fix(bedrock): explain why Anthropic's web_search server tool is rejected

Bedrock hosts none of Anthropic's web_search server tools, so forwarding
one earns an opaque "The provided request is not valid" from AWS that
names neither the tool nor a way forward. Every Claude model on Bedrock
fails the same way, which reads as a broken deployment rather than an
unsupported capability.

Reject it in the Bedrock Invoke messages transform with a message naming
the tool and the web-search interception settings that do serve it.
Interception rewrites the tool into LiteLLM's own search tool before this
point, so the guard only fires when it is not configured and the working
path is untouched.

Resolves LIT-5391

litellm/llms/bedrock/messages/invoke_transformations/anthropic_claude3_transformation.py

@@ -1,4 +1,4 @@
-from collections.abc import AsyncIterator
+from collections.abc import AsyncIterator, Mapping
 from typing import TYPE_CHECKING, Any, Final, cast
 
 import httpx
@@ -56,6 +56,9 @@ else:
     LiteLLMLoggingObj = Any
 
 
+UNSUPPORTED_BEDROCK_SERVER_TOOL_PREFIX: Final = "web_search_"
+
+
 class AmazonAnthropicClaudeMessagesConfig(
     AnthropicMessagesConfig,
     AmazonInvokeConfig,
@@ -605,6 +608,39 @@ class AmazonAnthropicClaudeMessagesConfig(
         normalize_bedrock_opus_output_config_effort(model=model, output_config=clamped)
         optional_params["reasoning_effort"] = clamped["effort"]
 
+    def _reject_unsupported_server_tools(self, anthropic_messages_request: Mapping[str, object], model: str) -> None:
+        """Bedrock hosts none of Anthropic's ``web_search_*`` server tools, so
+        forwarding one earns an opaque ``The provided request is not valid`` from
+        AWS that names neither the tool nor a way forward. Web-search
+        interception rewrites the tool before this point, so reaching here means
+        it is not configured for this request.
+        """
+        tools: Final = anthropic_messages_request.get("tools")
+        if not isinstance(tools, list):
+            return
+        entries: Final = cast(list[Mapping[str, object]], tools)  # cast-ok: request body is untyped upstream
+        unsupported: Final = sorted(
+            {
+                tool_type
+                for tool in entries
+                if isinstance(tool_type := tool.get("type"), str)
+                if tool_type.startswith(UNSUPPORTED_BEDROCK_SERVER_TOOL_PREFIX)
+            }
+        )
+        if not unsupported:
+            return
+        raise litellm.BadRequestError(
+            message=(
+                f"Amazon Bedrock does not support the Anthropic server tool(s) {unsupported}. "
+                "Enable LiteLLM's web-search interception to serve them, by adding "
+                '`websearch_interception` to `litellm_settings.callbacks`, listing "bedrock" under '
+                "`litellm_settings.websearch_interception_params.enabled_providers`, and declaring a "
+                "`search_tools` entry. Otherwise remove the tool from the request."
+            ),
+            model=model,
+            llm_provider="bedrock",
+        )
+
     def transform_anthropic_messages_request(
         self,
         model: str,
@@ -626,6 +662,8 @@ class AmazonAnthropicClaudeMessagesConfig(
             headers=headers,
         )
         self._normalize_system_role_messages(anthropic_messages_request, model=model)
+        request_view: Final = cast(Mapping[str, object], anthropic_messages_request)  # cast-ok: body is untyped here
+        self._reject_unsupported_server_tools(request_view, model=model)
         #########################################################
         ############## BEDROCK Invoke SPECIFIC TRANSFORMATION ###
         #########################################################

tests/test_litellm/llms/bedrock/messages/invoke_transformations/test_anthropic_claude3_transformation.py

@@ -29,6 +29,8 @@ from litellm.llms.bedrock.messages.invoke_transformations.anthropic_claude3_tran
     AmazonAnthropicClaudeMessagesConfig,
     AmazonAnthropicClaudeMessagesStreamDecoder,
 )
+import litellm
+from litellm.types.router import GenericLiteLLMParams
 
 
 @pytest.fixture
@@ -2580,3 +2582,50 @@ def test_replayed_intercepted_search_turn_leaves_no_unsupported_block_for_bedroc
     assert "server_tool_use" not in serialized
     assert expected_evidence in serialized
     assert "Rome was founded in 753 BC." in serialized
+
+
+def test_bedrock_messages_rejects_anthropic_web_search_server_tool():
+    """Bedrock hosts none of Anthropic's web_search server tools. Forwarding one
+    earns an opaque 'The provided request is not valid' from AWS that names
+    neither the tool nor a way forward, so reject it here with a message that
+    does both."""
+    with pytest.raises(litellm.BadRequestError) as excinfo:
+        AmazonAnthropicClaudeMessagesConfig().transform_anthropic_messages_request(
+            model="us.anthropic.claude-haiku-4-5-20251001-v1:0",
+            messages=[{"role": "user", "content": "Anthropic Claude news"}],
+            anthropic_messages_optional_request_params={
+                "max_tokens": 64,
+                "tools": [{"type": "web_search_20250305", "name": "web_search", "max_uses": 3}],
+            },
+            litellm_params=GenericLiteLLMParams(),
+            headers={},
+        )
+
+    message = str(excinfo.value)
+    assert "web_search_20250305" in message
+    assert "websearch_interception" in message
+
+
+def test_bedrock_messages_allows_the_tool_interception_rewrites_it_into():
+    """Web-search interception rewrites the native tool into LiteLLM's own search
+    tool before this transform runs, and that rewritten tool carries an
+    input_schema like any custom tool. Rejecting the native type must not touch
+    it, or enabling interception would break the very path that serves search."""
+    body = AmazonAnthropicClaudeMessagesConfig().transform_anthropic_messages_request(
+        model="us.anthropic.claude-haiku-4-5-20251001-v1:0",
+        messages=[{"role": "user", "content": "Anthropic Claude news"}],
+        anthropic_messages_optional_request_params={
+            "max_tokens": 64,
+            "tools": [
+                {
+                    "name": "litellm_web_search",
+                    "description": "Search the web",
+                    "input_schema": {"type": "object", "properties": {"query": {"type": "string"}}},
+                }
+            ],
+        },
+        litellm_params=GenericLiteLLMParams(),
+        headers={},
+    )
+
+    assert [tool["name"] for tool in body["tools"]] == ["litellm_web_search"]