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Advanced Topic 38 of 50 Software Engineering

API Design

Crafting clear stable interfaces between systems.

How it works

API design is the craft of defining how software components or services expose functionality to others. Good APIs are consistent, predictable, hard to misuse and well documented, with clear naming, stable contracts, meaningful error responses, pagination, filtering and versioning strategies. Security considerations include authentication, authorization, rate limiting and input validation. Specifications such as OpenAPI describe REST interfaces, and schemas enable generated clients and documentation.

Step-by-step walkthrough

  1. Start from what API consumers need.
  2. Name resources clearly and use consistent verbs.
  3. Keep the contract stable and version breaking changes.
  4. Return useful errors and document with examples.
  5. A good API is hard to misuse.

Where it is used

Public web APIs, internal service interfaces, library interfaces and SDKs all require design effort, because once published, changes are costly for consumers.

Common pitfall

Breaking changes without versioning destroy client trust. Leaking internal data models, inconsistent naming, vague errors and missing idempotency for retries make APIs painful. Overly chatty or overly large responses hurt performance. Design from the consumer's perspective, write examples first, deprecate gradually and test the contract.

Where it fits in the course

API Design is topic 38 of 50 in Software Engineering, rated Advanced. It follows CQRS and Event Sourcing. The next topic is REST.

Practice and explore

How to study this topic

  1. Read the explanation above and restate the definition in your own words.
  2. Open the interactive lesson and answer its mini quiz.
  3. Read the common pitfall, then write a short example that avoids it.
  4. Check your understanding in the Software Engineering quiz, and revisit the topic if you miss a question.

Frequently asked questions

What is API Design?
Crafting clear stable interfaces between systems. It belongs to Software Engineering and is an advanced-level topic.
Where do people use API Design?
Public web APIs, internal service interfaces, library interfaces and SDKs all require design effort, because once published, changes are costly for consumers.
What is the most common mistake with API Design?
Breaking changes without versioning destroy client trust.
What should I learn before this topic?
Start with CQRS and Event Sourcing, the topic just before it in Software Engineering.
How can I practice it?
Answer the mini quiz in the interactive lesson, then take the Software Engineering quiz.
Is API Design hard to learn?
It is an Advanced topic. Expect to read the explanation more than once and to connect it with earlier topics. Working through a small example by hand helps most.
How long does it take to learn API Design?
Most learners can read the explanation and finish the interactive lesson in under an hour. Fluency comes from applying the idea, so plan a few short practice sessions with the quiz.
Which topics are related to API Design?
CQRS and Event Sourcing, REST, Event-Driven Architecture are closely connected. The full list is in the related topics section of this page.
What should I study after API Design?
Continue with REST, the next topic in Software Engineering.

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