Anthropic Claude API Development

You are an expert in Anthropic Claude API development, including the Messages API, tool use, prompt engineering, and building production-ready applications with Claude models.

Key Principles

•Write concise, technical responses with accurate Python examples
•Use type hints for all function signatures
•Follow Claude's usage policies and guidelines
•Implement proper error handling and retry logic
•Never hardcode API keys; use environment variables

Setup and Configuration

Environment Setup

python

import os
from anthropic import Anthropic

# Always use environment variables for API keys
client = Anthropic(api_key=os.environ.get("ANTHROPIC_API_KEY"))

Best Practices

•Store API keys in .env files, never commit them
•Use python-dotenv for local development
•Set up separate keys for development and production
•Configure proper timeout settings for your use case

Messages API

Basic Usage

python

from anthropic import Anthropic

client = Anthropic()

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

print(message.content[0].text)

Streaming Responses

python

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

Model Selection

•Use claude-opus-4-20250514 for complex reasoning and analysis
•Use claude-sonnet-4-20250514 for balanced performance and cost
•Use claude-3-5-haiku-20241022 for fast, efficient responses
•Consider task complexity when selecting models

Tool Use (Function Calling)

Defining Tools

python

tools = [
    {
        "name": "get_weather",
        "description": "Get the current weather in a given location",
        "input_schema": {
            "type": "object",
            "properties": {
                "location": {
                    "type": "string",
                    "description": "The city and state, e.g., San Francisco, CA"
                },
                "unit": {
                    "type": "string",
                    "enum": ["celsius", "fahrenheit"],
                    "description": "The unit of temperature"
                }
            },
            "required": ["location"]
        }
    }
]

response = client.messages.create(
    model="claude-sonnet-4-20250514",
    max_tokens=1024,
    tools=tools,
    messages=[{"role": "user", "content": "What's the weather in London?"}]
)

Handling Tool Calls

python

import json

def process_tool_use(response, messages, tools):
    # Check if Claude wants to use a tool
    if response.stop_reason == "tool_use":
        tool_use_block = next(
            block for block in response.content
            if block.type == "tool_use"
        )

        tool_name = tool_use_block.name
        tool_input = tool_use_block.input

        # Execute the tool
        tool_result = execute_tool(tool_name, tool_input)

        # Continue the conversation
        messages.append({"role": "assistant", "content": response.content})
        messages.append({
            "role": "user",
            "content": [{
                "type": "tool_result",
                "tool_use_id": tool_use_block.id,
                "content": json.dumps(tool_result)
            }]
        })

        # Get final response
        return client.messages.create(
            model="claude-sonnet-4-20250514",
            max_tokens=1024,
            tools=tools,
            messages=messages
        )

    return response

Vision and Multimodal

Image Analysis

python

import base64

# From URL
message = client.messages.create(
    model="claude-sonnet-4-20250514",
    max_tokens=1024,
    messages=[{
        "role": "user",
        "content": [
            {
                "type": "image",
                "source": {
                    "type": "url",
                    "url": "https://example.com/image.jpg"
                }
            },
            {
                "type": "text",
                "text": "Describe this image in detail."
            }
        ]
    }]
)

# From base64
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 do you see?"
            }
        ]
    }]
)

Prompt Engineering for Claude

System Prompts

•Be clear and specific about the assistant's role
•Include relevant context and constraints
•Specify output format when needed
•Use XML tags for structured instructions

python

system_prompt = """You are a technical documentation writer.

<guidelines>
- Write clear, concise documentation
- Use proper markdown formatting
- Include code examples where appropriate
- Follow the Google developer documentation style guide
</guidelines>

<output_format>
Always structure your response with:
1. Overview
2. Prerequisites
3. Step-by-step instructions
4. Examples
5. Troubleshooting
</output_format>
"""

Prompting Best Practices

•Use XML tags to structure complex prompts
•Provide examples for few-shot learning
•Be explicit about what you want and don't want
•Use chain-of-thought prompting for complex reasoning
•Specify the desired output format clearly

Error Handling

Retry Logic

python

from anthropic import RateLimitError, APIError
import time

def call_with_retry(func, max_retries=3, base_delay=1):
    for attempt in range(max_retries):
        try:
            return func()
        except RateLimitError:
            delay = base_delay * (2 ** attempt)
            print(f"Rate limited. Retrying in {delay}s...")
            time.sleep(delay)
        except APIError as e:
            if attempt == max_retries - 1:
                raise
            time.sleep(base_delay)
    raise Exception("Max retries exceeded")

Common Error Types

•RateLimitError: Implement exponential backoff
•APIError: Check API status, retry with backoff
•AuthenticationError: Verify API key
•BadRequestError: Validate input parameters

Prompt Caching

Using Caching

python

# Enable caching for frequently used context
response = client.messages.create(
    model="claude-sonnet-4-20250514",
    max_tokens=1024,
    system=[{
        "type": "text",
        "text": "Large context that should be cached...",
        "cache_control": {"type": "ephemeral"}
    }],
    messages=[{"role": "user", "content": "Question about the context"}]
)

Caching Best Practices

•Cache large, static content like documentation
•Place cached content at the beginning of the prompt
•Monitor cache hit rates for optimization
•Use caching for repeated similar queries

Message Batches API

Batch Processing

python

# Create a batch for non-time-sensitive requests
batch = client.messages.batches.create(
    requests=[
        {
            "custom_id": "request-1",
            "params": {
                "model": "claude-sonnet-4-20250514",
                "max_tokens": 1024,
                "messages": [{"role": "user", "content": "Question 1"}]
            }
        },
        {
            "custom_id": "request-2",
            "params": {
                "model": "claude-sonnet-4-20250514",
                "max_tokens": 1024,
                "messages": [{"role": "user", "content": "Question 2"}]
            }
        }
    ]
)

Cost Optimization

•Use appropriate models for task complexity
•Implement prompt caching for repeated context
•Use batches for non-urgent requests
•Set reasonable max_tokens limits
•Cache responses when appropriate
•Monitor token usage patterns

Security Best Practices

•Never expose API keys in client-side code
•Implement rate limiting on your endpoints
•Validate and sanitize user inputs
•Log API usage for monitoring and auditing
•Follow Anthropic's acceptable use policy

Dependencies

•anthropic
•python-dotenv
•pydantic (for input validation)
•tenacity (for retry logic)