Application Programming Interface(API)

In plain language

An API is a controlled doorway into a system. It specifies which requests are allowed, what information they require, and what response the requester can expect. An API is not synonymous with REST: REST is one architectural style used for some web APIs.

Why it matters to a business

• Lets systems share capabilities without exposing their internal implementation
• Creates a stable boundary for integrations, applications, and automation
• Makes access, validation, versioning, and usage limits explicit

How it works

1. 1A provider publishes operations and data contracts.
2. 2A consumer authenticates when required and sends a request in the documented form.
3. 3The provider validates the request, applies business rules, and returns a result or defined error.
4. 4Production consumers handle timeouts, rate limits, version changes, and partial failure.

Common use cases

• Connecting a customer portal to an order system
• Retrieving CRM records for an internal dashboard
• Creating payments through a payment provider
• Exposing product capabilities to approved partners

Important implementation decisions

• Resource and operation design
• Authentication and authorization boundaries
• Versioning and compatibility policy
• Rate limits, pagination, errors, and observability

Common mistakes and misconceptions

• Assuming every API is RESTful
• Treating API availability as proof that an integration is simple
• Exposing database structures instead of stable business contracts

Limitations and trade-offs

Authoritative references

• IETF HTTP Semantics (RFC 9110)