> ## Documentation Index
> Fetch the complete documentation index at: https://docs.cycls.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Anthropic Claude

> Build an AI agent using Claude and the Claude Agent SDK.

This guide shows you how to build an agent using Anthropic's Claude models with the Claude Agent SDK, which provides tool use capabilities out of the box.

## Prerequisites

* Python 3.9+
* `cycls` package installed
* Anthropic API key
* Docker installed (for local testing)

```bash theme={null}
pip install cycls
```

## Basic Claude Agent

Create a file called `app.py`:

```python theme={null}
import cycls

@cycls.app(pip=["anthropic"], copy=[".env"])
async def app(context):
    from anthropic import AsyncAnthropic

    client = AsyncAnthropic()

    async with client.messages.stream(
        model="claude-sonnet-4-20250514",
        max_tokens=1024,
        messages=context.messages
    ) as stream:
        async for text in stream.text_stream:
            yield text

app.local()
```

Create a `.env` file:

```env theme={null}
ANTHROPIC_API_KEY=sk-ant-...
```

Run the agent:

```bash theme={null}
python app.py
```

## Claude Agent SDK with Tools

For more advanced use cases, you can use the Claude Agent SDK which provides built-in tool support:

```python theme={null}
import cycls

@cycls.app(pip=["claude-agent-sdk"], copy=[".env"])
async def app(context):
    from claude_agent_sdk import (
        ClaudeSDKClient,
        ClaudeAgentOptions,
        AssistantMessage,
        TextBlock,
        ToolUseBlock,
        ThinkingBlock,
        ResultMessage,
    )

    async with ClaudeSDKClient(
        options=ClaudeAgentOptions(
            allowed_tools=["Read", "Edit", "Glob", "Grep", "Bash", "WebSearch"],
            permission_mode="acceptEdits",
        )
    ) as client:
        await client.query(context.last_message)

        async for message in client.receive_response():
            if isinstance(message, AssistantMessage):
                for block in message.content:
                    if isinstance(block, TextBlock):
                        yield block.text
                    elif isinstance(block, ThinkingBlock):
                        yield {"type": "thinking", "thinking": block.thinking}
                    elif isinstance(block, ToolUseBlock):
                        yield {"type": "thinking", "thinking": f"Using tool: {block.name}"}

            elif isinstance(message, ResultMessage):
                yield {"type": "thinking", "thinking": "Tool completed"}

app.local()
```

This example:

* Uses the Claude Agent SDK for tool-based interactions
* Streams text responses directly to the user
* Shows thinking blocks for reasoning visibility
* Displays tool usage as thinking bubbles

## Configuration

Create a `.env` file with your API key:

```env theme={null}
ANTHROPIC_API_KEY=sk-ant-...
```

## Deploy to Cloud

```python theme={null}
import cycls
import os

cycls.api_key = os.getenv("CYCLS_API_KEY")

@cycls.app(pip=["anthropic"], copy=[".env"])
async def app(context):
    from anthropic import AsyncAnthropic

    client = AsyncAnthropic()

    async with client.messages.stream(
        model="claude-sonnet-4-20250514",
        max_tokens=1024,
        messages=context.messages
    ) as stream:
        async for text in stream.text_stream:
            yield text

app.deploy()
```