diff --git a/actions/setup/js/mcp_server_core.cjs b/actions/setup/js/mcp_server_core.cjs
index 370574379c2..7b707a21c4e 100644
--- a/actions/setup/js/mcp_server_core.cjs
+++ b/actions/setup/js/mcp_server_core.cjs
@@ -772,9 +772,10 @@ async function handleRequest(server, request, defaultHandler) {
       if (missing.length) {
         const hasRequiredFields = tool.inputSchema && Array.isArray(tool.inputSchema.required) && tool.inputSchema.required.length > 0;
         if (hasRequiredFields && Object.keys(args).length === 0) {
+          const schemaGuidance = generateEnhancedErrorMessage(tool.inputSchema.required, name, tool.inputSchema);
           throw {
             code: -32602,
-            message: `Empty arguments are not allowed — this tool is write-once, not a discovery probe. To inspect the schema, use the tools/list MCP method. To signal that no action is needed, call \`noop\` with a \`message\`.`,
+            message: `Empty arguments are not allowed — this tool is write-once, not a discovery probe. To inspect the schema, use the tools/list MCP method. To signal that no action is needed, call \`noop\` with a \`message\`.\n\n${schemaGuidance}`,
           };
         }
         throw {
@@ -941,10 +942,11 @@ async function handleMessage(server, req, defaultHandler) {
       if (missing.length) {
         const hasRequiredFields = tool.inputSchema && Array.isArray(tool.inputSchema.required) && tool.inputSchema.required.length > 0;
         if (hasRequiredFields && Object.keys(args).length === 0) {
+          const schemaGuidance = generateEnhancedErrorMessage(tool.inputSchema.required, name, tool.inputSchema);
           server.replyError(
             id,
             -32602,
-            `Empty arguments are not allowed — this tool is write-once, not a discovery probe. To inspect the schema, use the tools/list MCP method. To signal that no action is needed, call \`noop\` with a \`message\`.`
+            `Empty arguments are not allowed — this tool is write-once, not a discovery probe. To inspect the schema, use the tools/list MCP method. To signal that no action is needed, call \`noop\` with a \`message\`.\n\n${schemaGuidance}`
           );
           return;
         }
diff --git a/actions/setup/js/mcp_server_core.test.cjs b/actions/setup/js/mcp_server_core.test.cjs
index 7f86c1529d4..e5819d785fc 100644
--- a/actions/setup/js/mcp_server_core.test.cjs
+++ b/actions/setup/js/mcp_server_core.test.cjs
@@ -354,6 +354,9 @@ describe("mcp_server_core.cjs", () => {
       expect(results[0].error.message).toContain("write-once, not a discovery probe");
       expect(results[0].error.message).toContain("tools/list");
       expect(results[0].error.message).toContain("noop");
+      // Schema guidance should be included so the model can retry without calling tools/list
+      expect(results[0].error.message).toContain("Example:");
+      expect(results[0].error.message).toContain("Required parameter");
     });
 
     it("should return enhanced error for partially-supplied but invalid required fields", async () => {
@@ -568,6 +571,43 @@ describe("mcp_server_core.cjs", () => {
       expect(response.error.message).toContain("too short");
       expect(response.error.message).toContain("20");
     });
+
+    it("should return error for empty arguments object (probe detection) via handleRequest", async () => {
+      const { createServer, registerTool, handleRequest } = await import("./mcp_server_core.cjs");
+      const server = createServer({ name: "test-server", version: "1.0.0" });
+
+      registerTool(server, {
+        name: "probe_tool",
+        description: "A tool to test probe detection",
+        inputSchema: {
+          type: "object",
+          properties: { input: { type: "string", description: "Some input" } },
+          required: ["input"],
+        },
+        handler: args => ({
+          content: [{ type: "text", text: `received: ${args.input}` }],
+        }),
+      });
+
+      const response = await handleRequest(server, {
+        jsonrpc: "2.0",
+        id: 10,
+        method: "tools/call",
+        params: {
+          name: "probe_tool",
+          arguments: {}, // completely empty — probe attempt
+        },
+      });
+
+      expect(response.error).toBeDefined();
+      expect(response.error.code).toBe(-32602);
+      expect(response.error.message).toContain("write-once, not a discovery probe");
+      expect(response.error.message).toContain("tools/list");
+      expect(response.error.message).toContain("noop");
+      // Schema guidance should be included so the model can retry without calling tools/list
+      expect(response.error.message).toContain("Example:");
+      expect(response.error.message).toContain("Required parameter");
+    });
   });
 
   describe("loadToolHandlers", () => {