diff --git a/client/src/components/ToolResults.tsx b/client/src/components/ToolResults.tsx
index d036298b9..106312852 100644
--- a/client/src/components/ToolResults.tsx
+++ b/client/src/components/ToolResults.tsx
@@ -13,8 +13,29 @@ interface ToolResultsProps {
   resourceContent: Record<string, string>;
   onReadResource?: (uri: string) => void;
   isPollingTask?: boolean;
+  toolRunDurationMs?: number | null;
 }
 
+const formatToolRunDuration = (durationMs: number): string => {
+  const roundedMs = Math.max(0, Math.round(durationMs));
+  if (roundedMs < 1000) {
+    return `${roundedMs}ms`;
+  }
+  return `${(roundedMs / 1000).toFixed(2)}s`;
+};
+
+const ToolRunDuration = ({ durationMs }: { durationMs?: number | null }) => {
+  if (typeof durationMs !== "number" || !Number.isFinite(durationMs)) {
+    return null;
+  }
+
+  return (
+    <span className="ml-2 text-xs font-medium text-muted-foreground">
+      Took {formatToolRunDuration(durationMs)}
+    </span>
+  );
+};
+
 const checkContentCompatibility = (
   structuredContent: unknown,
   unstructuredContent: Array<{
@@ -65,6 +86,7 @@ const ToolResults = ({
   resourceContent,
   onReadResource,
   isPollingTask,
+  toolRunDurationMs,
 }: ToolResultsProps) => {
   if (!toolResult) return null;
 
@@ -73,7 +95,10 @@ const ToolResults = ({
     if (!parsedResult.success) {
       return (
         <>
-          <h4 className="font-semibold mb-2">Invalid Tool Result:</h4>
+          <h4 className="font-semibold mb-2">
+            Invalid Tool Result:
+            <ToolRunDuration durationMs={toolRunDurationMs} />
+          </h4>
           <JsonView data={toolResult} />
           <h4 className="font-semibold mb-2">Errors:</h4>
           {parsedResult.error.issues.map((issue, idx) => (
@@ -141,6 +166,7 @@ const ToolResults = ({
           ) : (
             <span className="text-green-600 font-semibold">Success</span>
           )}
+          <ToolRunDuration durationMs={toolRunDurationMs} />
         </h4>
         {structuredResult.structuredContent && (
           <div className="mb-4">
@@ -240,7 +266,10 @@ const ToolResults = ({
   } else if ("toolResult" in toolResult) {
     return (
       <>
-        <h4 className="font-semibold mb-2">Tool Result (Legacy):</h4>
+        <h4 className="font-semibold mb-2">
+          Tool Result (Legacy):
+          <ToolRunDuration durationMs={toolRunDurationMs} />
+        </h4>
         <JsonView data={toolResult.toolResult} />
       </>
     );
diff --git a/client/src/components/ToolsTab.tsx b/client/src/components/ToolsTab.tsx
index febea1d8f..02327cd1e 100644
--- a/client/src/components/ToolsTab.tsx
+++ b/client/src/components/ToolsTab.tsx
@@ -201,6 +201,9 @@ const ToolsTab = ({
   const [params, setParams] = useState<Record<string, unknown>>({});
   const [runAsTask, setRunAsTask] = useState(false);
   const [isToolRunning, setIsToolRunning] = useState(false);
+  const [toolRunDurationMs, setToolRunDurationMs] = useState<number | null>(
+    null,
+  );
   const [isOutputSchemaExpanded, setIsOutputSchemaExpanded] = useState(false);
   const [isMetadataExpanded, setIsMetadataExpanded] = useState(false);
   const [metadataEntries, setMetadataEntries] = useState<
@@ -248,6 +251,7 @@ const ToolsTab = ({
 
     // Reset validation errors when switching tools
     setHasValidationErrors(false);
+    setToolRunDurationMs(null);
 
     // Clear form refs for the previous tool
     formRefs.current = {};
@@ -808,8 +812,10 @@ const ToolsTab = ({
                     // Validate JSON inputs before calling tool
                     if (checkValidationErrors(true)) return;
 
+                    const runStartedAt = Date.now();
                     try {
                       setIsToolRunning(true);
+                      setToolRunDurationMs(null);
                       const metadata = metadataEntries.reduce<
                         Record<string, unknown>
                       >((acc, { key, value }) => {
@@ -831,6 +837,7 @@ const ToolsTab = ({
                         runAsTask,
                       );
                     } finally {
+                      setToolRunDurationMs(Date.now() - runStartedAt);
                       setIsToolRunning(false);
                     }
                   }}
@@ -886,6 +893,7 @@ const ToolsTab = ({
                   resourceContent={resourceContent}
                   onReadResource={onReadResource}
                   isPollingTask={isPollingTask}
+                  toolRunDurationMs={toolRunDurationMs}
                 />
               </div>
             ) : (
diff --git a/client/src/components/__tests__/ToolsTab.test.tsx b/client/src/components/__tests__/ToolsTab.test.tsx
index 5678914d6..fc6d66c49 100644
--- a/client/src/components/__tests__/ToolsTab.test.tsx
+++ b/client/src/components/__tests__/ToolsTab.test.tsx
@@ -423,6 +423,36 @@ describe("ToolsTab", () => {
     expect(submitButton.getAttribute("disabled")).toBeNull();
   });
 
+  it("should show how long the last tool run took", async () => {
+    let currentTime = 1000;
+    const nowSpy = jest
+      .spyOn(Date, "now")
+      .mockImplementation(() => currentTime);
+    const mockCallTool = jest.fn(async () => {
+      currentTime = 6240;
+      return { content: [] };
+    });
+
+    try {
+      renderToolsTab({
+        selectedTool: mockTools[0],
+        callTool: mockCallTool,
+        toolResult: { content: [] },
+      });
+
+      expect(screen.queryByText(/Took /)).not.toBeInTheDocument();
+
+      const submitButton = screen.getByRole("button", { name: /run tool/i });
+      await act(async () => {
+        fireEvent.click(submitButton);
+      });
+
+      expect(screen.getByText("Took 5.24s")).toBeInTheDocument();
+    } finally {
+      nowSpy.mockRestore();
+    }
+  });
+
   describe("Output Schema Display", () => {
     const toolWithOutputSchema: Tool = {
       name: "weatherTool",