From c45500604471142a47b87b016ae29119e4fc8211 Mon Sep 17 00:00:00 2001
From: syf2211 <syf2211@users.noreply.github.com>
Date: Sun, 28 Jun 2026 10:05:55 +0000
Subject: [PATCH] fix(smolagents): support MCP tools with no input parameters

Parameter-less tools may expose a valid JSON Schema of {"type": "object"}
without a properties field. SmolAgentsAdapter previously assumed properties
was always present and raised KeyError during adaptation.

Fixes #78
---
 src/mcpadapt/smolagents_adapter.py | 11 +++++++----
 tests/test_smolagents_adapter.py   | 27 +++++++++++++++++++++++++++
 2 files changed, 34 insertions(+), 4 deletions(-)

diff --git a/src/mcpadapt/smolagents_adapter.py b/src/mcpadapt/smolagents_adapter.py
index d48b542..e2d6935 100644
--- a/src/mcpadapt/smolagents_adapter.py
+++ b/src/mcpadapt/smolagents_adapter.py
@@ -99,12 +99,15 @@ def adapt(
             if k != "$defs"
         }
 
+        # Parameter-less tools may omit `properties`; treat that as an empty object schema.
+        properties = input_schema.setdefault("properties", {})
+
         # make sure mandatory `description` and `type` is provided for each arguments:
-        for k, v in input_schema["properties"].items():
+        for k, v in properties.items():
             if "description" not in v:
-                input_schema["properties"][k]["description"] = "see tool description"
+                properties[k]["description"] = "see tool description"
             if "type" not in v:
-                input_schema["properties"][k]["type"] = "string"
+                properties[k]["type"] = "string"
 
         # Extract and resolve outputSchema if present (only if structured_output=True)
         output_schema = None
@@ -235,7 +238,7 @@ def forward(
         tool = MCPAdaptTool(
             name=mcp_tool.name,
             description=mcp_tool.description or "",
-            inputs=input_schema["properties"],
+            inputs=properties,
             output_type=output_type,
             output_schema=output_schema,
             structured_output=self.structured_output,
diff --git a/tests/test_smolagents_adapter.py b/tests/test_smolagents_adapter.py
index a1ccb2b..3824af7 100644
--- a/tests/test_smolagents_adapter.py
+++ b/tests/test_smolagents_adapter.py
@@ -135,6 +135,33 @@ def test_optional_sync(echo_server_optional_script):
         assert tools[2](text="hello") == "Echo: hello"
 
 
+def test_tool_with_no_input_parameters():
+    mcp_server_script = dedent(
+        '''
+        from mcp.server.fastmcp import FastMCP
+
+        mcp = FastMCP("Version Server")
+
+        @mcp.tool()
+        def server_version() -> str:
+            """Return the server version."""
+            return "1.0.0"
+
+        mcp.run()
+        '''
+    )
+    with MCPAdapt(
+        StdioServerParameters(
+            command="uv", args=["run", "python", "-c", mcp_server_script]
+        ),
+        SmolAgentsAdapter(),
+    ) as tools:
+        assert len(tools) == 1
+        assert tools[0].name == "server_version"
+        assert tools[0].inputs == {}
+        assert tools[0]() == "1.0.0"
+
+
 def test_tool_name_with_dashes():
     mcp_server_script = dedent(
         '''