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@sarth6 sarth6 commented Nov 14, 2025

Closes #2971

  • Allows users to use the WebFetchTool builtin tool for Anthropic/Google models, which uses the (Claude WebFetch tool / Google URL Context tool) under-the-hood
  • Deprecates Pydantic AI UrlContextTool (which was Google-only) as users should now use WebFetchTool instead
  • Includes the Anthropic BetaWebFetchToolResultBlockParam Content (web fetch url / retrieved_at / source data / etc) in the Pydantic AI BuiltinToolReturnPart that arrives in the agent message history, so that Pydantic AI users have access to the full web fetch tool return object
  • Allows users to supply various tool config params to the Pydantic AI WebFetchTool that get passed to the Claude WebFetch tool under-the-hood; these params are not supported by Google's UrlContextToolDict unfortunately

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sarth6 commented Nov 14, 2025

@DouweM would you prefer if we renamed UrlContextTool to WebFetchTool and left UrlContextTool in a google-only deprecated state?

@sarth6 sarth6 marked this pull request as ready for review November 18, 2025 05:37

_(This example is complete, it can be run "as is")_

With Google, you can also use `UrlContextTool`:
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We just need one example as the only difference is the model name.

Per the above, let's not mention UrlContextTool anymore.

Should we support any of the options on https://docs.claude.com/en/docs/agents-and-tools/tool-use/web-fetch-tool#tool-definition? If so, that'd warrant a new section and Anthropic-specific example. But ideally Google would also support at least some of those.

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Good idea! I'll look into adding those options

assert len(tool_calls) >= 1
assert len(tool_returns) >= 1
assert any(tc.tool_name == 'url_context' for tc in tool_calls)
assert any(tr.tool_name == 'url_context' for tr in tool_returns)
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Please use full snapshots like in the other builtin tool tests

'Pydantic AI is a Python agent framework designed to help you quickly, confidently, and painlessly build production grade applications and workflows with Generative AI.'
)

messages = agent_run.result.all_messages()
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Same as above; full snapshots of messages and events please



@pytest.mark.vcr()
async def test_anthropic_url_context_tool_multi_turn(allow_model_requests: None, anthropic_api_key: str):
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See tests for other builtin tools: we typically check this by having 2 agent.runs in the same non-streaming test, where the second takes the history of the first to ensure that the API accepts it.

assert len(anthropic_messages) == 0 # No messages should be added


@pytest.mark.vcr()
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Why were these changes necessary?

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Unecessary, my bad - removed 👍

)

result = await agent.run('How much is 3 * 12390?')
result = await agent.run('How much is 3 * 12390?') # pragma: lax no cover
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Please remove all the new # pragma: lax no covers, I don't think they should be needed

@sarth6 sarth6 changed the title Add UrlContextTool support for Anthropic models Add WebFetchTool builtin tool support Nov 18, 2025
@sarth6 sarth6 requested a review from DouweM November 19, 2025 00:39
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sarth6 commented Nov 19, 2025

@DouweM I ended up adding the Anthropic WebFetch params to our new builtin tool, but looks like Google's URL Context Tool doesn't support any of them as far as I could see from their docs, as the UrlContextToolDict schema is empty

https://ai.google.dev/gemini-api/docs/url-context#contextual-response

| Provider | Supported | Notes |
|----------|-----------|-------|
| Anthropic || Full feature support. Uses Anthropic's [Web Fetch Tool](https://docs.claude.com/en/docs/agents-and-tools/tool-use/web-fetch-tool) internally to retrieve URL contents. |
| Google || No [`BuiltinToolCallPart`][pydantic_ai.messages.BuiltinToolCallPart] or [`BuiltinToolReturnPart`][pydantic_ai.messages.BuiltinToolReturnPart] is currently generated; please submit an issue if you need this. Using built-in tools and function tools (including [output tools](output.md#tool-output)) at the same time is not supported; to use structured output, use [`PromptedOutput`](output.md#prompted-output) instead. |
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While we're at it, would you be up for fixing "No [BuiltinToolCallPart][pydantic_ai.messages.BuiltinToolCallPart] or [BuiltinToolReturnPart][pydantic_ai.messages.BuiltinToolReturnPart] is currently generated"?

Per https://ai.google.dev/gemini-api/docs/url-context#contextual-response the data is available, and I see the same in the test_google_model_url_context_tool cassette, so you should be able to get it to transform into parts nicely without even needing to regenerate the cassette (although I suppose we'd ideally want a streaming test + cassette as well).

It may be better to do that in a future PR (not necessarily you), unless you feel like doing it now :)


_(This example is complete, it can be run "as is")_

### Parameters
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We call them Configuration Options in all the other examples; please make sure the wording is consistent, as well as the way the table is structured, the Provider Support subsection, etc.

With Anthropic, you can only use one of `blocked_domains` or `allowed_domains`, not both.

!!! note
Google's URL context tool does not support any configuration parameters. The limits are fixed at 20 URLs per request with a maximum of 34MB per URL.
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This should be in a Provider Support Notes column



# Remove UrlContextTool from _BUILTIN_TOOL_TYPES and restore WebFetchTool
# This ensures the discriminated union only includes WebFetchTool
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Would that cause issues with old payloads that are being deserialized now? Or old code that is now giving a deprecation warning but hasn't actually been updated yet? Would be worth testing in test_builtin_tools.

tools.append(BetaCodeExecutionTool20250522Param(name='code_execution', type='code_execution_20250522'))
beta_features.append('code-execution-2025-05-22')
elif isinstance(tool, WebFetchTool): # pragma: no branch
citations = BetaCitationsConfigParam(enabled=tool.citations_enabled) if tool.citations_enabled else None
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Let's name our field enable_citations,

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Support Anthropic Web Fetch built-in tool

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