WebSearchTool max_uses parameter ignored in Anthropic model integration

[eballesteros]

Initial Checks

• I confirm that I'm using the latest version of Pydantic AI
• I confirm that I searched for my issue in https://github.com/pydantic/pydantic-ai/issues before opening this issue

Description

max_uses appears both as a parameter in WebSearchTool and in the anthropic docs as a mechanism to limits the number of searches performed, but at the moment has no effect.

When a WebSearchTool with max_uses specified is passed to an Anthropic model, the parameter is not forwarded to the underlying BetaWebSearchTool20250305Param, causing the limitation to have no effect.

In .../models/anthropic.py at lines 355-375, the _get_builtin_tools method processes WebSearchTool instances but only forwards allowed_domains, blocked_domains, and user_location to the Anthropic API parameter object. The max_uses field is omitted.

If I'm not mistaken, it should be a 1 line change. I'd be happy to open a PR.

Example Code

import asyncio

from pydantic_ai import Agent
from pydantic_ai.models.anthropic import AnthropicModel
from pydantic_ai.builtin_tools import WebSearchTool


async def main():
    agent = Agent(
        model=AnthropicModel('claude-sonnet-4-20250514'),
        builtin_tools=[WebSearchTool(max_uses=1)],
        instructions="You are a helpful assistant. Use web search to answer questions."
    )

    result = await agent.run("What is the birthdate of the CEO of the most valuable company in the S&P 500 as of July 2025?")

    print(result.output)

asyncio.run(main())

Python, Pydantic AI & LLM client version

Python 3.12.8
pydantic-ai-slim 0.7.1
anthropic 0.64.0

[DouweM]

@eballesteros Good catch, and I agree it looks like a oneliner, PR would be much appreciated!