From d47268939d1e936aa6c64d67e514ac8607366ce4 Mon Sep 17 00:00:00 2001
From: Filippo Menghi <113345637+Cyberfilo@users.noreply.github.com>
Date: Wed, 10 Jun 2026 12:43:28 +0200
Subject: [PATCH] fix(mcp): coerce mcp_server_cost_info values to float at
 ingest (#30109)

* fix(mcp): coerce mcp_server_cost_info values to float at ingest

YAML 1.1 parses scientific notation without a decimal point
(e.g. 7e-05) as a string, and MCPServerCostInfo is a TypedDict with no
runtime validation, so a string-typed default_cost_per_query from
config.yaml flowed through the proxy untouched and crashed the MCP
server settings page with '.toFixed is not a function'. Normalize
mcp_server_cost_info on both the config and DB load paths, dropping
non-numeric values with a warning instead of failing the server load.

Fixes #27097.

* fix(mcp): drop non-numeric default_cost_per_query instead of nulling it

Keeping the key with a None value still exposes a null to the UI,
which can crash .toFixed formatting when the consumer checks key
existence rather than truthiness. Delete the key on coercion failure,
matching how non-numeric per-tool cost entries are already omitted.
---
 .../mcp_server/mcp_server_manager.py          | 48 ++++++++++++++
 .../mcp_server/test_mcp_server_manager.py     | 64 +++++++++++++++++++
 2 files changed, 112 insertions(+)

diff --git a/litellm/proxy/_experimental/mcp_server/mcp_server_manager.py b/litellm/proxy/_experimental/mcp_server/mcp_server_manager.py
index 85ac6b399f4..73935beeb3a 100644
--- a/litellm/proxy/_experimental/mcp_server/mcp_server_manager.py
+++ b/litellm/proxy/_experimental/mcp_server/mcp_server_manager.py
@@ -354,6 +354,52 @@ def _deserialize_json_list(data: Any) -> Optional[List[Dict[str, Any]]]:
     ]
 
 
+def _normalize_mcp_server_cost_info(mcp_info: MCPInfo) -> None:
+    """Coerce ``mcp_server_cost_info`` numeric fields to ``float`` at ingest.
+
+    YAML 1.1 parses scientific notation without a decimal point (e.g.
+    ``7e-05``) as a string, and ``MCPServerCostInfo`` is a TypedDict with no
+    runtime validation, so string-typed costs flow through to the UI and
+    crash its ``.toFixed`` formatting. Values that cannot be coerced are
+    dropped with a warning instead of failing the server load.
+    """
+    cost_info = mcp_info.get("mcp_server_cost_info")
+    if not isinstance(cost_info, dict):
+        return
+
+    server_name = mcp_info.get("server_name")
+    normalized = dict(cost_info)
+
+    default_cost = normalized.get("default_cost_per_query")
+    if default_cost is not None:
+        try:
+            normalized["default_cost_per_query"] = float(default_cost)
+        except (TypeError, ValueError):
+            verbose_logger.warning(
+                "MCP server '%s' has non-numeric default_cost_per_query %r; ignoring it",
+                server_name,
+                default_cost,
+            )
+            del normalized["default_cost_per_query"]
+
+    tool_costs = normalized.get("tool_name_to_cost_per_query")
+    if isinstance(tool_costs, dict):
+        normalized_tool_costs = {}
+        for tool_name, cost in tool_costs.items():
+            try:
+                normalized_tool_costs[tool_name] = float(cost)
+            except (TypeError, ValueError):
+                verbose_logger.warning(
+                    "MCP server '%s' has non-numeric cost %r for tool '%s'; ignoring it",
+                    server_name,
+                    cost,
+                    tool_name,
+                )
+        normalized["tool_name_to_cost_per_query"] = normalized_tool_costs
+
+    mcp_info["mcp_server_cost_info"] = normalized
+
+
 def _create_sampling_callback(user_api_key_auth: Optional[Any] = None):
     """
     Create a sampling callback for MCP ClientSession.
@@ -621,6 +667,7 @@ class MCPServerManager:
                 mcp_info["server_name"] = server_name
             if "description" not in mcp_info and server_config.get("description"):
                 mcp_info["description"] = server_config.get("description")
+            _normalize_mcp_server_cost_info(mcp_info)
 
             # Use alias for name if present, else server_name
             alias = server_config.get("alias", None)
@@ -1091,6 +1138,7 @@ class MCPServerManager:
             mcp_info["server_name"] = mcp_server.server_name or mcp_server.server_id
         if "description" not in mcp_info and mcp_server.description:
             mcp_info["description"] = mcp_server.description
+        _normalize_mcp_server_cost_info(mcp_info)
 
         auth_type = cast(MCPAuthType, mcp_server.auth_type)
         server_url = mcp_server.url
diff --git a/tests/test_litellm/proxy/_experimental/mcp_server/test_mcp_server_manager.py b/tests/test_litellm/proxy/_experimental/mcp_server/test_mcp_server_manager.py
index 48c09f6e456..1b815b7a1c9 100644
--- a/tests/test_litellm/proxy/_experimental/mcp_server/test_mcp_server_manager.py
+++ b/tests/test_litellm/proxy/_experimental/mcp_server/test_mcp_server_manager.py
@@ -30,6 +30,7 @@ from litellm.proxy._experimental.mcp_server.mcp_server_manager import (
     MCPServerManager,
     _deserialize_json_dict,
     _deserialize_json_list,
+    _normalize_mcp_server_cost_info,
 )
 from litellm.proxy._types import (
     LiteLLM_MCPServerTable,
@@ -257,6 +258,69 @@ class TestMCPServerManager:
         assert server.alias == "friendly_alias"
         assert server.server_name == "validserver"
 
+    @pytest.mark.asyncio
+    async def test_load_servers_from_config_coerces_cost_string_to_float(self):
+        """YAML 1.1 parses `7e-05` as a string; ingest must coerce it to float."""
+        manager = MCPServerManager()
+        config = {
+            "google_maps": {
+                "url": "https://example.com/mcp",
+                "transport": MCPTransport.http,
+                "mcp_info": {
+                    "mcp_server_cost_info": {
+                        "default_cost_per_query": "7e-05",
+                        "tool_name_to_cost_per_query": {"geocode": "1e-3"},
+                    }
+                },
+            }
+        }
+
+        await manager.load_servers_from_config(config)
+
+        server = next(iter(manager.config_mcp_servers.values()))
+        cost_info = server.mcp_info["mcp_server_cost_info"]
+        assert cost_info["default_cost_per_query"] == 7e-05
+        assert isinstance(cost_info["default_cost_per_query"], float)
+        assert cost_info["tool_name_to_cost_per_query"]["geocode"] == 1e-3
+        assert isinstance(cost_info["tool_name_to_cost_per_query"]["geocode"], float)
+
+    def test_normalize_mcp_server_cost_info_preserves_float_values(self):
+        mcp_info = {
+            "server_name": "maps",
+            "mcp_server_cost_info": {
+                "default_cost_per_query": 0.01,
+                "tool_name_to_cost_per_query": {"search": 0.05},
+            },
+        }
+
+        _normalize_mcp_server_cost_info(mcp_info)
+
+        cost_info = mcp_info["mcp_server_cost_info"]
+        assert cost_info["default_cost_per_query"] == 0.01
+        assert cost_info["tool_name_to_cost_per_query"] == {"search": 0.05}
+
+    def test_normalize_mcp_server_cost_info_drops_non_numeric_values(self):
+        mcp_info = {
+            "server_name": "maps",
+            "mcp_server_cost_info": {
+                "default_cost_per_query": "not-a-number",
+                "tool_name_to_cost_per_query": {"search": "free", "geocode": "2e-4"},
+            },
+        }
+
+        _normalize_mcp_server_cost_info(mcp_info)
+
+        cost_info = mcp_info["mcp_server_cost_info"]
+        assert "default_cost_per_query" not in cost_info
+        assert cost_info["tool_name_to_cost_per_query"] == {"geocode": 2e-4}
+
+    def test_normalize_mcp_server_cost_info_leaves_missing_cost_info_alone(self):
+        mcp_info = {"server_name": "maps"}
+
+        _normalize_mcp_server_cost_info(mcp_info)
+
+        assert "mcp_server_cost_info" not in mcp_info
+
     def test_warns_when_custom_separator_invalid(self, monkeypatch, caplog):
         """Invalid MCP_TOOL_PREFIX_SEPARATOR values should log a warning."""