Introduction

Building applications with the Claude API can be complex—especially when you're juggling multiple languages, streaming patterns, tool use, and batch processing. The Claude API Skill is an open-source Agent Skill designed to simplify this process. It equips Claude with detailed, up-to-date reference material for two primary Anthropic surfaces: the Messages API and Claude Managed Agents (beta).

This guide will walk you through what the skill provides, how it activates, and how you can use it to build smarter, more efficient Claude-powered applications.

What Is the Claude API Skill?

The Claude API Skill is a specialized knowledge module that Claude can load when you're working with Anthropic's APIs. It's bundled with Claude Code and also available in the open-source Anthropic skills repository. Once installed, it gives Claude:

• Language-specific SDK documentation for Python, TypeScript, Java, Go, Ruby, C#, PHP, and cURL (Messages API) and 7 languages for Managed Agents (C# not supported).
• Tool use guidance with language-specific examples and conceptual foundations.
• Streaming patterns for building chat UIs and handling incremental display.
• Batch processing details for offline processing at 50% cost.
• Prompt caching best practices, including breakpoint placement and silent-invalidator audit.
• Model migration steps for moving to newer Claude models (including breaking changes on Claude Opus 4.7).
• Current model information (IDs, context window sizes, pricing).
• Common pitfalls and how to avoid them.

For Managed Agents, the skill also includes an onboarding flow, client patterns (lossless stream reconnect, interrupt handling, file-mount gotchas), and deployment constraints.

How Progressive Disclosure Works

One of the skill's most powerful features is progressive disclosure. Instead of loading the entire documentation set at once (which would waste context), Claude loads only the documentation relevant to:

• Your project's programming language
• The surface you're using (Messages API or Managed Agents)
• The specific task (tool use, streaming, batch processing, etc.)

This keeps context efficient and responses fast.

When the Skill Activates

The skill activates automatically in these scenarios:

• Your code imports an Anthropic SDK (e.g., anthropic for Python, @anthropic-ai/sdk for TypeScript/JavaScript)
• You ask Claude to help build, debug, or optimize something with the Claude API, an Anthropic SDK, or Managed Agents
• You add, modify, or tune a Claude feature in a file (like prompt caching or tool definitions)

You can also trigger it manually by asking Claude to "use the Claude API skill" or by running the /claude-api command in supported environments.

Practical Examples

Example 1: Using the Messages API with Python

Once the skill is active, you can ask Claude to generate code for the Messages API. Here's a simple example:

import anthropic
client = anthropic.Anthropic()
message = client.messages.create(
    model="claude-sonnet-4-20250514",
    max_tokens=1024,
    messages=[
        {"role": "user", "content": "Explain quantum computing in simple terms."}
    ]
)
print(message.content[0].text)

The skill will provide the correct import, client initialization, and message structure based on the latest SDK version.

Example 2: Tool Use with TypeScript

import Anthropic from '@anthropic-ai/sdk';
const client = new Anthropic();
const response = await client.messages.create({
  model: 'claude-sonnet-4-20250514',
  max_tokens: 1024,
  tools: [{
    name: 'get_weather',
    description: 'Get the current weather for a location',
    input_schema: {
      type: 'object',
      properties: {
        location: { type: 'string' }
      },
      required: ['location']
    }
  }],
  messages: [{ role: 'user', content: 'What\'s the weather in Tokyo?' }]
});
// Handle tool use
if (response.stop_reason === 'tool_use') {
  console.log('Tool call:', response.content);
}

Example 3: Batch Processing (50% Cost Savings)

import anthropic
from anthropic import Anthropic
client = Anthropic()
Create a batch of messages
requests = [
    {
        "custom_id": "req-1",
        "params": {
            "model": "claude-sonnet-4-20250514",
            "max_tokens": 1024,
            "messages": [{"role": "user", "content": "What is the capital of France?"}]
        }
    },
    {
        "custom_id": "req-2",
        "params": {
            "model": "claude-sonnet-4-20250514",
            "max_tokens": 1024,
            "messages": [{"role": "user", "content": "What is the capital of Japan?"}]
        }
    }
]
batch = client.batches.create(requests=requests)
print(f"Batch created with ID: {batch.id}")

Example 4: Managed Agents Onboarding

The skill includes an interview-driven onboarding flow for Managed Agents. You can start it with:

/claude-api managed-agents-onboard

This will walk you through creating a persistent agent, setting up sessions, and handling tool confirmations.

Best Practices

• Let progressive disclosure work for you – Don't ask for all documentation at once. Focus on your specific task (e.g., "Show me streaming patterns for Python").
• Use the skill early – Activate it at the start of a new project to get the latest SDK patterns and avoid deprecated methods.
• Combine with other skills – The Claude API Skill works well alongside other Agent Skills like the Memory Skill or Web Fetch Skill.
• Check for updates – The skill is updated regularly. If you're using it via the open-source repository, pull the latest version periodically.
• Leverage model migration guidance – When upgrading to a new Claude model, use the skill to get step-by-step migration steps, including breaking changes.

Limitations to Keep in Mind

• Managed Agents are first-party only – They are not available on Amazon Bedrock, Google Vertex AI, or Microsoft Foundry. The skill will route third-party deployments to Messages API + tool use instead.
• C# support is limited – C# is supported for the Messages API but not for Managed Agents.
• Context window still matters – While progressive disclosure helps, very large projects may still require careful context management.

Conclusion

The Claude API Skill is an essential tool for any developer building with Anthropic's APIs. By providing up-to-date, language-specific, and task-relevant documentation, it reduces friction, speeds up development, and helps you avoid common mistakes. Whether you're using the Messages API for custom agent loops or exploring Managed Agents for stateful applications, this skill will make your workflow smoother and more productive.

Key Takeaways

• The Claude API Skill provides language-specific, up-to-date documentation for the Messages API and Managed Agents, using progressive disclosure to keep context efficient.
• It activates automatically when you import an Anthropic SDK or ask Claude to help with API-related tasks.
• You can use it for tool use, streaming, batch processing, prompt caching, model migration, and more.
• Managed Agents are first-party only; the skill routes third-party deployments to Messages API + tool use.
• For best results, let progressive disclosure guide your queries and combine the skill with other Agent Skills as needed.