A Raw HTTP Call: What the SDK Does for You

It is just HTTP and JSON

Any language that can send HTTPS and parse JSON can call these APIs. Doing it once by hand removes the mystery: build the JSON body, add the headers (an API key header, a content type, and for Anthropic an anthropic-version header), send a POST, check the status code and parse the JSON. SDKs add real value on top: typed request and response objects, automatic retries with backoff, timeouts, streaming helpers, error classes and pagination. Use the SDK in applications; use raw HTTP for debugging, unusual languages or when you need exact control.

A raw call with urllib, run

I ran this in a Python virtual environment with the anthropic 1.11.0 and openai 3.22.1 SDKs against a small local stand-in server (shown in the testing topic, saved as mock.py). The server returns canned replies, so no key, network or real model is involved: it proves how the SDK builds requests and handles replies, not what a real model would say. The code sends a Messages-style request with urllib only, to the local stand-in server. It prints the status, the text, the usage and what the server actually received: the key header and the three required body fields.

import json, urllib.request, mock
srv = mock.start(); base = f"http://127.0.0.1:{srv.server_address[1]}"

req = urllib.request.Request(base + "/v1/messages", method="POST",
    data=json.dumps({"model": "demo-model", "max_tokens": 100,
                     "messages": [{"role": "user", "content": "Capital of France?"}]}).encode(),
    headers={"x-api-key": "sk-test-123", "anthropic-version": "2023-06-01", "content-type": "application/json"})
with urllib.request.urlopen(req) as r:
    reply = json.load(r)
print("status OK, stop_reason:", reply["stop_reason"])
print("text:", reply["content"][0]["text"])
print("usage:", reply["usage"])
seen = mock.STATE["log"][-1]
print("server saw header x-api-key:", seen["headers"]["x-api-key"])
print("server saw body keys:", sorted(seen["body"]))

Output:

status OK, stop_reason: end_turn
text: Paris is the capital of France.
usage: {'input_tokens': 14, 'output_tokens': 8}
server saw header x-api-key: sk-test-123
server saw body keys: ['max_tokens', 'messages', 'model']

Quick check: What do SDKs add on top of raw HTTP?

• No need for a key
• A different model
• Free tokens
• Typed objects, retries, timeouts and streaming helpers