Quick Reference: API Commands

Updated: 2026-05-26

Base URL and Headers

Item	Value
Base URL	https://api.anthropic.com/v1
API Key Header	x-api-key: $ANTHROPIC_API_KEY
Version Header	anthropic-version: 2023-06-01
Content Type	application/json

Core Endpoints

Endpoint	Method	Purpose
/messages	POST	Send a message to Claude
/messages/count_tokens	POST	Count tokens for a message
/models	GET	List available models
/beta/skills	POST	Create a skill
/beta/skills/versions	POST	Create a skill version
/beta/files	GET	List files
/beta/files	POST	Upload a file

Key Parameters

Parameter	Type	Required	Default	Description
model	string	Yes	-	Model ID (e.g., claude-sonnet-4-6)
max_tokens	integer	Yes	-	Maximum tokens in response
messages	array	Yes	-	Conversation messages
system	string	No	-	System prompt
temperature	float	No	1.0	Sampling temperature (0-1)
top_p	float	No	-	Nucleus sampling threshold
stream	boolean	No	false	Enable streaming
tools	array	No	-	Tool definitions
tool_choice	object	No	auto	How to select tools
stop_sequences	array	No	-	Custom stop sequences
metadata	object	No	-	Request metadata

cURL Template

curl https://api.anthropic.com/v1/messages \
  -H "x-api-key: $ANTHROPIC_API_KEY" \
  -H "anthropic-version: 2023-06-01" \
  -H "content-type: application/json" \
  -d '{
    "model": "claude-sonnet-4-6",
    "max_tokens": 1024,
    "messages": [{"role": "user", "content": "..."}]
  }'

Python SDK Template

from anthropic import Anthropic

client = Anthropic(api_key="sk-ant-...")

response = client.messages.create(
    model="claude-sonnet-4-6",
    max_tokens=1024,
    messages=[{"role": "user", "content": "..."}]
)

print(response.content[0].text)

Gotchas

Issue	Fix
401 Unauthorized	Check API key format: must start with sk-ant-
max_tokens missing	Required parameter, not optional
Tool schema invalid	Must be valid JSON Schema with type: "object"
Stream parsing	Parse data: prefix from SSE lines
Image format	Use base64 with media_type (image/jpeg, image/png, etc.)
System prompt placement	system is a top-level field, not in messages