diff --git a/slime/agent/adapters/anthropic.py b/slime/agent/adapters/anthropic.py
index 0a48b09fd5..380d910069 100644
--- a/slime/agent/adapters/anthropic.py
+++ b/slime/agent/adapters/anthropic.py
@@ -36,6 +36,11 @@ class -> translation -> reply building -> request framing) is shared between
 logger = logging.getLogger(__name__)
 
 
+def _representable_tool_uses(tool_uses: list[dict[str, Any]]) -> list[dict[str, Any]]:
+    """Keep only calls whose arguments can be represented as an input object."""
+    return [tu for tu in tool_uses if tu.get("arguments_valid", isinstance(tu.get("input"), dict))]
+
+
 class AnthropicAdapter(BaseAdapter):
     """Anthropic Messages-compatible HTTP adapter: wire translation and reply
     framing only; the turn machinery is inherited from BaseAdapter."""
@@ -64,7 +69,7 @@ def _build_reply(self, parsed, raw_finish, translated, tools_schema) -> Reply:
         blocks, stop_reason, manager_message = _build_reply_parts(parsed, raw_finish)
         return Reply(
             manager_message=manager_message,
-            finish_reason=manager_finish_reason(parsed.tool_uses, raw_finish),
+            finish_reason=manager_finish_reason(_representable_tool_uses(parsed.tool_uses), raw_finish),
             wire=(blocks, stop_reason),
         )
 
@@ -160,8 +165,9 @@ def _build_reply_parts(
     if parsed.text:
         blocks.append({"type": "text", "text": parsed.text})
 
+    representable_tool_uses = _representable_tool_uses(parsed.tool_uses)
     manager_tcs: list[dict] = []
-    for tu in parsed.tool_uses:
+    for tu in representable_tool_uses:
         tu_id = f"toolu_{secrets.token_hex(8)}"
         blocks.append({"type": "tool_use", "id": tu_id, "name": tu["name"], "input": tu["input"]})
         # tu_id is wire-only; tool_call_dict drops it so the leaf matches its echo
@@ -170,7 +176,7 @@ def _build_reply_parts(
     if not blocks:
         blocks.append({"type": "text", "text": ""})
 
-    if parsed.tool_uses:
+    if representable_tool_uses:
         stop_reason = "tool_use"
     elif finish == "length":
         stop_reason = "max_tokens"
diff --git a/slime/agent/adapters/openai.py b/slime/agent/adapters/openai.py
index ad3d2e4d87..9f652eb1ad 100644
--- a/slime/agent/adapters/openai.py
+++ b/slime/agent/adapters/openai.py
@@ -226,6 +226,12 @@ def _build_reply_parts(parsed: ParsedModelOutput, finish: str) -> tuple[dict[str
         args_dict = tu.get("input") or {}
         if not isinstance(args_dict, dict):
             args_dict = {"_raw_arguments": str(args_dict)}
+        raw_arguments = tu.get("raw_arguments")
+        wire_arguments = (
+            raw_arguments
+            if isinstance(raw_arguments, str)
+            else json.dumps(args_dict, ensure_ascii=False, sort_keys=True)
+        )
         call_id = f"call_{secrets.token_hex(12)}"
         wire_tool_calls.append(
             {
@@ -233,7 +239,7 @@ def _build_reply_parts(parsed: ParsedModelOutput, finish: str) -> tuple[dict[str
                 "type": "function",
                 "function": {
                     "name": name,
-                    "arguments": json.dumps(args_dict, ensure_ascii=False, sort_keys=True),
+                    "arguments": wire_arguments,
                 },
             }
         )
diff --git a/slime/agent/parsing.py b/slime/agent/parsing.py
index 56bc85a4bc..abcd4014e4 100644
--- a/slime/agent/parsing.py
+++ b/slime/agent/parsing.py
@@ -22,6 +22,18 @@ class ParsedModelOutput:
     ill_formed: bool = False
 
 
+def _parse_tool_arguments(raw_arguments: str | None) -> tuple[dict[str, Any], str, bool]:
+    """Return canonical mapping, original wire text, and object validity."""
+    raw = raw_arguments if raw_arguments is not None else "{}"
+    try:
+        parsed = json.loads(raw)
+    except json.JSONDecodeError:
+        return {"_raw_arguments": raw}, raw, False
+    if not isinstance(parsed, dict):
+        return {"_raw_arguments": raw}, raw, False
+    return parsed, raw, True
+
+
 def parse_model_output(
     raw_output: str,
     *,
@@ -77,12 +89,17 @@ def parse_tool_uses(
             except Exception:
                 logger.exception("[agent.parsing] sglang tool-call parsing failed; falling back")
         for c in calls:
-            try:
-                args = json.loads(c.parameters or "{}")
-            except json.JSONDecodeError:
-                args = {"_raw_arguments": c.parameters}
+            args, raw_arguments, arguments_valid = _parse_tool_arguments(c.parameters)
+            if not arguments_valid:
                 ill_formed = True
-            tool_uses.append({"name": c.name or "tool", "input": args})
+            tool_uses.append(
+                {
+                    "name": c.name or "tool",
+                    "input": args,
+                    "raw_arguments": raw_arguments,
+                    "arguments_valid": arguments_valid,
+                }
+            )
 
     if not tool_uses and tools_schema:
         body_text, tool_uses = parse_xml_tool_uses(body_text, tools_schema)
diff --git a/tests/test_agent/test_adapters.py b/tests/test_agent/test_adapters.py
index 852a9cf973..e4c98d09c3 100644
--- a/tests/test_agent/test_adapters.py
+++ b/tests/test_agent/test_adapters.py
@@ -28,7 +28,12 @@
 from tests.test_agent._fakes import FakeSGLangServer, FakeTokenizer  # noqa: E402
 
 from slime.agent.adapters import anthropic, openai  # noqa: E402
-from slime.agent.parsing import parse_model_output, parse_xml_tool_uses  # noqa: E402
+from slime.agent.parsing import (  # noqa: E402
+    ParsedModelOutput,
+    _parse_tool_arguments,
+    parse_model_output,
+    parse_xml_tool_uses,
+)
 from slime.utils.types import Sample  # noqa: E402
 
 NUM_GPUS = 0
@@ -160,6 +165,52 @@ def test_openai_translation_developer_to_system_and_tool_calls_to_dict():
     ]
 
 
+def test_openai_reply_preserves_raw_tool_arguments():
+    raw = '{"cmd": "pytest"'
+    parsed = ParsedModelOutput(
+        reasoning="",
+        text="",
+        tool_uses=[
+            {
+                "name": "bash",
+                "input": {"_raw_arguments": raw},
+                "raw_arguments": raw,
+                "arguments_valid": False,
+            }
+        ],
+        ill_formed=True,
+    )
+
+    wire, manager, finish = openai._build_reply_parts(parsed, "stop")
+
+    assert wire["tool_calls"][0]["function"]["arguments"] == raw
+    assert manager["tool_calls"][0]["function"]["arguments"] == {"_raw_arguments": raw}
+    assert finish == "tool_calls"
+
+
+def test_anthropic_reply_drops_unrepresentable_tool_arguments():
+    raw = '{"cmd": "pytest"'
+    parsed = ParsedModelOutput(
+        reasoning="",
+        text="",
+        tool_uses=[
+            {
+                "name": "bash",
+                "input": {"_raw_arguments": raw},
+                "raw_arguments": raw,
+                "arguments_valid": False,
+            }
+        ],
+        ill_formed=True,
+    )
+
+    blocks, stop_reason, manager = anthropic._build_reply_parts(parsed, "stop")
+
+    assert blocks == [{"type": "text", "text": ""}]
+    assert stop_reason == "end_turn"
+    assert manager == {"role": "assistant", "content": ""}
+
+
 # ===========================================================================
 # §3 non-stream JSON + token capture (real HTTP, real /generate)
 # ===========================================================================
@@ -430,6 +481,23 @@ def test_parse_model_output_plain_text_no_parsers():
     assert parsed.reasoning == ""
 
 
+@pytest.mark.parametrize(
+    ("raw", "expected", "valid"),
+    [
+        (' {"q" : "slime"} ', {"q": "slime"}, True),
+        ('{"cmd": "pytest"', {"_raw_arguments": '{"cmd": "pytest"'}, False),
+        ('["not", "an", "object"]', {"_raw_arguments": '["not", "an", "object"]'}, False),
+        (None, {}, True),
+    ],
+)
+def test_parse_tool_arguments_preserves_wire_text(raw, expected, valid):
+    parsed, wire_text, is_valid = _parse_tool_arguments(raw)
+
+    assert parsed == expected
+    assert wire_text == (raw if raw is not None else "{}")
+    assert is_valid is valid
+
+
 def test_parse_model_output_think_split_fallback():
     # The qwen3 reasoning parser lives in sglang (lazy import); skip where the
     # lean CPU CI env has no sglang installed.