Add Anthropic built-in WebFetchTool support

docs/builtin-tools.md

@@ -315,9 +315,9 @@ allowing it to pull up-to-date information from the web.
 
 | 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. |
 | OpenAI | ❌ | |
-| Anthropic | ❌ | |
 | Groq | ❌ | |
 | Bedrock | ❌ | |
 | Mistral | ❌ | |
@@ -327,7 +327,23 @@ allowing it to pull up-to-date information from the web.
 
 ### Usage
 
-```py {title="url_context_basic.py"}
+```py {title="url_context_anthropic.py"}
+from pydantic_ai import Agent, UrlContextTool
+
+agent = Agent('anthropic:claude-sonnet-4-0', builtin_tools=[UrlContextTool()])
+
+result = agent.run_sync('What is the first sentence on https://ai.pydantic.dev?')
+print(result.output)
+"""
+Pydantic AI is a Python agent framework designed to make it less painful to build production grade applications with Generative AI.
+"""
+```
+
+_(This example is complete, it can be run "as is")_
+
+With Google, you can also use `UrlContextTool`:
+
+```py {title="url_context_google.py"}
 from pydantic_ai import Agent, UrlContextTool
 
 agent = Agent('google-gla:gemini-2.5-flash', builtin_tools=[UrlContextTool()])

pydantic_ai_slim/pydantic_ai/builtin_tools.py

@@ -171,6 +171,7 @@ class UrlContextTool(AbstractBuiltinTool):
 
     Supported by:
 
+    * Anthropic
     * Google
     """
 

pydantic_ai_slim/pydantic_ai/models/anthropic.py

@@ -13,7 +13,7 @@
 from .. import ModelHTTPError, UnexpectedModelBehavior, _utils, usage
 from .._run_context import RunContext
 from .._utils import guard_tool_call_id as _guard_tool_call_id
-from ..builtin_tools import CodeExecutionTool, MCPServerTool, MemoryTool, WebSearchTool
+from ..builtin_tools import CodeExecutionTool, MCPServerTool, MemoryTool, UrlContextTool, WebSearchTool
 from ..exceptions import UserError
 from ..messages import (
     BinaryContent,
@@ -106,12 +106,18 @@
         BetaToolUnionParam,
         BetaToolUseBlock,
         BetaToolUseBlockParam,
+        BetaWebFetchTool20250910Param,
+        BetaWebFetchToolResultBlock,
+        BetaWebFetchToolResultBlockParam,
         BetaWebSearchTool20250305Param,
         BetaWebSearchToolResultBlock,
         BetaWebSearchToolResultBlockContent,
         BetaWebSearchToolResultBlockParam,
         BetaWebSearchToolResultBlockParamContentParam,
     )
+    from anthropic.types.beta.beta_web_fetch_tool_result_block_param import (
+        Content as WebFetchToolResultBlockParamContent,
+    )
     from anthropic.types.beta.beta_web_search_tool_20250305_param import UserLocation
     from anthropic.types.model_param import ModelParam
 
@@ -371,6 +377,8 @@ def _process_response(self, response: BetaMessage) -> ModelResponse:
                 items.append(_map_web_search_tool_result_block(item, self.system))
             elif isinstance(item, BetaCodeExecutionToolResultBlock):
                 items.append(_map_code_execution_tool_result_block(item, self.system))
+            elif isinstance(item, BetaWebFetchToolResultBlock):
+                items.append(_map_web_fetch_tool_result_block(item, self.system))
             elif isinstance(item, BetaRedactedThinkingBlock):
                 items.append(
                     ThinkingPart(id='redacted_thinking', content='', signature=item.data, provider_name=self.system)
@@ -464,6 +472,9 @@ def _add_builtin_tools(
             elif isinstance(tool, CodeExecutionTool):  # pragma: no branch
                 tools.append(BetaCodeExecutionTool20250522Param(name='code_execution', type='code_execution_20250522'))
                 beta_features.append('code-execution-2025-05-22')
+            elif isinstance(tool, UrlContextTool):  # pragma: no branch
+                tools.append(BetaWebFetchTool20250910Param(name='web_fetch', type='web_fetch_20250910'))
+                beta_features.append('web-fetch-2025-09-10')
             elif isinstance(tool, MemoryTool):  # pragma: no branch
                 if 'memory' not in model_request_parameters.tool_defs:
                     raise UserError("Built-in `MemoryTool` requires a 'memory' tool to be defined.")
@@ -542,6 +553,7 @@ async def _map_message(  # noqa: C901
                     | BetaServerToolUseBlockParam
                     | BetaWebSearchToolResultBlockParam
                     | BetaCodeExecutionToolResultBlockParam
+                    | BetaWebFetchToolResultBlockParam
                     | BetaThinkingBlockParam
                     | BetaRedactedThinkingBlockParam
                     | BetaMCPToolUseBlockParam
@@ -604,6 +616,14 @@ async def _map_message(  # noqa: C901
                                     input=response_part.args_as_dict(),
                                 )
                                 assistant_content_params.append(server_tool_use_block_param)
+                            elif response_part.tool_name == UrlContextTool.kind:
+                                server_tool_use_block_param = BetaServerToolUseBlockParam(
+                                    id=tool_use_id,
+                                    type='server_tool_use',
+                                    name='web_fetch',
+                                    input=response_part.args_as_dict(),
+                                )
+                                assistant_content_params.append(server_tool_use_block_param)
                             elif (
                                 response_part.tool_name.startswith(MCPServerTool.kind)
                                 and (server_id := response_part.tool_name.split(':', 1)[1])
@@ -650,6 +670,19 @@ async def _map_message(  # noqa: C901
                                         ),
                                     )
                                 )
+                            elif response_part.tool_name == UrlContextTool.kind and isinstance(
+                                response_part.content, dict
+                            ):
+                                assistant_content_params.append(
+                                    BetaWebFetchToolResultBlockParam(
+                                        tool_use_id=tool_use_id,
+                                        type='web_fetch_tool_result',
+                                        content=cast(
+                                            WebFetchToolResultBlockParamContent,
+                                            response_part.content,  # pyright: ignore[reportUnknownMemberType]
+                                        ),
+                                    )
+                                )
                             elif response_part.tool_name.startswith(MCPServerTool.kind) and isinstance(
                                 response_part.content, dict
                             ):  # pragma: no branch
@@ -866,6 +899,11 @@ async def _get_event_iterator(self) -> AsyncIterator[ModelResponseStreamEvent]:
                         vendor_part_id=event.index,
                         part=_map_code_execution_tool_result_block(current_block, self.provider_name),
                     )
+                elif isinstance(current_block, BetaWebFetchToolResultBlock):  # pragma: lax no cover
+                    yield self._parts_manager.handle_part(
+                        vendor_part_id=event.index,
+                        part=_map_web_fetch_tool_result_block(current_block, self.provider_name),
+                    )
                 elif isinstance(current_block, BetaMCPToolUseBlock):
                     call_part = _map_mcp_server_use_block(current_block, self.provider_name)
                     builtin_tool_calls[call_part.tool_call_id] = call_part
@@ -972,7 +1010,14 @@ def _map_server_tool_use_block(item: BetaServerToolUseBlock, provider_name: str)
             args=cast(dict[str, Any], item.input) or None,
             tool_call_id=item.id,
         )
-    elif item.name in ('web_fetch', 'bash_code_execution', 'text_editor_code_execution'):  # pragma: no cover
+    elif item.name == 'web_fetch':
+        return BuiltinToolCallPart(
+            provider_name=provider_name,
+            tool_name=UrlContextTool.kind,
+            args=cast(dict[str, Any], item.input) or None,
+            tool_call_id=item.id,
+        )
+    elif item.name in ('bash_code_execution', 'text_editor_code_execution'):  # pragma: no cover
         raise NotImplementedError(f'Anthropic built-in tool {item.name!r} is not currently supported.')
     else:
         assert_never(item.name)
@@ -1008,6 +1053,16 @@ def _map_code_execution_tool_result_block(
     )
 
 
+def _map_web_fetch_tool_result_block(item: BetaWebFetchToolResultBlock, provider_name: str) -> BuiltinToolReturnPart:
+    return BuiltinToolReturnPart(
+        provider_name=provider_name,
+        tool_name=UrlContextTool.kind,
+        # Store just the content field (BetaWebFetchBlock) which has {content, type, url, retrieved_at}
+        content=item.content.model_dump(mode='json'),
+        tool_call_id=item.tool_use_id,
+    )
+
+
 def _map_mcp_server_use_block(item: BetaMCPToolUseBlock, provider_name: str) -> BuiltinToolCallPart:
     return BuiltinToolCallPart(
         provider_name=provider_name,