REST API Engineering: HTTP Verbs, Idempotency & CORS Security
Representational State Transfer (REST) is the prevailing architectural standard for web APIs, microservices, and mobile client-server communication. Built on the core RFC 9110 HTTP specification, RESTful systems use standardized verbs, stateless headers, and resource-oriented URIs to manipulate data records.
1. HTTP Methods & Idempotency Matrix
| Method | Safe | Idempotent | Primary Purpose |
|---|---|---|---|
| GET | Yes | Yes | Retrieve resource representation without side effects |
| POST | No | No | Create a new resource or execute processing actions |
| PUT | No | Yes | Replace entire target resource or create at specified URI |
| PATCH | No | No | Apply partial delta modifications to an existing resource |
| DELETE | No | Yes | Remove target resource from the server collection |
2. Understanding CORS (Cross-Origin Resource Sharing)
Browsers enforce the Same-Origin Policy (SOP) by default, restricting scripts in one origin from requesting resources located on a different domain. When making client-side fetch() calls, the target server must return valid CORS headers:
- Access-Control-Allow-Origin: Declares which origins are authorized (e.g.
*orhttps://compare-value.com). - Access-Control-Allow-Methods: Permitted verbs (e.g.
GET, POST, OPTIONS, DELETE). - Access-Control-Allow-Headers: Authorized custom headers (e.g.
Content-Type, Authorization).
Frequently Asked Questions (FAQ)
Can I test any API endpoint from this browser client?
Yes, you can test any public API, mock service, or local development server (like localhost:3000 or localhost:8000). Note that external third-party APIs must have CORS (Cross-Origin Resource Sharing) enabled or allow browser fetch requests.
How are request authentication headers handled?
You can add custom Authorization headers, Bearer tokens, or API keys in the Headers tab. All credentials are kept strictly in your local browser memory and are dispatched directly to the target API endpoint without server logging.
Can I export my request to cURL or code snippets?
Yes. With a single click, you can generate ready-to-use cURL commands, JavaScript Fetch API snippets, and Python Requests scripts populated with your custom headers, parameters, and JSON payloads.
What HTTP methods and status codes are supported?
The playground supports all standard HTTP verbs (GET, POST, PUT, PATCH, DELETE, HEAD) and decodes standard 1xx, 2xx, 3xx, 4xx, and 5xx response statuses with detailed duration and payload size metrics.