Glossary · web
API
Definition
An API (Application Programming Interface) is a contract that lets two software systems talk in a structured way. It exposes endpoints to fetch data, send data, and trigger actions; REST and GraphQL are the two most common models. Most modern web features are powered by API calls.
Detailed explanation
An API is a 'contract' in software: one system declares upfront which data it will provide in which format and which actions it accepts. The client (frontend, mobile app, another service) sends requests following these rules, and the API returns responses.
REST API is the dominant approach in 2026 — it manages resources over HTTP with GET/POST/PUT/DELETE. GraphQL is more flexible (client picks fields it needs), efficient for complex UIs. tRPC gives end-to-end type safety in TypeScript projects.
API usage: payment integration (Stripe, iyzico), maps (Google Maps), AI (OpenAI, Anthropic), e-invoice (Foriba, Paraşüt), marketplace (Trendyol, Hepsiburada). 95%+ of modern web/mobile apps consume external APIs.
Use cases
→Mobile app talking to its backend
→3rd-party service integration (payment, shipping, AI)
→Microservices talking to each other
→Webhook event notifications
→Public API for partner ecosystem
Pros
- +Modular architecture — components evolve independently
- +Multi-platform — same backend serves web + iOS + Android
- +Reusability across surfaces
- +Versioning enables backward-compatible updates
Cons
- −Network latency (50-500ms per call)
- −Rate limiting + auth complexity
- −Versioning + backward compat work
- −Poorly designed APIs become integration nightmares
Related terms
Related services
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