diff --git a/frontend/src/api/services.ts b/frontend/src/api/services.ts
index edcc0fa..0a19327 100644
--- a/frontend/src/api/services.ts
+++ b/frontend/src/api/services.ts
@@ -2,6 +2,7 @@ import { del, get, post, put } from "./shared";
 import type {
 	ServiceInstance,
 	ServiceInstanceInput,
+	ServiceTestResult,
 	ServiceTypeInfo,
 } from "../types";
 
@@ -36,3 +37,9 @@ export async function deleteServiceInstance(
 ): Promise<{ status: string }> {
 	return del<{ status: string }>(`/api/services/instances/${serviceId}`);
 }
+
+export async function testServiceInstance(
+	input: ServiceInstanceInput,
+): Promise<ServiceTestResult> {
+	return post<ServiceTestResult>("/api/services/test", input);
+}
diff --git a/frontend/src/components/ServiceTestPanel.tsx b/frontend/src/components/ServiceTestPanel.tsx
new file mode 100644
index 0000000..167f2ce
--- /dev/null
+++ b/frontend/src/components/ServiceTestPanel.tsx
@@ -0,0 +1,72 @@
+import { Alert, AlertDescription } from "@/components/ui/alert";
+import { Button } from "@/components/ui/button";
+import type { ServiceTestResult } from "../types";
+
+interface Props {
+	/** Current test result (null = not tested yet). Parent clears this when the form input changes. */
+	result: ServiceTestResult | null;
+	/** Whether the test mutation is in-flight. */
+	isPending: boolean;
+	/** Whether the "Save anyway" checkbox is checked. */
+	saveAnyway: boolean;
+	/** Fired when the user clicks "Test credentials". */
+	onTest: () => void;
+	/** Fired when the "Save anyway" checkbox toggles. */
+	onSaveAnywayChange: (checked: boolean) => void;
+	/** Disable the Test button (e.g. no draft yet). */
+	disabled?: boolean;
+}
+
+/**
+ * Shared "Test credentials" panel used by both the add-service dialog and the
+ * edit-service panel. Purely presentational — the parent owns the test result
+ * + saveAnyway state and the mutation hook. This avoids setState-in-effect
+ * issues with clearing the result on input change (the parent uses the
+ * React-recommended "store previous prop" pattern instead).
+ */
+export function ServiceTestPanel({
+	result,
+	isPending,
+	saveAnyway,
+	onTest,
+	onSaveAnywayChange,
+	disabled,
+}: Props) {
+	const testPassed = result?.ok === true;
+
+	return (
+		<div className="flex flex-col gap-2">
+			<Button
+				variant="outline"
+				size="sm"
+				onClick={onTest}
+				disabled={isPending || disabled}
+				className="mobile-touch-target"
+			>
+				{isPending ? "Testing…" : "Test credentials"}
+			</Button>
+			{result ? (
+				<Alert variant={result.ok ? "default" : "destructive"}>
+					<AlertDescription>
+						{result.ok
+							? `✓ Connected${result.evidence ? ` — ${result.evidence}` : ""}`
+							: `✗ ${result.detail}`}
+					</AlertDescription>
+				</Alert>
+			) : null}
+			<label className="flex items-center gap-2 text-xs text-muted-foreground">
+				<input
+					type="checkbox"
+					checked={saveAnyway}
+					onChange={(e) => onSaveAnywayChange(e.target.checked)}
+				/>
+				Save anyway (skip test)
+			</label>
+			{!testPassed && !saveAnyway ? (
+				<p className="text-xs text-muted-foreground">
+					Test credentials or check "Save anyway" to enable the save button.
+				</p>
+			) : null}
+		</div>
+	);
+}
diff --git a/frontend/src/components/__tests__/ServiceTestPanel.test.tsx b/frontend/src/components/__tests__/ServiceTestPanel.test.tsx
new file mode 100644
index 0000000..6ffd441
--- /dev/null
+++ b/frontend/src/components/__tests__/ServiceTestPanel.test.tsx
@@ -0,0 +1,115 @@
+import { describe, it, expect, vi } from "vitest";
+import { render, screen, fireEvent } from "@testing-library/react";
+import { ServiceTestPanel } from "../ServiceTestPanel";
+import type { ServiceTestResult } from "../../types";
+
+function noop() {}
+
+describe("ServiceTestPanel", () => {
+	it("renders the Test credentials button", () => {
+		render(
+			<ServiceTestPanel
+				result={null}
+				isPending={false}
+				saveAnyway={false}
+				onTest={noop}
+				onSaveAnywayChange={noop}
+			/>,
+		);
+		expect(screen.getByText("Test credentials")).toBeTruthy();
+	});
+
+	it("shows Testing… and disables button while pending", () => {
+		render(
+			<ServiceTestPanel
+				result={null}
+				isPending={true}
+				saveAnyway={false}
+				onTest={noop}
+				onSaveAnywayChange={noop}
+			/>,
+		);
+		expect(screen.getByText("Testing…")).toBeTruthy();
+		expect(screen.getByText("Testing…")).toBeDisabled();
+	});
+
+	it("renders green ✓ Connected pill with evidence on success", () => {
+		const result: ServiceTestResult = {
+			ok: true,
+			detail: "ok",
+			evidence: "v4.5.0",
+		};
+		render(
+			<ServiceTestPanel
+				result={result}
+				isPending={false}
+				saveAnyway={false}
+				onTest={noop}
+				onSaveAnywayChange={noop}
+			/>,
+		);
+		expect(screen.getByText(/✓ Connected — v4.5.0/)).toBeTruthy();
+	});
+
+	it("renders red ✗ pill with detail on failure", () => {
+		const result: ServiceTestResult = {
+			ok: false,
+			detail: "Authentication failed",
+			evidence: null,
+		};
+		render(
+			<ServiceTestPanel
+				result={result}
+				isPending={false}
+				saveAnyway={false}
+				onTest={noop}
+				onSaveAnywayChange={noop}
+			/>,
+		);
+		expect(screen.getByText(/✗ Authentication failed/)).toBeTruthy();
+	});
+
+	it("fires onTest when Test credentials is clicked", () => {
+		const onTest = vi.fn();
+		render(
+			<ServiceTestPanel
+				result={null}
+				isPending={false}
+				saveAnyway={false}
+				onTest={onTest}
+				onSaveAnywayChange={noop}
+			/>,
+		);
+		fireEvent.click(screen.getByText("Test credentials"));
+		expect(onTest).toHaveBeenCalledOnce();
+	});
+
+	it("fires onSaveAnywayChange when checkbox is toggled", () => {
+		const onSaveAnywayChange = vi.fn();
+		render(
+			<ServiceTestPanel
+				result={null}
+				isPending={false}
+				saveAnyway={false}
+				onTest={noop}
+				onSaveAnywayChange={onSaveAnywayChange}
+			/>,
+		);
+		const checkbox = screen.getByRole("checkbox");
+		fireEvent.click(checkbox);
+		expect(onSaveAnywayChange).toHaveBeenCalledWith(true);
+	});
+
+	it("renders the Save anyway checkbox", () => {
+		render(
+			<ServiceTestPanel
+				result={null}
+				isPending={false}
+				saveAnyway={false}
+				onTest={noop}
+				onSaveAnywayChange={noop}
+			/>,
+		);
+		expect(screen.getByRole("checkbox")).toBeTruthy();
+	});
+});
diff --git a/frontend/src/hooks/useServices.ts b/frontend/src/hooks/useServices.ts
index a83848e..b4456a4 100644
--- a/frontend/src/hooks/useServices.ts
+++ b/frontend/src/hooks/useServices.ts
@@ -4,6 +4,7 @@ import {
 	deleteServiceInstance,
 	fetchServiceInstances,
 	fetchServiceTypes,
+	testServiceInstance,
 	updateServiceInstance,
 } from "../api/services";
 import type { ServiceInstanceInput } from "../types";
@@ -45,3 +46,9 @@ export function useDeleteServiceInstance() {
 		},
 	});
 }
+
+export function useTestServiceInstance() {
+	return useMutation({
+		mutationFn: (input: ServiceInstanceInput) => testServiceInstance(input),
+	});
+}
diff --git a/frontend/src/pages/ServicesPage.tsx b/frontend/src/pages/ServicesPage.tsx
index 7d4d64b..7f4faed 100644
--- a/frontend/src/pages/ServicesPage.tsx
+++ b/frontend/src/pages/ServicesPage.tsx
@@ -30,6 +30,7 @@ import {
 	useDeleteServiceInstance,
 	useSaveServiceInstance,
 	useServiceInstances,
+	useTestServiceInstance,
 } from "../hooks/useServices";
 import { useServiceTypes } from "../hooks/useServices";
 import {
@@ -41,12 +42,14 @@ import type {
 	SecretFieldInfo,
 	ServiceInstance,
 	ServiceInstanceInput,
+	ServiceTestResult,
 	ServiceTypeInfo,
 } from "../types";
 import { SectionCard } from "../components/SectionCard";
 import { ConfirmDialog } from "../components/ConfirmDialog";
 import { DialogFooter } from "../components/DialogFooter";
 import { getServiceBinding } from "../integrations/registry";
+import { ServiceTestPanel } from "../components/ServiceTestPanel";
 import { serviceLinkTarget } from "../components/PinnedServiceLink";
 import type { NamedDashboardInput } from "../api/dashboards";
 
@@ -174,12 +177,48 @@ function CreateServiceDialog({
 }) {
 	const { data: types = [] } = useServiceTypes();
 	const saveService = useSaveServiceInstance();
+	const testService = useTestServiceInstance();
 	const [draft, setDraft] = useState<CreateDraft | null>(null);
 	const [submitError, setSubmitError] = useState<string | null>(null);
+	const [testResult, setTestResult] = useState<ServiceTestResult | null>(null);
+	const [saveAnyway, setSaveAnyway] = useState(false);
+
+	// Reset test state when draft changes (React "store previous" pattern —
+	// avoids setState-in-effect). Any field edit creates a new draft object.
+	const [prevDraft, setPrevDraft] = useState(draft);
+	if (draft !== prevDraft) {
+		setPrevDraft(draft);
+		setTestResult(null);
+		setSaveAnyway(false);
+	}
+
+	const testPassed = (testResult?.ok ?? false) || saveAnyway;
 
 	function reset() {
 		setDraft(null);
 		setSubmitError(null);
+		setTestResult(null);
+		setSaveAnyway(false);
+	}
+
+	async function handleTest() {
+		if (!draft) return;
+		try {
+			const res = await testService.mutateAsync({
+				service_type: draft.serviceType,
+				name: draft.name.trim(),
+				config: draft.config,
+				secrets: draft.secrets,
+				enabled: draft.enabled,
+			});
+			setTestResult(res);
+		} catch (err) {
+			setTestResult({
+				ok: false,
+				detail: err instanceof Error ? err.message : String(err),
+				evidence: null,
+			});
+		}
 	}
 
 	async function save() {
@@ -196,7 +235,7 @@ function CreateServiceDialog({
 		try {
 			await saveService.mutateAsync(input);
 			reset();
-		onClose();
+			onClose();
 		} catch (err) {
 			setSubmitError(err instanceof Error ? err.message : String(err));
 		}
@@ -265,9 +304,16 @@ function CreateServiceDialog({
 									onCheckedChange={(checked) =>
 										setDraft({ ...draft, enabled: checked })
 									}
-								/>
-								<Label htmlFor="service-enabled">Enabled</Label>
-							</div>
+							/>
+							<Label htmlFor="service-enabled">Enabled</Label>
+						</div>
+						<ServiceTestPanel
+							result={testResult}
+							isPending={testService.isPending}
+							saveAnyway={saveAnyway}
+							onTest={handleTest}
+							onSaveAnywayChange={setSaveAnyway}
+						/>
 						</>
 					)}
 				</div>
@@ -281,7 +327,7 @@ function CreateServiceDialog({
 						onCancel={reset}
 						onConfirm={save}
 						confirmLabel="Create service"
-						confirmDisabled={!draft.name.trim() || saveService.isPending}
+						confirmDisabled={!draft.name.trim() || saveService.isPending || !testPassed}
 					/>
 				) : null}
 			</DialogContent>
diff --git a/frontend/src/pages/Settings.tsx b/frontend/src/pages/Settings.tsx
index 4eb6d78..ef86231 100644
--- a/frontend/src/pages/Settings.tsx
+++ b/frontend/src/pages/Settings.tsx
@@ -55,10 +55,13 @@ import {
 	useSaveServiceInstance,
 	useServiceInstances,
 	useServiceTypes,
+	useTestServiceInstance,
 } from "../hooks/useServices";
+import { ServiceTestPanel } from "../components/ServiceTestPanel";
 import type {
 	ServiceInstance,
 	ServiceInstanceInput,
+	ServiceTestResult,
 	ServiceTypeInfo,
 } from "../types";
 
@@ -1435,6 +1438,7 @@ function ServiceConfigEditor({
 }) {
 	const saveService = useSaveServiceInstance();
 	const deleteService = useDeleteServiceInstance();
+	const testService = useTestServiceInstance();
 	const [name, setName] = useState(instance.name);
 	const [enabled, setEnabled] = useState(instance.enabled);
 	const [draftConfig, setDraftConfig] = useState<Record<string, unknown>>({
@@ -1442,6 +1446,49 @@ function ServiceConfigEditor({
 	});
 	const [draftSecrets, setDraftSecrets] = useState<Record<string, string>>({});
 	const [deleteOpen, setDeleteOpen] = useState(false);
+	const [testResult, setTestResult] = useState<ServiceTestResult | null>(null);
+	const [saveAnyway, setSaveAnyway] = useState(false);
+
+	// Build a test input from the current editor state. For the test, include
+	// ALL typed secrets (unfiltered) so the backend can authenticate.
+	function buildTestInput(): ServiceInstanceInput {
+		return {
+			id: instance.id,
+			service_type: instance.service_type,
+			name,
+			config: draftConfig,
+			secrets: draftSecrets,
+			enabled,
+		};
+	}
+
+	const testInput = buildTestInput();
+
+	// Reset test state when the test input changes (store-previous pattern).
+	const [prevTestInput, setPrevTestInput] = useState(testInput);
+	if (
+		testInput !== prevTestInput &&
+		JSON.stringify(testInput) !== JSON.stringify(prevTestInput)
+	) {
+		setPrevTestInput(testInput);
+		setTestResult(null);
+		setSaveAnyway(false);
+	}
+
+	const testPassed = (testResult?.ok ?? false) || saveAnyway;
+
+	async function handleTest() {
+		try {
+			const res = await testService.mutateAsync(testInput);
+			setTestResult(res);
+		} catch (err) {
+			setTestResult({
+				ok: false,
+				detail: err instanceof Error ? err.message : String(err),
+				evidence: null,
+			});
+		}
+	}
 
 	const properties =
 		(
@@ -1560,10 +1607,18 @@ function ServiceConfigEditor({
 								</FormField>
 							))}
 
+					<ServiceTestPanel
+						result={testResult}
+						isPending={testService.isPending}
+						saveAnyway={saveAnyway}
+						onTest={handleTest}
+						onSaveAnywayChange={setSaveAnyway}
+					/>
+
 					<div className="flex justify-between">
 						<Button
 							onClick={handleSave}
-							disabled={saveService.isPending}
+							disabled={saveService.isPending || !testPassed}
 							className="mobile-touch-target"
 						>
 							Save
diff --git a/frontend/src/types/index.ts b/frontend/src/types/index.ts
index 43f5cb7..e5ac9c1 100644
--- a/frontend/src/types/index.ts
+++ b/frontend/src/types/index.ts
@@ -473,6 +473,12 @@ export interface ServiceInstanceInput {
 	enabled: boolean;
 }
 
+export interface ServiceTestResult {
+	ok: boolean;
+	detail: string;
+	evidence: string | null;
+}
+
 export interface BuiltinWidgetKindInfo {
 	kind: string;
 	name: string;