API Documentation and OpenAPI
Create documentation that developers can actually use and machines can validate.
What Good API Documentation Contains
Good documentation explains authentication, base URLs, endpoints, parameters, request examples, response examples, errors, pagination, rate limits, webhooks, versioning, and common workflows.
Documentation should answer practical questions: How do I authenticate? How do I create a resource? What happens when validation fails? How do I paginate? How do I retry safely?
Examples are often more useful than prose alone.
- Document behavior, not only endpoint names.
- Include realistic examples.
- Document errors and authentication as first-class concepts.
OpenAPI Paths, Operations and Schemas
An OpenAPI document normally contains metadata, servers, paths, operations, parameters, request bodies, responses, reusable schemas, security schemes, and examples.
Schemas can define reusable resource models. Operations describe the HTTP method and expected behavior.
The specification can become the source for interactive documentation, client generation, mock servers, validation middleware, and automated compatibility checks.
components:
schemas:
User:
type: object
required:
- id
- name
properties:
id:
type: string
name:
type: string
email:
type: string
format: emailDesign-First vs Code-First
API Design Approaches
In code-first development, implementation is created first and documentation is generated from code annotations or runtime metadata.
In design-first development, the API contract is designed before implementation. Teams can review resource models, status codes, schemas, and security requirements before writing server code.
Design-first is especially useful for teams with multiple consumers because frontend and backend developers can work against a shared contract.
Implementation → contractContract → implementation