What is API integration?
An API (Application Programming Interface) is an interface that allows two applications to communicate and exchange data. API integration means connecting business systems so they can automatically share information without human intervention.
Think of it as a universal language for applications. When the HR system adds a new employee, it automatically calls Active Directory via API: "Create an account for John Smith with the Manager role." Active Directory replies: "Done, account created, permissions assigned." Everything runs in the background, in real time.
API types: REST vs. GraphQL vs. SOAP
REST API (Representational State Transfer)
REST API is today's most popular API type. It uses standard HTTP methods (GET, POST, PUT, DELETE) and transfers data in JSON or XML format.
Advantages of REST API:
- Simple to understand and implement
- Broad support across all programming languages
- Fast and efficient (low overhead)
- Stateless architecture — each request is independent
- Caching for better performance
Disadvantages of REST API:
- Over-fetching or under-fetching of data
- Multiple requests for complex data
- Weaker schema validation than GraphQL
GraphQL
GraphQL is a query language for APIs developed by Facebook. Instead of fixed endpoints, the client specifies exactly what data it wants to retrieve.
Advantages of GraphQL:
- Exactly what you need — no over-fetching
- Single request for complex data
- Strong type safety and schema validation
- Excellent developer tools (GraphQL Playground)
Disadvantages of GraphQL:
- More complex server-side implementation
- Worse caching than REST
- Higher learning curve
SOAP (Simple Object Access Protocol)
SOAP is an older but still widely used protocol, particularly in legacy enterprise systems and the financial sector. It uses XML for data transfer and has a strict structure.
Advantages of SOAP:
- Very strict schema validation (WSDL)
- Built-in security (WS-Security)
- Transactional reliability (ACID)
- Standardised error handling
Disadvantages of SOAP:
- More complex and "heavier" than REST
- XML is verbose (larger payloads)
- Less flexibility
Business systems API integration examples
1. ERP Integration
Connecting accounting systems such as SAP, Helios, Money S3, Pohoda with other applications.
Scenarios:
- E-commerce platform automatically creates invoices in the ERP system
- Current stock levels synchronise with the website in real time
- Bank payments are matched with invoices in accounting
- Project system costs are pulled into ERP for reporting
2. CRM and Marketing Automation
Integrating Salesforce, Microsoft Dynamics, HubSpot with email platforms, analytics dashboards and e-commerce.
Scenarios:
- A new lead from a website form automatically creates a record in CRM
- Sales rep closes a deal in CRM → automatic onboarding email
- Customer website behaviour is stored in CRM for better personalisation
- Email marketing platform synchronises subscriber status with CRM
3. HR and Active Directory
Automating employee management and permissions.
Scenarios:
- New employee in HR → automatic account creation in AD
- Position change → automatic permissions update
- Employee departure → instant deactivation of all access
- Organisational structure synchronisation across all systems
4. Payment Gateways and Fintech
Integration of payment systems, banking APIs and fintech services.
Scenarios:
- Online payments via Stripe, PayPal, GoPay
- Automatic bank transaction reconciliation
- Payment card tokenisation (PCI DSS compliance)
- Real-time exchange rates for international payments
API integration security
API integrations often carry sensitive business data, so cybersecurity is critical. All our API integrations meet NIS2 compliance standards.
Key security practices:
1. Authentication and Authorisation
- OAuth 2.0 — modern authorisation standard
- JWT tokens — secure identity transport
- API keys — simple but less secure (internal APIs only)
- Mutual TLS (mTLS) — bidirectional certificate verification
2. Encryption
- HTTPS/TLS — always encrypted communication (never plain HTTP)
- Sensitive data encryption — passwords, payment data, personal information
- Certificate pinning — protection against man-in-the-middle attacks
3. Rate Limiting and Throttling
- Limit on requests per minute/hour
- Protection against DDoS attacks
- Fair usage policy for all clients
4. Monitoring and Logging
- Audit logs of all API calls
- Alerts on suspicious activity
- Application Insights / Azure Monitor
- GDPR-compliant logging (no sensitive data)
API integration architecture
Point-to-Point Integration
Direct connection between two systems — the simplest option for small projects.
Advantages: Fast implementation, low cost
Disadvantages: Doesn't scale — with 10 systems you need 45 integrations
Hub & Spoke (ESB)
A central integration hub through which all communication flows.
Advantages: Centralised management, process orchestration, easier monitoring
Disadvantages: Single point of failure, higher complexity
Microservices & Event-Driven
Modern event-driven architecture using Azure Service Bus, RabbitMQ or Kafka.
Advantages: High scalability, resilience, asynchronous communication
Disadvantages: More complex development and maintenance
Implementing API integration: Step by step
Step 1: Requirements analysis
- Which systems do you want to connect?
- What data should be synchronised?
- How frequently? (real time / hourly / daily)
- Bidirectional or unidirectional communication?
Step 2: API discovery
- Does the system have a REST API? GraphQL? SOAP?
- What are the rate limits and restrictions?
- How does authentication work? (OAuth, API key, Basic Auth)
- Is there documentation? (OpenAPI / Swagger)
Step 3: Integration design
- Design the architecture (point-to-point / hub / event-driven)
- Define data mapping (how fields from system A map to system B)
- Plan error handling and retry logic
- Design monitoring and alerting
Step 4: Implementation
- Develop API clients and connectors
- Implement transformation logic
- Configure authentication and security
- Unit tests and integration tests
Step 5: Testing
- Testing with test data
- Load testing (can the system handle expected volumes?)
- Security testing (penetration tests)
- User acceptance testing (UAT)
Step 6: Deployment & Monitoring
- Phased rollout (pilot first, then production)
- Set up monitoring (Application Insights)
- Alerting on errors or downtime
- Documentation for the operations team
Costs and ROI
Small integration
150–500K CZK
2–3 systems, simple logic, standard REST API
Medium integration
500K – 2M CZK
4–6 systems, complex transformations, ESB architecture
Enterprise integration
2M+ CZK
10+ systems, event-driven, high availability, 24/7 support
Return on investment (ROI): Typically 12–24 months. Savings come from eliminating manual work, reducing errors and faster processes. Companies with strong API integration save up to 40% of IT operational costs.
Conclusion
API integration is the foundation of a modern enterprise IT infrastructure. A well-implemented integration connects your systems, automates data flows and saves hundreds of hours of manual work per month.
At Optimaly we deliver API integrations for large enterprise clients such as CLA Czech Republic and Eurowag. We specialise in the .NET / Azure stack, have an in-house development team and capacity for projects of 10M+ CZK. All our integrations meet NIS2 compliance and are ready for the 2025 regulatory environment.
Want to connect ERP, CRM or HR? We offer a free integration consultation and custom enterprise integration.