API Design Principles
When your frontend needs data from your backend, it communicates through an API. A well-designed API feels intuitive — developers can guess how it works. A poorly designed API causes confusion and bugs. Understanding basic design principles helps you build better systems and communicate effectively with AI.
REST Basics
Most web APIs follow REST (Representational State Transfer) conventions. REST organizes your API around resources — the things your application manages — and uses HTTP methods to describe actions on those resources.
Resources are nouns: /users, /todos, /stocks, /orders
HTTP methods are verbs:
GET— Retrieve dataPOST— Create new dataPUT— Update existing data (replace entirely)PATCH— Update existing data (partial changes)DELETE— Remove data
Combining these gives you predictable endpoints:
GET /todos → List all todos
POST /todos → Create a new todo
GET /todos/123 → Get todo with ID 123
PUT /todos/123 → Update todo 123
DELETE /todos/123 → Delete todo 123
Consistency Matters
The most important principle is consistency. If /users/123 gets a specific user, then /todos/456 should get a specific todo. If creating a user returns the created object, creating a todo should too.
Inconsistent APIs force developers to constantly check documentation. Consistent APIs let them work from intuition.
Using AI for API Design
AI excels at generating API designs when you describe your requirements clearly. Here's an effective prompt pattern:
"Design a REST API for a simple todo app with these features:
- List all todos
- Create a new todo
- Mark a todo as complete
- Delete a todo
Show me the endpoints, HTTP methods, request bodies, and responses."
AI will generate a complete, consistent design you can review and refine.
Response Design
Good APIs return predictable response structures. Include the data requested, use consistent field names, and return appropriate status codes. When errors occur, return helpful messages that explain what went wrong.
Start Simple
For your first projects, keep APIs minimal. You can always add endpoints later. A simple, consistent API beats a complex, inconsistent one every time.