LEARN. PRACTICE. GROW.Concept and mechanism
An API lets applications cooperate through an observable contract. Consumers need to know resources, operations, required data, outcomes, and limits. REST describes an architectural style with interaction constraints; returning JSON over HTTP does not by itself establish all those properties. Business state may persist while each request carries enough context to be understood without depending on an implicit conversation stored between requests. Separate public representation from internal database organization. That separation allows implementation changes without requiring every consumer to know tables, queues, or internal names.
Guided application
In a fictional funds scenario, an API exposes reconciliation requests and their status. The contract should define identifiers, currency, precision, possible states, and errors. OpenAPI helps describe operations and schemas in a processable form; the OpenAPI document version is not the API’s product version. A declared component that is never referenced does not automatically enter an operation. Documentation also does not establish that implementation validates payloads or enforces authorization. During change, compare actual consumers with the contract: converting an amount from a number to text may require adaptation even if business meaning seems unchanged. Keep examples fictional and free of credentials or customer data.
A new schema only protects integration if it is connected to the operation and applied by intended controls.
Common pitfalls
JSON as proof of REST; schema as enforcement; OpenAPI version as product version.
Related topics: Requests and outcomes · Concurrency and retries · Authorization and boundaries
Make the contract actually used by consumers explicit.
Reference: OpenAPI Specification3.2.1 · HTTP semantics RFC9110; OpenAPI3.2.1; selected primary standards and provider contracts consulted2026-09-30