Definition
API stands for Application Programming Interface. It is a set of rules and protocols that allow different software applications to communicate with each other. APIs define how requests and responses are structured, enabling developers to connect systems, services, or devices without needing to understand their internal workings.
APIs are commonly used to integrate third-party services, connect frontends to backends, and enable automation. For example, an e-commerce site may use an API to process payments, retrieve product data, or send shipping updates.
Advanced
At an advanced level, APIs can be designed using different architectures. REST APIs use standard HTTP methods such as GET, POST, PUT, and DELETE. GraphQL provides a flexible query language for fetching exactly the data needed. SOAP is a protocol-driven model often used in enterprise environments.
Modern APIs use authentication and authorisation standards such as OAuth 2.0, API keys, or JWTs. They may include rate limiting, caching, and monitoring to improve performance and security. APIs are also central to microservices and serverless architectures.
Why it matters
- Enables seamless integration between applications and services.
- Reduces development time by reusing existing functionality.
- Supports scalability and modular system design.
- Powers digital experiences across mobile, web, and connected devices.
Use cases
- Processing payments through a payment gateway API.
- Connecting mobile apps to back-end servers.
- Automating workflows between CRM, ERP, and marketing tools.
- Delivering data from headless CMS platforms to websites and apps.
Metrics
- API response time and latency under load.
- Uptime and reliability of API endpoints.
- Error rates in requests and responses.
- Usage volume and rate limit performance.
Issues
- Security vulnerabilities if APIs are not properly authenticated.
- Downtime or rate limits affecting dependent services.
- Poor documentation leading to integration challenges.
- Versioning and backward compatibility issues for long-term use.
Example
A travel booking website uses multiple APIs to deliver its services. One API retrieves flight data, another handles payments, and a third manages customer reviews. By integrating these services, the company provides a seamless user experience without building every feature in-house.