Agent Design Patterns

import anthropic

client = anthropic.Anthropic()

# --- Tool definition (what the model is allowed to call) ---
tools = [{
    "name": "search_docs",
    "description": "Search internal documentation for a query.",
    "input_schema": {
        "type": "object",
        "properties": {"query": {"type": "string"}},
        "required": ["query"],
    },
}]

def search_docs(query: str) -> str:
    # Real implementation would hit a vector store or search API
    return f"[results for '{query}': the deploy step runs 'make release']"

# --- The ReAct loop: reason -> act -> observe -> repeat ---
messages = [{"role": "user", "content": "How do I cut a release?"}]

while True:
    response = client.messages.create(
        model="claude-sonnet-5",
        max_tokens=1024,
        tools=tools,
        messages=messages,
    )
    messages.append({"role": "assistant", "content": response.content})

    # No tool requested -> the model has its final answer
    if response.stop_reason != "tool_use":
        answer = "".join(b.text for b in response.content if b.type == "text")
        print(answer)
        break

    # Execute every tool call the model asked for, feed results back
    tool_results = []
    for block in response.content:
        if block.type == "tool_use":
            result = search_docs(**block.input)
            tool_results.append({
                "type": "tool_result",
                "tool_use_id": block.id,
                "content": result,
            })
    messages.append({"role": "user", "content": tool_results})

def reflect_and_improve(client, task: str, max_rounds: int = 2) -> str:
    """Generate a draft, then critique and revise it until approved."""

    draft = client.messages.create(
        model="claude-sonnet-5", max_tokens=1024,
        messages=[{"role": "user", "content": task}],
    ).content[0].text

    for _ in range(max_rounds):
        critique = client.messages.create(
            model="claude-sonnet-5", max_tokens=512,
            messages=[{"role": "user", "content": (
                "Critique the draft against the task. List concrete, "
                "actionable flaws only. If it is genuinely good, reply "
                f"exactly 'APPROVED'.\n\nTask: {task}\n\nDraft:\n{draft}"
            )}],
        ).content[0].text

        if "APPROVED" in critique:
            break

        draft = client.messages.create(
            model="claude-sonnet-5", max_tokens=1024,
            messages=[{"role": "user", "content": (
                "Revise the draft to fix every point in the critique. "
                f"Return only the improved draft.\n\nCritique:\n{critique}"
                f"\n\nDraft:\n{draft}"
            )}],
        ).content[0].text

    return draft

def route(client, query: str) -> str:
    """Classify the query once with a cheap model, then dispatch."""

    label = client.messages.create(
        model="claude-haiku-4-5-20251001",  # fast + cheap for classification
        max_tokens=10,
        system=(
            "Classify the user query into exactly one label: "
            "BILLING, TECHNICAL, or SALES. Reply with only the label."
        ),
        messages=[{"role": "user", "content": query}],
    ).content[0].text.strip().upper()

    handlers = {
        "BILLING": handle_billing,      # each handler can use a
        "TECHNICAL": handle_technical,  # different model, prompt,
        "SALES": handle_sales,          # and tool set
    }
    handler = handlers.get(label, handle_general)
    return handler(query)