Claude API Cheatsheet | Spider On The Web

⚡ Quick Start

import anthropic

client = anthropic.Anthropic(
    api_key="your-api-key"
)

message = client.messages.create(
    model="claude-sonnet-4-20250514",
    max_tokens=1024,
    messages=[
        {"role": "user", "content": "Hello, Claude!"}
    ]
)

print(message.content[0].text)

import Anthropic from '@anthropic-ai/sdk';

const client = new Anthropic({
    apiKey: 'your-api-key'
});

const message = await client.messages.create({
    model: 'claude-sonnet-4-20250514',
    max_tokens: 1024,
    messages: [
        { role: 'user', content: 'Hello, Claude!' }
    ]
});

console.log(message.content[0].text);

curl https://api.anthropic.com/v1/messages \
  -H "x-api-key: your-api-key" \
  -H "anthropic-version: 2023-06-01" \
  -H "content-type: application/json" \
  -d '{
    "model": "claude-sonnet-4-20250514",
    "max_tokens": 1024,
    "messages": [
      {"role": "user", "content": "Hello, Claude!"}
    ]
  }'

🤖 Available Models

Model	ID	Context	Best For
Claude Opus 4	`claude-opus-4-20250514`	200K	Complex reasoning, coding
Claude Sonnet 4	`claude-sonnet-4-20250514`	200K	Balanced performance
Claude Haiku 3.5	`claude-3-5-haiku-20241022`	200K	Speed, simple tasks

Tip: Use claude-sonnet-4-20250514 as your default. It balances quality and cost well for most use cases.

⚙️ Key Parameters

Parameter	Type	Required	Description
`model`	string	Yes	Model ID to use
`max_tokens`	integer	Yes	Maximum tokens in response
`messages`	array	Yes	Conversation messages
`system`	string	No	System prompt
`temperature`	float	No	0-1, randomness (default: 1)
`top_p`	float	No	0-1, nucleus sampling
`stream`	boolean	No	Enable streaming response

📝 System Prompts

Set Claude's behavior and context at the start of the conversation.

message = client.messages.create(
    model="claude-sonnet-4-20250514",
    max_tokens=1024,
    system="You are a senior Python developer. Write clean, 
well-documented code with type hints. Always explain 
your reasoning before showing code.",
    messages=[
        {"role": "user", "content": "Write a function to validate emails"}
    ]
)

💬 Multi-turn Conversations

messages = [
    {"role": "user", "content": "What is Python?"},
    {"role": "assistant", "content": "Python is a high-level programming language..."},
    {"role": "user", "content": "Show me a simple example"}
]

response = client.messages.create(
    model="claude-sonnet-4-20250514",
    max_tokens=1024,
    messages=messages
)

Note: Messages must alternate between user and assistant roles. Always start with a user message.

🌊 Streaming Responses

with client.messages.stream(
    model="claude-sonnet-4-20250514",
    max_tokens=1024,
    messages=[{"role": "user", "content": "Write a haiku"}]
) as stream:
    for text in stream.text_stream:
        print(text, end="", flush=True)

👁️ Vision (Image Input)

import base64

# Read and encode image
with open("image.png", "rb") as f:
    image_data = base64.standard_b64encode(f.read()).decode("utf-8")

message = client.messages.create(
    model="claude-sonnet-4-20250514",
    max_tokens=1024,
    messages=[{
        "role": "user",
        "content": [
            {
                "type": "image",
                "source": {
                    "type": "base64",
                    "media_type": "image/png",
                    "data": image_data
                }
            },
            {
                "type": "text",
                "text": "What's in this image?"
            }
        ]
    }]
)

⚠️ Error Handling

import anthropic

try:
    message = client.messages.create(...)
except anthropic.APIConnectionError:
    print("Failed to connect to API")
except anthropic.RateLimitError:
    print("Rate limited - wait and retry")
except anthropic.APIStatusError as e:
    print(f"API error: {e.status_code}")

Error	Code	Cause
Rate Limit	`429`	Too many requests
Invalid Request	`400`	Bad parameters
Authentication	`401`	Invalid API key
Overloaded	`529`	API temporarily overloaded

✅ Best Practices

Set max_tokens appropriately - don't default to maximum
Use system prompts to define behavior and constraints
Implement exponential backoff for rate limits
Use streaming for long responses to improve UX
Store API keys in environment variables, never in code
Lower temperature (0.0-0.3) for factual/coding tasks