diff --git a/astrbot/core/provider/sources/anthropic_source.py b/astrbot/core/provider/sources/anthropic_source.py
index 7e2e09f91..cd6262faa 100644
--- a/astrbot/core/provider/sources/anthropic_source.py
+++ b/astrbot/core/provider/sources/anthropic_source.py
@@ -665,10 +665,15 @@ class ProviderAnthropic(Provider):
                         )
                     elif event.content_block.type == "tool_use":
                         # 工具使用块开始，初始化缓冲区
+                        # Keep the input from the start event; streamed deltas
+                        # replace it only when they carry JSON.
+                        start_input = event.content_block.input
                         tool_use_buffer[event.index] = {
                             "id": event.content_block.id,
                             "name": event.content_block.name,
-                            "input": {},
+                            "input": start_input
+                            if isinstance(start_input, dict)
+                            else {},
                         }
 
                 elif event.type == "content_block_delta":
@@ -713,7 +718,8 @@ class ProviderAnthropic(Provider):
                         # 解析完整的工具调用
                         tool_info = tool_use_buffer[event.index]
                         try:
-                            if "input_json" in tool_info:
+                            # 无参数的工具只会收到一个空的 partial_json
+                            if tool_info.get("input_json"):
                                 tool_info["input"] = json.loads(tool_info["input_json"])
 
                             # 添加到最终结果
diff --git a/tests/test_anthropic_source.py b/tests/test_anthropic_source.py
index 4aa0f2efb..2b283be08 100644
--- a/tests/test_anthropic_source.py
+++ b/tests/test_anthropic_source.py
@@ -1,8 +1,18 @@
+import json
+
+import pytest
+from anthropic import _base_client as anthropic_base_client
 from anthropic.types import MessageDeltaUsage, Usage
 
+from astrbot.core.agent.tool import FunctionTool, ToolSet
 from astrbot.core.provider.entities import TokenUsage
 from astrbot.core.provider.sources.anthropic_source import ProviderAnthropic
 
+# The SDK bundles its own httpx (``httpx`` before 1.0.0, ``httpx2`` after).
+sdk_httpx = getattr(
+    anthropic_base_client, "httpx", getattr(anthropic_base_client, "httpx2", None)
+)
+
 
 def _provider() -> ProviderAnthropic:
     return ProviderAnthropic.__new__(ProviderAnthropic)
@@ -75,3 +85,114 @@ def test_anthropic_update_usage_omitted_fields_are_preserved():
     assert token_usage.input_other == 5
     assert token_usage.input_cached == 0
     assert token_usage.output == 7
+
+
+def _tool_use_stream(
+    partial_json_chunks: list[str], start_input: dict | None = None
+) -> bytes:
+    events = [
+        {
+            "type": "message_start",
+            "message": {
+                "id": "msg_1",
+                "type": "message",
+                "role": "assistant",
+                "model": "claude-test",
+                "content": [],
+                "stop_reason": None,
+                "stop_sequence": None,
+                "usage": {"input_tokens": 10, "output_tokens": 1},
+            },
+        },
+        {
+            "type": "content_block_start",
+            "index": 0,
+            "content_block": {
+                "type": "tool_use",
+                "id": "toolu_01",
+                "name": "get_time",
+                "input": start_input or {},
+            },
+        },
+        *(
+            {
+                "type": "content_block_delta",
+                "index": 0,
+                "delta": {"type": "input_json_delta", "partial_json": chunk},
+            }
+            for chunk in partial_json_chunks
+        ),
+        {"type": "content_block_stop", "index": 0},
+        {
+            "type": "message_delta",
+            "delta": {"stop_reason": "tool_use", "stop_sequence": None},
+            "usage": {"output_tokens": 5},
+        },
+        {"type": "message_stop"},
+    ]
+    return "".join(
+        f"event: {event['type']}\ndata: {json.dumps(event)}\n\n" for event in events
+    ).encode()
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize(
+    ("chunks", "start_input", "expected_args"),
+    [
+        ([""], None, {}),
+        ([], None, {}),
+        (["", '{"tz": "UTC"}'], None, {"tz": "UTC"}),
+        ([], {"tz": "UTC"}, {"tz": "UTC"}),
+    ],
+)
+async def test_anthropic_stream_keeps_tool_call_with_empty_input(
+    monkeypatch, chunks, start_input, expected_args
+):
+    body = _tool_use_stream(chunks, start_input)
+    transport = sdk_httpx.MockTransport(
+        lambda request: sdk_httpx.Response(
+            200, headers={"content-type": "text/event-stream"}, content=body
+        )
+    )
+    monkeypatch.setattr(
+        ProviderAnthropic,
+        "_create_http_client",
+        lambda self, provider_config: sdk_httpx.AsyncClient(transport=transport),
+    )
+    provider = ProviderAnthropic(
+        {
+            "id": "test",
+            "type": "anthropic_chat_completion",
+            "key": ["sk-test"],
+            "model": "claude-test",
+            "api_base": "https://api.anthropic.test",
+        },
+        {},
+    )
+    tools = ToolSet(
+        [
+            FunctionTool(
+                name="get_time",
+                description="Return the current time.",
+                parameters={"type": "object", "properties": {}},
+            )
+        ]
+    )
+    payloads = {
+        "messages": [{"role": "user", "content": "what time is it?"}],
+        "model": "claude-test",
+    }
+
+    try:
+        responses = [r async for r in provider._query_stream(payloads, tools)]
+    finally:
+        await provider.terminate()
+
+    tool_chunks = [r for r in responses if r.role == "tool"]
+    assert len(tool_chunks) == 1
+    final = responses[-1]
+    assert not final.is_chunk
+    for response in (tool_chunks[0], final):
+        assert response.tools_call_name == ["get_time"]
+        assert response.tools_call_args == [expected_args]
+        assert response.tools_call_ids == ["toolu_01"]