diff --git a/litellm/integrations/websearch_interception/handler.py b/litellm/integrations/websearch_interception/handler.py
index 2394ae4a43b..470a0c03a0d 100644
--- a/litellm/integrations/websearch_interception/handler.py
+++ b/litellm/integrations/websearch_interception/handler.py
@@ -11,6 +11,7 @@ import math
 import uuid
 from collections.abc import AsyncIterator, Mapping, Sequence
 from dataclasses import dataclass
+from itertools import chain
 from types import MappingProxyType
 from typing import TYPE_CHECKING, Any, Final, Literal, TypedDict, TypeVar, cast
 
@@ -103,9 +104,16 @@ _RESPONSE_CONTENT_FIELD: Final = "content"
 _ResponseT: Final = TypeVar("_ResponseT")
 
 
+def _web_search_domain_strings(tool: Mapping[str, object], key: str) -> tuple[str, ...]:
+    value = tool.get(key)
+    if not isinstance(value, list):
+        return ()
+    return tuple(item for item in value if isinstance(item, str) and item)
+
+
 def _extract_web_search_domain_filters(
     tools: Sequence[dict[str, object]],
-) -> dict[str, list[str]] | None:
+) -> Mapping[str, tuple[str, ...]] | None:
     """Collect ``allowed_domains`` / ``blocked_domains`` from web search tools.
 
     Anthropic-native ``web_search_*`` tools carry optional domain limits. The
@@ -116,23 +124,20 @@ def _extract_web_search_domain_filters(
 
     Returns None when no web search tool carries a domain limit.
     """
-    allowed: list[str] = []
-    blocked: list[str] = []
-    for tool in tools:
-        if not is_web_search_tool(tool):
-            continue
-        for key, bucket in (("allowed_domains", allowed), ("blocked_domains", blocked)):
-            value = tool.get(key)
-            if isinstance(value, list):
-                bucket.extend(item for item in value if isinstance(item, str) and item)
+    web_tools: Final = tuple(tool for tool in tools if is_web_search_tool(tool))
+    allowed: Final = tuple(
+        chain.from_iterable(_web_search_domain_strings(tool, "allowed_domains") for tool in web_tools)
+    )
+    blocked: Final = tuple(
+        chain.from_iterable(_web_search_domain_strings(tool, "blocked_domains") for tool in web_tools)
+    )
     if not allowed and not blocked:
         return None
-    domain_filters: dict[str, list[str]] = {}
-    if allowed:
-        domain_filters["allowed_domains"] = allowed
-    if blocked:
-        domain_filters["blocked_domains"] = blocked
-    return domain_filters
+    if not blocked:
+        return MappingProxyType({"allowed_domains": allowed})
+    if not allowed:
+        return MappingProxyType({"blocked_domains": blocked})
+    return MappingProxyType({"allowed_domains": allowed, "blocked_domains": blocked})
 
 
 class _PlanMetadataView(TypedDict):
@@ -1658,18 +1663,19 @@ class WebSearchInterceptionLogger(CustomLogger):
             # allowlist and ``blocked_domains`` as '-'-prefixed exclusions —
             # the convention litellm.asearch()'s providers (e.g. Perplexity)
             # use for search_domain_filter.
-            search_domain_filter: list[str] | None = None
             request_domain_filters: Final = kwargs.get(WEBSEARCH_DOMAIN_FILTER_KEY) if kwargs is not None else None
-            if isinstance(request_domain_filters, dict):
-                allowed: Final[list[str]] = [
-                    item for item in request_domain_filters.get("allowed_domains", []) if isinstance(item, str) and item
-                ]
-                blocked: Final[list[str]] = [
-                    item for item in request_domain_filters.get("blocked_domains", []) if isinstance(item, str) and item
-                ]
-                if allowed or blocked:
-                    search_domain_filter = allowed + [f"-{item}" for item in blocked]
-                    verbose_logger.debug("WebSearchInterception: Applying domain filter %s", search_domain_filter)
+            domain_view: Final = (
+                request_domain_filters if isinstance(request_domain_filters, Mapping) else MappingProxyType({})
+            )
+            allowed: Final = tuple(
+                item for item in domain_view.get("allowed_domains", ()) if isinstance(item, str) and item
+            )
+            blocked: Final = tuple(
+                f"-{item}" for item in domain_view.get("blocked_domains", ()) if isinstance(item, str) and item
+            )
+            search_domain_filter: Final = [*allowed, *blocked] or None  # mutable-ok: JSON request array, not mutated
+            if search_domain_filter is not None:
+                verbose_logger.debug("WebSearchInterception: Applying domain filter %s", search_domain_filter)
             search_kwargs: Final = MappingProxyType(
                 {**configured_search_kwargs, **parent_correlation.as_search_kwargs()}
             )
diff --git a/tests/unit/integrations/websearch_interception/test_websearch_domain_filters.py b/tests/unit/integrations/websearch_interception/test_websearch_domain_filters.py
index 70a082f83a3..2cbffab71a9 100644
--- a/tests/unit/integrations/websearch_interception/test_websearch_domain_filters.py
+++ b/tests/unit/integrations/websearch_interception/test_websearch_domain_filters.py
@@ -43,8 +43,8 @@ class TestExtractWebSearchDomainFilters:
             }
         ]
         assert _extract_web_search_domain_filters(tools) == {
-            "allowed_domains": ["docs.litellm.ai"],
-            "blocked_domains": ["twitter.com", "x.com"],
+            "allowed_domains": ("docs.litellm.ai",),
+            "blocked_domains": ("twitter.com", "x.com"),
         }
 
     def test_returns_none_without_domain_limits(self):
@@ -65,7 +65,7 @@ class TestExtractWebSearchDomainFilters:
                 "allowed_domains": ["docs.litellm.ai", 42, None],
             }
         ]
-        assert _extract_web_search_domain_filters(tools) == {"allowed_domains": ["docs.litellm.ai"]}
+        assert _extract_web_search_domain_filters(tools) == {"allowed_domains": ("docs.litellm.ai",)}
 
 
 class TestDeploymentHookStashesDomainFilters:
@@ -86,8 +86,8 @@ class TestDeploymentHookStashesDomainFilters:
         out = await logger.async_pre_call_deployment_hook(kwargs, None)
         assert out is not None
         assert kwargs[WEBSEARCH_DOMAIN_FILTER_KEY] == {
-            "allowed_domains": ["docs.litellm.ai"],
-            "blocked_domains": ["twitter.com"],
+            "allowed_domains": ("docs.litellm.ai",),
+            "blocked_domains": ("twitter.com",),
         }
 
     @pytest.mark.asyncio