HTTP Methods
Safe: no side effects on the server (read-only). Idempotent: repeating the request produces the same result as a single request — safe to retry after a network failure.
| Method |
Semantics |
Safe? |
Idempotent? |
Use For |
| GET |
Retrieve representation |
Yes |
Yes |
Reading data |
| POST |
Create subordinate resource |
No |
No |
Creating resources, non-idempotent operations |
| PUT |
Replace resource |
No |
Yes |
Full updates, idempotent creates |
| PATCH |
Partial update |
No |
No |
Partial updates |
| DELETE |
Remove resource |
No |
Yes |
Deleting resources |
| HEAD |
GET without body |
Yes |
Yes |
Checking existence, metadata |
| OPTIONS |
Describe capabilities |
Yes |
Yes |
CORS preflight, capability discovery |
Status Codes
Success
| Code |
Name |
Meaning |
| 200 |
OK |
Request succeeded (GET, PUT, PATCH with response body) |
| 201 |
Created |
Resource created (POST) |
| 202 |
Accepted |
Request accepted for async processing |
| 204 |
No Content |
Success with no response body (DELETE, PUT) |
Client Error
| Code |
Name |
Meaning |
| 400 |
Bad Request |
Invalid syntax or validation failure |
| 401 |
Unauthorized |
Authentication required |
| 403 |
Forbidden |
Authenticated but not authorized |
| 404 |
Not Found |
Resource doesn’t exist |
| 409 |
Conflict |
Request conflicts with current state (duplicate, version mismatch) |
| 422 |
Unprocessable Entity |
Syntax valid but semantic validation failed |
| 429 |
Too Many Requests |
Rate limit exceeded |
Server Error
| Code |
Name |
Meaning |
| 500 |
Internal Server Error |
Unexpected server failure |
| 502 |
Bad Gateway |
Upstream service failure |
| 503 |
Service Unavailable |
Temporary unavailability (overload, maintenance) |
| 504 |
Gateway Timeout |
Upstream service timeout |
