FULL_STACK_DEVELOPER_2026_COMPLETE - Phase 05 API Design Decisions and Anti-Patterns
API Design Decisions and Anti-Patterns Professional contract choices without premature enterprise complexity
HTTP is the contract between independent programs.
REQUEST HTTP Client TaskFlow API
PowerShell / browser / later Next.js NestJS + Fastify RESPONSE
method + target + headers + optional body
status + headers + optional body
Figure - HTTP request/response exchange. Phase 05 studies the protocol before Phase 06 introduces a browser cross-origin call.
FULL_STACK_DEVELOPER_2026_COMPLETE - Phase 05 API Design Decisions and Anti-Patterns
API design decisions that age well Decision Prefer Avoid
Resource naming Plural nouns such as /todos Verb-heavy routes such as /getTodos
Representation Stable public shape Blindly expose every internal object
Anti-pattern: controller as the entire application The controller should not gradually accumulate arrays, database queries, permission rules and business workflows. Phase 05 keeps the in-memory array in TodosService so that when persistence changes later, the HTTP boundary remains conceptually stable.
Anti-pattern: status code as decoration If a client must inspect { success: false } to discover that a request failed while the HTTP status is 200, intermediaries, monitoring tools and generic client behavior lose useful protocol information. Use HTTP semantics rather than hiding them inside JSON.
Anti-pattern: design from screens instead of domain resources A UI might have buttons named Add, Finish, Archive, Restore and Delete. If every button becomes an endpoint name, the API becomes tightly coupled to one interface. Start from the resource and its state transitions, then introduce explicit action endpoints only when the domain operation itself deserves an action concept.
Anti-pattern: pretending Phase 05 input handling is production validation The manual title check in POST /todos is intentionally minimal. It does not give reusable schemas, transformation, field-specific validation or consistent DTO behavior. Later phases introduce a real validation boundary. A professional course should label temporary scaffolding honestly.
API contract review checklist ● Is the resource name meaningful without seeing the frontend? ● Does the method match the intended semantics? ● Can a client predict common success and failure statuses? ● Is the response shape stable and intentional? ● Is resource identity in the correct part of the URL? ● Are query parameters used for selection/filter/sort rather than hidden actions? ● Is the endpoint independently testable?
FULL_STACK_DEVELOPER_2026_COMPLETE - Phase 05 API Design Decisions and Anti-Patterns
● If the UI disappeared tomorrow, would the API still make sense?
We still do not add repository interfaces, shared API packages or OpenAPI generators. The learner first needs a real contract worth abstracting. Later phases can introduce tooling when a concrete maintenance problem appears.
Official source notes Primary protocol reference: RFC 9110 - HTTP Semantics (RFC Editor). Supplemental developer reference: MDN HTTP Reference and HTTP Request Methods. Nest-specific routing and status behavior reference: NestJS Controllers documentation.
This phase teaches HTTP semantics independent of a specific transport version. HTTP/2 and HTTP/3 change framing and transport details, while request methods, target resources, headers, status codes and representation semantics remain the important application-level concepts for this course.
Authentication answers who the request represents. Treating decoded or client-supplied identity as trusted is a security boundary failure.
Restate the goal of “API Design Decisions and Anti Patterns” as one observable behavior. Write the success signal before touching code.
Trace the boundary map: credentials/session → token → verification → trusted identity → protected operation. Mark the one boundary this lesson changes.
Inspect the current repository state and record the exact files, route, table, or runtime involved. Avoid creating an abstraction before you can name the existing owner.
Implement the smallest vertical slice. Add one coherent change, run the narrowest verification command, and read the output before continuing.
Connect the slice to TaskFlow’s phase artifact: A written TaskFlow API contract for tasks with request/response examples and deliberate error semantics.. Verify behavior from the outside as a user or API client would.
Create one controlled failure that is safe to reproduce. Predict the symptom first, capture evidence, locate the earliest broken boundary, then fix only that cause.
Close the reference and rebuild or explain the core change from memory. Record what you would monitor or test before trusting the same change in production.
const token = readBearerToken(request);
const claims = await verifier.verify(token);
request.user = {
id: claims.sub,
email: claims.email,
};Do not copy this as a finished answer. Predict what each boundary does, type the smallest useful slice, run it, then compare the result with your prediction.
Inspect whether a token exists, whether it is expired, which issuer/audience signed it, and what the API verifier expects.
Trust only verified server claims; never repair identity by accepting a client-sent user id.
Without copying the final source, create a second small scenario that applies “API Design Decisions and Anti Patterns” to a different TaskFlow resource or input. Write the acceptance criteria first, implement it, and provide the evidence that each criterion is satisfied.
Design collection and item URIs and justify GET/POST/PATCH/DELETE choices.
Use the smallest change that demonstrates this lesson. Stop after it works and capture evidence.Confusing authentication failures with authorization failures
Predict the symptom before causing the failure. Then locate the earliest boundary where reality diverges from expectation.Why does this responsibility live here, what input does it trust, what output proves success, and what would go wrong if another layer owned it?
If your explanation is vague, repeat the boundary trace before moving on.Close the reference. Reproduce the core idea from memory or explain the exact request/data flow aloud. Then check your diff or notes for accidental shortcuts that bypass validation, authorization, error handling, or verification earned in earlier phases.