fix(mcp-adaptors): langchain-mcp-adapter not working with tools without parameters

libs/langchain-mcp-adapters/__tests__/tools.test.ts

@@ -130,6 +130,56 @@ describe("Simplified Tool Adapter Tests", () => {
       });
     });
 
+    test("should load tool with no input parameters", async () => {
+      // Set up mock response
+      mockClient.listTools.mockReturnValueOnce(
+        Promise.resolve({
+          tools: [
+            {
+              name: "weather",
+              description: "Get the current weather",
+              inputSchema: {
+                type: "object",
+              },
+            },
+          ],
+        })
+      );
+
+      mockClient.callTool.mockImplementation((params) => {
+        return Promise.resolve({
+          content: [
+            {
+              type: "text",
+              text: `It is currently 70 degrees and cloudy.`,
+            },
+          ],
+        });
+      });
+
+      // Load tools
+      const tools = await loadMcpTools(
+        "mockServer(should load tool with no input parameters)",
+        mockClient as Client
+      );
+
+      // Verify results
+      expect(tools.length).toBe(1);
+      expect(tools[0].name).toBe("weather");
+
+      const weatherTool = tools[0];
+
+      // should invoke the tool when input is valid
+      await expect(weatherTool.invoke({})).resolves.toEqual(
+        "It is currently 70 degrees and cloudy."
+      );
+
+      expect(mockClient.callTool).toHaveBeenCalledWith({
+        arguments: undefined,
+        name: "weather",
+      });
+    });
+
     test("should handle empty tool list", async () => {
       // Set up mock response
       mockClient.listTools.mockReturnValueOnce(

libs/langchain-mcp-adapters/src/tools.ts

@@ -8,6 +8,7 @@ import type {
   Tool as MCPTool,
 } from "@modelcontextprotocol/sdk/types.js";
 import {
+  DynamicTool,
   DynamicStructuredTool,
   type DynamicStructuredToolInput,
   type StructuredToolInterface,
@@ -264,18 +265,30 @@ export async function loadMcpTools(
         .filter((tool: MCPTool) => !!tool.name)
         .map(async (tool: MCPTool) => {
           try {
-            const dst = new DynamicStructuredTool({
-              name: `${toolNamePrefix}${tool.name}`,
-              description: tool.description || "",
-              schema: tool.inputSchema,
-              responseFormat: "content_and_artifact",
-              func: _callTool.bind(
-                null,
-                serverName,
-                tool.name,
-                client
-              ) as DynamicStructuredToolInput["func"],
-            });
+            const dst = tool.inputSchema?.properties
+              ? new DynamicStructuredTool({
+                  name: `${toolNamePrefix}${tool.name}`,
+                  description: tool.description || "",
+                  schema: tool.inputSchema,
+                  responseFormat: "content_and_artifact",
+                  func: _callTool.bind(
+                    null,
+                    serverName,
+                    tool.name,
+                    client
+                  ) as DynamicStructuredToolInput["func"],
+                })
+              : new DynamicTool({
+                  name: `${toolNamePrefix}${tool.name}`,
+                  description: tool.description || "",
+                  responseFormat: "content_and_artifact",
+                  func: _callTool.bind(
+                    null,
+                    serverName,
+                    tool.name,
+                    client
+                  ) as DynamicStructuredToolInput["func"],
+                });
             getDebugLog()(`INFO: Successfully loaded tool: ${dst.name}`);
             return dst;
           } catch (error) {