API Design A Complete Visual Guide

This book is for readers new to API design and systems engineers who need a structured way to turn business requirements into reliable, secure, and evolvable service contracts. It addresses a common concern: an interface may work in a simple demonstration yet fail in real projects because boundaries, HTTP behavior, errors, security, retries, compatibility, and operations were not designed together.

The guide builds systematically from core concepts to the intermediate and advanced techniques used in day-to-day systems engineering. Clear diagrams make boundaries, message flows, state transitions, trust zones, failure paths, and operational responsibilities easier to understand. Worked HTTP exchanges, OpenAPI and JSON Schema examples, commands, checklists, and troubleshooting scenarios show not only what to choose, but how to implement it, verify the result, and diagnose common failures.

Main learning topics:

• Turning business capabilities and domain language into stable service boundaries

• Choosing among resource-oriented HTTP, RPC, GraphQL, events, webhooks, streaming, and batch integration

• Designing resources, URIs, representations, methods, status codes, error contracts, pagination, bulk work, and concurrency control

• Creating executable contracts with OpenAPI and JSON Schema, then evolving them through compatible change, versioning, deprecation, and migration

• Applying threat modeling, authentication, machine identity, authorization, tenant isolation, data protection, and abuse controls

• Engineering resilience with deadlines, retries, cancellation, idempotency, sagas, recovery, long-running operations, and asynchronous communication

• Improving performance and operability with caching, traffic management, gateways, service meshes, testing, rollout controls, observability, SLOs, incident response, and governance

• Reviewing a production-ready B2B Order Management API from requirements through operations

After finishing the book, readers should be able to explain how an API works as a system contract, choose an appropriate interaction and consistency model, design and document a usable interface, protect it against common threats, verify behavior through tests and telemetry, plan safe change, and troubleshoot reliability or integration problems in practical project work.