Video lesson: Designing APIs Around Explicit Semantics

Lesson promise

By the end, the learner should be able to explain the core model for designing apis around explicit semantics, apply it to a concrete input, and identify when its usual shortcut or guarantee stops applying. This is a recording brief; publish it as a playable lesson after the narration and visual sequence have been produced and reviewed.

Narration draft

An API contract defines the meaning of operations, inputs, outputs, errors, and side effects. A good contract lets clients reason about retries and compatibility without depending on undocumented server behavior. HTTP methods communicate broad intent, while the application contract defines the resource-specific rules.

A PUT that replaces a resource can be retried safely when the same request produces the same target state. A POST that creates a payment may create duplicates unless the server recognizes an idempotency key. A response should distinguish validation failures, authorization failures, and transient server problems.

Backward compatibility includes behavior as well as field names: changing default ordering or error semantics can break clients. Adding an optional field is often safer than changing a required one, but strict client decoders may still reject it. Version only when compatibility policy and migration need justify it.

Visual sequence

1. Put the input and assumptions on screen. Ask the learner to predict the next state before revealing it.
2. Animate the representation and show the operation one transition at a time.
3. Pause at the boundary case in the companion article and compare the result with the invariant.
4. End with the exercise prompt: An endpoint creates an invoice but the client times out before receiving the response. Specify a request and storage design that lets the client retry without creating a second invoice.

Companion material

Use the article, trace, and interactive concept flow as the learner’s written and visual references. The video remains planned until an actual playable media URL and reviewed transcript are available.