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🌐 RESTful API Design Guide

Designing RESTful APIs involves following principles that improve clarity, scalability, and developer experience. This guide outlines best practices, tips, and common pitfalls when designing robust and intuitive REST APIs.

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📦 Domain Model Driven Paths

Base your endpoint structure on domain entities and relationships rather than technical implementation.

/users/{userId}/orders
/products/{productId}/reviews
/teams/{teamId}/members

Avoid verbs in the path — actions should be implied by the HTTP method.

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🔧 Use Proper HTTP Methods

Stick to the semantics of HTTP:

Method	Use Case
GET	Retrieve resource
POST	Create a new resource
PUT	Replace an entire resource
PATCH	Partially update a resource
DELETE	Remove a resource

GET    /users           -> list users
POST   /users           -> create new user
GET    /users/42        -> get user with ID 42
PUT    /users/42        -> replace user 42
PATCH  /users/42        -> update user 42 partially
DELETE /users/42        -> delete user 42

💡 Tip: PATCH is useful but requires careful idempotent implementation. Consider using PUT for simplicity when applicable.

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🔁 Implement Idempotency

Idempotent APIs produce the same result regardless of how many times the operation is repeated.

• GET, PUT, DELETE, and PATCH should be idempotent.
• For POST, use idempotency keys or client-generated IDs.

POST /payments
Headers: Idempotency-Key: abc123

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🧾 Choose Consistent HTTP Status Codes

Use a consistent subset of HTTP status codes for clarity:

Code	Meaning
200	OK
201	Created
204	No Content (e.g., after DELETE)
400	Bad Request
401	Unauthorized
403	Forbidden
404	Not Found
409	Conflict
422	Unprocessable Entity (e.g., validation)
500	Internal Server Error

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🔢 API Versioning

Avoid breaking clients by versioning your API:

• URI versioning: most common

GET /v1/users

• Header-based or content negotiation is more advanced and flexible but harder to adopt universally.

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📖 Semantic & Intuitive Paths

Paths should be descriptive, consistent, and pluralized.

❌ Avoid:

/getAllUsers

✅ Prefer:

/users

Use nouns (resources), not verbs (actions).

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🧩 Batch Processing

Enable bulk actions using a consistent keyword and path suffix:

POST /orders/batch
PATCH /users/batch

Ensure partial failures return informative responses.

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🔍 Flexible Query Language

Support advanced querying capabilities using standard query params:

• Filtering:
  /users?role=admin

• Pagination:
  /users?limit=10&offset=20

• Sorting:
  /products?sort=-price

Tip: Use RSQL or OData-style query specs for consistency if the API becomes complex.

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🧪 Validation & Errors

• Validate input and return helpful error messages.
• Use a consistent error response format.

{
  "error": {
    "code": "INVALID_EMAIL",
    "message": "Email must be a valid format.",
    "field": "email"
  }
}
</codexample>

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## 🛡️ Security

- Use **HTTPS** only.
- Apply **rate limiting** and **authentication** (OAuth2, API keys).
- Avoid leaking sensitive data in error responses.
- Use **allowlists** to restrict access to IPs or clients.

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## 🔁 HATEOAS (Optional)

Hypermedia As The Engine Of Application State — not always required but good for discoverability:

{ "user": { "id": "42", "name": "Alice", "links": [ { "rel": "self", "href": "/users/42" }, { "rel": "orders", "href": "/users/42/orders" } ] } }

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## 📚 Example RESTful Resources

| Entity        | Endpoints                         |
|---------------|------------------------------------|
| Users         | `/users`, `/users/{id}`           |
| Orders        | `/orders`, `/orders/{id}`         |
| Products      | `/products`, `/products/{id}`     |
| Auth          | `/login`, `/logout`, `/register`  |
| Metrics       | `/health`, `/metrics`, `/status`  |

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## ✅ Final Checklist

- [x] Use nouns, not verbs in paths
- [x] Stick to proper HTTP methods
- [x] Apply consistent status codes
- [x] Enable query flexibility
- [x] Secure your API
- [x] Validate input and structure errors
- [x] Design with versioning in mind

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A well-designed RESTful API is **predictable**, **understandable**, and **future-proof**. Stick to the principles outlined here to improve maintainability and developer experience.

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