HTTP Methods and Their Guarantees

Safe and idempotent

Safe methods do not change server state (GET, HEAD, OPTIONS), so clients, caches and crawlers may call them freely. Idempotent methods give the same end state when repeated (GET, PUT, DELETE, and by design HEAD/OPTIONS), which makes retries safe after a timeout. POST is neither: repeating it may create a second resource. PUT replaces a whole resource at a known URL; PATCH applies a partial change; DELETE removes a resource (deleting something already gone should still be fine). Never use GET for state changes, since links, prefetchers and caches will trigger them.

Method guarantees at a glance

Use this table when deciding which method fits an operation.

Method   Safe  Idempotent  Typical use
GET      yes   yes         read a resource or a collection
HEAD     yes   yes         headers only (check existence, size, ETag)
PUT      no    yes         replace a resource at a known URL
PATCH    no    no*         partial update (*can be made idempotent)
DELETE   no    yes         remove a resource
POST     no    no          create, or run an action

JSON Merge Patch for PATCH, run

I ran this plain-Python example. JSON Merge Patch (RFC 7396) is a simple partial-update format: keys in the patch replace or are added, nested objects merge, and a null value deletes the key. Arrays are replaced whole. Here pin is removed, state added and tags replaced.

import hmac, hashlib, json, time, bisect

def merge_patch(target, patch):
    if not isinstance(patch, dict): return patch
    result = dict(target) if isinstance(target, dict) else {}
    for k, v in patch.items():
        if v is None: result.pop(k, None)
        else: result[k] = merge_patch(result.get(k), v)
    return result
doc = {"name": "Asha", "address": {"city": "Pune", "pin": "411001"}, "tags": ["a"]}
print(merge_patch(doc, {"address": {"pin": None, "state": "MH"}, "tags": ["x", "y"], "name": "Asha R"}))

Output:

{'name': 'Asha R', 'address': {'city': 'Pune', 'state': 'MH'}, 'tags': ['x', 'y']}

Quick check: Which method is idempotent and replaces a whole resource?

• OPTIONS
• POST
• GET
• PUT