diff --git a/client/src/components/ToolResults.tsx b/client/src/components/ToolResults.tsx
index d036298b9..bf8944d8b 100644
--- a/client/src/components/ToolResults.tsx
+++ b/client/src/components/ToolResults.tsx
@@ -13,8 +13,37 @@ interface ToolResultsProps {
   resourceContent: Record<string, string>;
   onReadResource?: (uri: string) => void;
   isPollingTask?: boolean;
+  /**
+   * Wall-clock time the last `callTool` invocation took, in milliseconds.
+   * `undefined` means no measurement is available (e.g. legacy result path).
+   */
+  durationMs?: number | null;
 }
 
+// Format a millisecond duration for display in the tool result header.
+// - < 1ms  -> "<1 ms"
+// - < 1s   -> "123 ms"
+// - < 1min -> "1.23 s"
+// - >= 1m  -> "1m 23.4s"
+const formatCallDuration = (durationMs: number): string => {
+  if (!Number.isFinite(durationMs) || durationMs < 0) {
+    return "";
+  }
+  if (durationMs < 1) {
+    return "<1 ms";
+  }
+  if (durationMs < 1000) {
+    return `${Math.round(durationMs)} ms`;
+  }
+  if (durationMs < 60_000) {
+    return `${(durationMs / 1000).toFixed(2)} s`;
+  }
+  const totalSeconds = Math.floor(durationMs / 1000);
+  const minutes = Math.floor(totalSeconds / 60);
+  const seconds = (durationMs - minutes * 60_000) / 1000;
+  return `${minutes}m ${seconds.toFixed(1)}s`;
+};
+
 const checkContentCompatibility = (
   structuredContent: unknown,
   unstructuredContent: Array<{
@@ -65,6 +94,7 @@ const ToolResults = ({
   resourceContent,
   onReadResource,
   isPollingTask,
+  durationMs,
 }: ToolResultsProps) => {
   if (!toolResult) return null;
 
@@ -141,6 +171,15 @@ const ToolResults = ({
           ) : (
             <span className="text-green-600 font-semibold">Success</span>
           )}
+          {typeof durationMs === "number" && (
+            <span
+              className="ml-2 text-xs font-normal text-gray-500 dark:text-gray-400"
+              data-testid="tool-call-duration"
+              title="Time taken to run the tool (round-trip)"
+            >
+              ({formatCallDuration(durationMs)})
+            </span>
+          )}
         </h4>
         {structuredResult.structuredContent && (
           <div className="mb-4">
diff --git a/client/src/components/ToolsTab.tsx b/client/src/components/ToolsTab.tsx
index febea1d8f..42656c56d 100644
--- a/client/src/components/ToolsTab.tsx
+++ b/client/src/components/ToolsTab.tsx
@@ -207,6 +207,9 @@ const ToolsTab = ({
     { id: string; key: string; value: string }[]
   >([]);
   const [hasValidationErrors, setHasValidationErrors] = useState(false);
+  const [lastCallDurationMs, setLastCallDurationMs] = useState<number | null>(
+    null,
+  );
   const formRefs = useRef<Record<string, DynamicJsonFormRef | null>>({});
   const { toast } = useToast();
   const { copied, setCopied } = useCopy();
@@ -249,6 +252,10 @@ const ToolsTab = ({
     // Reset validation errors when switching tools
     setHasValidationErrors(false);
 
+    // Reset the recorded duration so the previous tool's timing doesn't
+    // appear next to the new tool's result.
+    setLastCallDurationMs(null);
+
     // Clear form refs for the previous tool
     formRefs.current = {};
   }, [selectedTool, serverSupportsTaskRequests]);
@@ -824,12 +831,19 @@ const ToolsTab = ({
                         }
                         return acc;
                       }, {});
-                      await callTool(
-                        selectedTool.name,
-                        params,
-                        Object.keys(metadata).length ? metadata : undefined,
-                        runAsTask,
-                      );
+                      // Measure the call duration so the user can see how
+                      // long the tool took to respond (issue #1284).
+                      const startTime = performance.now();
+                      try {
+                        await callTool(
+                          selectedTool.name,
+                          params,
+                          Object.keys(metadata).length ? metadata : undefined,
+                          runAsTask,
+                        );
+                      } finally {
+                        setLastCallDurationMs(performance.now() - startTime);
+                      }
                     } finally {
                       setIsToolRunning(false);
                     }
@@ -886,6 +900,7 @@ const ToolsTab = ({
                   resourceContent={resourceContent}
                   onReadResource={onReadResource}
                   isPollingTask={isPollingTask}
+                  durationMs={lastCallDurationMs}
                 />
               </div>
             ) : (
diff --git a/client/src/components/__tests__/ToolsTab.test.tsx b/client/src/components/__tests__/ToolsTab.test.tsx
index 5678914d6..ca041aa0f 100644
--- a/client/src/components/__tests__/ToolsTab.test.tsx
+++ b/client/src/components/__tests__/ToolsTab.test.tsx
@@ -2,7 +2,10 @@ import { render, screen, fireEvent, act } from "@testing-library/react";
 import "@testing-library/jest-dom";
 import { describe, it, jest, beforeEach } from "@jest/globals";
 import ToolsTab, { ExtendedTool } from "../ToolsTab";
-import { Tool } from "@modelcontextprotocol/sdk/types.js";
+import {
+  CompatibilityCallToolResult,
+  Tool,
+} from "@modelcontextprotocol/sdk/types.js";
 import { Tabs } from "../ui/tabs";
 import { cacheToolOutputSchemas } from "../../utils/schemaUtils";
 import { within } from "@testing-library/react";
@@ -1203,4 +1206,81 @@ describe("ToolsTab", () => {
       expect(mockCallTool).toHaveBeenCalled();
     });
   });
+
+  describe("Tool call duration display", () => {
+    const successfulResult: CompatibilityCallToolResult = {
+      content: [{ type: "text", text: "ok" }],
+    };
+
+    it("should show the call duration next to the result after running a tool", async () => {
+      // Add a small but measurable delay so durationMs > 0 in jsdom.
+      const callToolMock = jest.fn(
+        () =>
+          new Promise<CompatibilityCallToolResult>((resolve) =>
+            setTimeout(() => resolve(successfulResult), 25),
+          ),
+      );
+
+      renderToolsTab({
+        selectedTool: mockTools[0],
+        callTool: callToolMock,
+        toolResult: null,
+      });
+
+      const runButton = screen.getByRole("button", { name: /run tool/i });
+      await act(async () => {
+        fireEvent.click(runButton);
+      });
+
+      // Re-render with the now-available result so the duration surfaces.
+      renderToolsTab({
+        selectedTool: mockTools[0],
+        callTool: callToolMock,
+        toolResult: successfulResult,
+      });
+
+      const durationEl = await screen.findByTestId("tool-call-duration");
+      expect(durationEl).toBeInTheDocument();
+      // The formatted duration is one of "<1 ms", "N ms", "N.NN s", or "Nm N.Ns".
+      expect(durationEl.textContent).toMatch(/ms|s|m\s/);
+    });
+
+    it("should not show the call duration when none has been recorded", () => {
+      renderToolsTab({
+        selectedTool: mockTools[0],
+        toolResult: successfulResult,
+      });
+
+      expect(screen.queryByTestId("tool-call-duration")).not.toBeInTheDocument();
+    });
+
+    it("should clear the recorded duration when switching tools", async () => {
+      const callToolMock = jest.fn(async () => successfulResult);
+
+      const { rerender } = renderToolsTab({
+        selectedTool: mockTools[0],
+        callTool: callToolMock,
+        toolResult: null,
+      });
+
+      const runButton = screen.getByRole("button", { name: /run tool/i });
+      await act(async () => {
+        fireEvent.click(runButton);
+      });
+
+      // Switch to another tool - duration should be reset.
+      rerender(
+        <Tabs defaultValue="tools">
+          <ToolsTab
+            {...defaultProps}
+            selectedTool={mockTools[2]}
+            callTool={callToolMock}
+            toolResult={null}
+          />
+        </Tabs>,
+      );
+
+      expect(screen.queryByTestId("tool-call-duration")).not.toBeInTheDocument();
+    });
+  });
 });