes seat assignment, pricing, and payment confirmation
const result = await bookingResponse.json();

Behind the scenes, this composite API might execute:

1. Check seat availability

2. Calculate pricing with fees

3. Reserve seats temporarily

4. Process payment

5. Confirm booking

When to choose composite APIs:

• Simplifying complex workflows for external developers

• Reducing network requests and latency

• Building developer-friendly platforms

• Consolidating multiple internal services

When to use: Build composite APIs to streamline complex processes or provide simplified access to functionality that would otherwise require multiple separate API calls. They're particularly valuable when building developer-friendly platforms.

Choosing the Right API Type for Your Project

Consider these factors when selecting an API type:

Access Requirements:

• Team-only access → Private API

• Specific partners → Partner API

• Public developers → Public API

Security Needs: Private and partner APIs give you more control over access and data exposure. Public APIs require robust authentication, rate limiting, and input validation.

Stability Requirements: Public APIs need careful versioning and backward compatibility. Breaking changes can damage developer relationships and adoption.

Business Model:

• Public APIs might generate direct revenue or support product growth

• Partner APIs facilitate business relationships and ecosystem expansion

• Private APIs improve internal efficiency and integration