diff --git a/astrbot/core/tools/message_tools.py b/astrbot/core/tools/message_tools.py
index c3f33a7e8b..018933d0ea 100644
--- a/astrbot/core/tools/message_tools.py
+++ b/astrbot/core/tools/message_tools.py
@@ -132,6 +132,14 @@ async def call(
             ):
                 return permission_error
         messages = kwargs.get("messages")
+        # Some LLMs (e.g. MiniMax) may serialize the array value as a JSON string
+        # when the text contains newlines. Try to recover.
+        # https://github.com/AstrBotDevs/AstrBot/issues/7961
+        if isinstance(messages, str):
+            try:
+                messages = json.loads(messages)
+            except json.JSONDecodeError:
+                pass
         if not isinstance(messages, list) or not messages:
             return "error: messages parameter is empty or invalid."
 
diff --git a/tests/unit/test_message_tools.py b/tests/unit/test_message_tools.py
index eedee80abb..3e30cbcec7 100644
--- a/tests/unit/test_message_tools.py
+++ b/tests/unit/test_message_tools.py
@@ -1,5 +1,6 @@
 """Tests for send_message_to_user session handling."""
 
+import json
 from types import SimpleNamespace
 from unittest.mock import AsyncMock
 
@@ -133,3 +134,43 @@ async def test_send_message_empty_messages_returns_error():
     result = await tool.call(ctx, messages=[], session="oc_xxx")
     assert "error:" in result
     assert "messages" in result.lower()
+
+
+# JSON-string messages compatibility for issue #7961.
+
+
+@pytest.mark.asyncio
+async def test_messages_as_json_string_parsed():
+    """JSON-string array messages are parsed before validation."""
+    tool = SendMessageToUserTool()
+    ctx = _make_context(current_session="feishu:GroupMessage:oc_xxx")
+    messages_str = '[{"type": "plain", "text": "hello from string"}]'
+    result = await tool.call(ctx, messages=messages_str, session="oc_xxx")
+    assert "Message sent to session" in result
+
+
+@pytest.mark.asyncio
+async def test_messages_as_json_string_with_newlines():
+    """JSON-string messages preserve multiline text after parsing."""
+    tool = SendMessageToUserTool()
+    ctx = _make_context(current_session="feishu:GroupMessage:oc_xxx")
+
+    long_text = "line1\n\nline2\nline3"
+    messages_str = json.dumps([{"type": "plain", "text": long_text}])
+    result = await tool.call(ctx, messages=messages_str, session="oc_xxx")
+    assert "Message sent to session" in result
+    call_args = ctx.context.context.send_message.call_args
+    chain = call_args[0][1]
+    assert len(chain.chain) == 1
+    assert chain.chain[0].text == long_text
+
+
+@pytest.mark.asyncio
+async def test_messages_as_invalid_json_string_returns_error():
+    """Invalid JSON-string messages still return a validation error."""
+    tool = SendMessageToUserTool()
+    ctx = _make_context()
+    result = await tool.call(ctx, messages="not valid json at all", session="oc_xxx")
+    assert "error:" in result or "invalid" in result.lower()
+    result2 = await tool.call(ctx, messages="", session="oc_xxx")
+    assert "error:" in result2 or "invalid" in result2.lower()