What is an API?
You can think of an API as a URL which connects two different systems and acts as a broker which transfers the data in different formats. A broker can do logic in the middle and transform the data in a way the source or target system expects.
An API (Application Programming Interface) is a set of rules and tools that allows different software applications to communicate with each other. APIs define the types of requests that can be made, how to make them, the data formats to use, and the conventions for error responses.
Why APIs matter
APIs enable systems to share data and functionality without exposing implementation details. They are essential in modern software because they enable modular design, integration between services, and automation of workflows across different platforms.
Common types of APIs
- REST (Representational State Transfer) — REST API is a type of API which is built on top of HTTP protocol. It's a framework which defines HTTP Methods, request and response types, examples, schemas etc. It typically uses JSON but can use other data formats as well
- SOAP (Simple Object Access Protocol) — SOAP is a protocol which uses strict XML type data, a user has to adher SOAP envelopes to communicate. It's more robust and secure but consumes more network bandwidth and strict standards
- GraphQL — A query language and runtime for requesting data where the client specifies the exact shape of the response. This helps reduce over-fetching and under-fetching of data.
- gRPC — Uses HTTP/2 with protobuf for efficient binary serialization, suitable for low-latency microservices and high-performance internal APIs.
- Webhooks — Simple HTTP callbacks used to notify systems of events — these are push-based rather than request-response.
Design & security considerations
APIs must be designed keeping performance, security, and stability in mind. Considerations include authentication (API keys, OAuth, JWT), rate-limiting, versioning, documentation, and monitoring. Ensure sensitive data is transmitted securely and follow least-privilege principles.
REST API Fundamentals and best practices
This topic is covered in depth on its own page: REST API Fundamentals and best practices. The dedicated article includes resource naming guidance, HTTP methods, request/response schemas, and recommended response codes.
How to choose the right API type
Consider the use case: REST is ideal for general-purpose web APIs, GraphQL works well when clients need flexible queries, gRPC is best for performant internal services, and SOAP remains relevant in legacy enterprise integrations where strict contracts are required.
Conclusion
Understanding what an API is and the common types will help you choose better integration patterns and design more robust services. For integration projects, start with clearly defined API contracts, secure communication, and proper monitoring.