diff --git a/app/server/app.ts b/app/server/app.ts
index fca8126f..bdf541fe 100644
--- a/app/server/app.ts
+++ b/app/server/app.ts
@@ -92,9 +92,9 @@ export const createApp = () => {
 			logger.error(err.cause.message);
 		}
 
-		const { status, message } = handleServiceError(err);
+		const { status, message, details } = handleServiceError(err);
 
-		return c.json({ message }, status as 500);
+		return c.json(details ? { message, details } : { message }, status as 500);
 	});
 
 	return app;
diff --git a/app/server/modules/backups/__tests__/backups.execution.test.ts b/app/server/modules/backups/__tests__/backups.execution.test.ts
index bc984c58..6d273d7e 100644
--- a/app/server/modules/backups/__tests__/backups.execution.test.ts
+++ b/app/server/modules/backups/__tests__/backups.execution.test.ts
@@ -177,6 +177,36 @@ describe("stop backup", () => {
 		expect(updatedSchedule.lastBackupError).toBe("error: open /mnt/data/private.db: permission denied");
 	});
 
+	test("should store restic diagnostic details instead of the generic summary on hard failure", async () => {
+		const { resticBackupMock } = setup();
+		const volume = await createTestVolume();
+		const repository = await createTestRepository();
+		const schedule = await createTestBackupSchedule({
+			volumeId: volume.id,
+			repositoryId: repository.id,
+		});
+
+		resticBackupMock.mockImplementationOnce((params: SafeSpawnParams) => {
+			params.onStderr?.("Permissions 0755 for '/tmp/zerobyte-ssh-key' are too open.");
+			params.onStderr?.("This private key will be ignored.");
+
+			return Promise.resolve({
+				exitCode: 1,
+				summary: "",
+				error: "ssh command exited",
+				stderr: "Permissions 0755 for '/tmp/zerobyte-ssh-key' are too open.\nThis private key will be ignored.",
+			});
+		});
+
+		await backupsExecutionService.executeBackup(schedule.id);
+
+		const updatedSchedule = await backupsService.getScheduleById(schedule.id);
+		expect(updatedSchedule.lastBackupStatus).toBe("error");
+		expect(updatedSchedule.lastBackupError).toBe(
+			"Permissions 0755 for '/tmp/zerobyte-ssh-key' are too open.\nThis private key will be ignored.",
+		);
+	});
+
 	test("should stop a running backup", async () => {
 		// arrange
 		const { resticBackupMock } = setup();
diff --git a/app/server/modules/backups/backups.execution.ts b/app/server/modules/backups/backups.execution.ts
index 11a8ba4e..d6c68518 100644
--- a/app/server/modules/backups/backups.execution.ts
+++ b/app/server/modules/backups/backups.execution.ts
@@ -4,7 +4,7 @@ import { restic } from "../../core/restic";
 import { logger } from "@zerobyte/core/node";
 import { cache, cacheKeys } from "../../utils/cache";
 import { getVolumePath } from "../volumes/helpers";
-import { toMessage } from "../../utils/errors";
+import { toErrorDetails, toMessage } from "../../utils/errors";
 import { serverEvents } from "../../core/events";
 import { notificationsService } from "../notifications/notifications.service";
 import { repoMutex } from "../../core/repository-mutex";
@@ -225,11 +225,12 @@ const handleBackupFailure = async (
 	partialContext?: Partial<BackupContext>,
 ): Promise<void> => {
 	const errorMessage = toMessage(error);
+	const errorDetails = toErrorDetails(error);
 
 	await scheduleQueries.updateStatus(scheduleId, organizationId, {
 		lastBackupAt: Date.now(),
 		lastBackupStatus: "error",
-		lastBackupError: errorMessage,
+		lastBackupError: errorDetails,
 	});
 
 	if (partialContext?.schedule && partialContext?.volume && partialContext?.repository) {
@@ -252,7 +253,7 @@ const handleBackupFailure = async (
 				volumeName: ctx.volume.name,
 				repositoryName: ctx.repository.name,
 				scheduleName: ctx.schedule.name,
-				error: errorMessage,
+				error: errorDetails,
 			})
 			.catch((notifError) => {
 				logger.error(`Failed to send backup failure notification: ${toMessage(notifError)}`);
diff --git a/app/server/modules/repositories/__tests__/repositories.controller.test.ts b/app/server/modules/repositories/__tests__/repositories.controller.test.ts
index ed8d0b75..7b255ec3 100644
--- a/app/server/modules/repositories/__tests__/repositories.controller.test.ts
+++ b/app/server/modules/repositories/__tests__/repositories.controller.test.ts
@@ -341,7 +341,8 @@ describe("repositories updates", () => {
 
 				expect(res.status).toBe(500);
 				const body = await res.json();
-				expect(body.message).toContain("Command failed");
+				expect(body.message).toBe("Command failed: An error occurred while executing the command.");
+				expect(body.details).toBe("Fatal: unexpected HTTP response (403): 403 Forbidden");
 			} finally {
 				deleteSnapshotSpy.mockRestore();
 			}
diff --git a/app/server/utils/__tests__/spawn.test.ts b/app/server/utils/__tests__/spawn.test.ts
index 7758eea8..66164c42 100644
--- a/app/server/utils/__tests__/spawn.test.ts
+++ b/app/server/utils/__tests__/spawn.test.ts
@@ -206,6 +206,15 @@ describe("safeSpawn", () => {
 			expect(result.error).toBe("err_last");
 		});
 
+		test("stderr keeps the full stderr output", async () => {
+			const result = await safeSpawn({
+				command: "sh",
+				args: ["-c", "echo err_first >&2 && echo err_last >&2 && exit 1"],
+			});
+
+			expect(result.stderr).toBe("err_first\nerr_last");
+		});
+
 		test("returns exitCode -1 when the command is not found", async () => {
 			const result = await safeSpawn({
 				command: "this-command-does-not-exist-zerobyte",
diff --git a/app/server/utils/errors.ts b/app/server/utils/errors.ts
index b592505e..d1adf687 100644
--- a/app/server/utils/errors.ts
+++ b/app/server/utils/errors.ts
@@ -1,11 +1,20 @@
 import { HttpError } from "http-errors-enhanced";
 import { sanitizeSensitiveData } from "@zerobyte/core/node";
+import { ResticError } from "@zerobyte/core/restic";
 
 export const handleServiceError = (error: unknown) => {
 	if (error instanceof HttpError) {
 		return { message: sanitizeSensitiveData(error.message), status: error.statusCode };
 	}
 
+	if (error instanceof ResticError) {
+		return {
+			message: sanitizeSensitiveData(error.summary),
+			details: error.details ? sanitizeSensitiveData(error.details) : undefined,
+			status: 500 as const,
+		};
+	}
+
 	return { message: sanitizeSensitiveData(toMessage(error)), status: 500 as const };
 };
 
@@ -13,3 +22,11 @@ export const toMessage = (err: unknown): string => {
 	const message = err instanceof Error ? err.message : String(err);
 	return sanitizeSensitiveData(message);
 };
+
+export const toErrorDetails = (err: unknown): string => {
+	if (err instanceof ResticError) {
+		return sanitizeSensitiveData(err.details || err.summary);
+	}
+
+	return toMessage(err);
+};
diff --git a/packages/core/src/restic/commands/__tests__/backup.test.ts b/packages/core/src/restic/commands/__tests__/backup.test.ts
index 476c253f..9c4eb763 100644
--- a/packages/core/src/restic/commands/__tests__/backup.test.ts
+++ b/packages/core/src/restic/commands/__tests__/backup.test.ts
@@ -301,6 +301,27 @@ describe("backup command", () => {
 			expect((error as ResticError).code).toBe(12);
 		});
 
+		test("stores restic summary separately from diagnostic stderr", async () => {
+			setup({
+				spawnResult: {
+					exitCode: 1,
+					summary: "",
+					error: "ssh command exited",
+				},
+				onSpawnCall: (params) => {
+					params.onStderr?.("Permissions 0755 for '/tmp/zerobyte-ssh-key' are too open.");
+					params.onStderr?.("This private key will be ignored.");
+				},
+			});
+
+			const error = await backup(config, "/mnt/data", { organizationId: "org-1" }, mockDeps).catch((e) => e);
+			expect(error).toBeInstanceOf(ResticError);
+			expect((error as ResticError).summary).toBe("Command failed: An error occurred while executing the command.");
+			expect((error as ResticError).details).toBe(
+				"Permissions 0755 for '/tmp/zerobyte-ssh-key' are too open.\nThis private key will be ignored.",
+			);
+		});
+
 		test("returns { result: null } when the abort signal is triggered", async () => {
 			const controller = new AbortController();
 			setup({
diff --git a/packages/core/src/restic/commands/backup.ts b/packages/core/src/restic/commands/backup.ts
index 1a9078e1..ed414fcc 100644
--- a/packages/core/src/restic/commands/backup.ts
+++ b/packages/core/src/restic/commands/backup.ts
@@ -181,7 +181,7 @@ export const backup = async (
 		logger.error(`Restic backup failed: ${res.error}`);
 		logger.error(`Command executed: restic ${args.join(" ")}`);
 
-		throw new ResticError(res.exitCode, res.error);
+		throw new ResticError(res.exitCode, stderrLines.join("\n") || res.stderr || res.error);
 	}
 
 	const lastLine = res.summary.trim();
diff --git a/packages/core/src/restic/commands/ls.ts b/packages/core/src/restic/commands/ls.ts
index 1d703025..4ea52265 100644
--- a/packages/core/src/restic/commands/ls.ts
+++ b/packages/core/src/restic/commands/ls.ts
@@ -126,7 +126,7 @@ export const ls = async (
 
 	if (res.exitCode !== 0) {
 		logger.error(`Restic ls failed: ${res.error}`);
-		throw new ResticError(res.exitCode, res.error);
+		throw new ResticError(res.exitCode, res.stderr || res.error);
 	}
 
 	if (totalNodes > offset + limit) {
diff --git a/packages/core/src/restic/commands/restore.ts b/packages/core/src/restic/commands/restore.ts
index 8788f0c1..2f298e49 100644
--- a/packages/core/src/restic/commands/restore.ts
+++ b/packages/core/src/restic/commands/restore.ts
@@ -134,7 +134,7 @@ export const restore = async (
 
 	if (res.exitCode !== 0) {
 		logger.error(`Restic restore failed: ${res.error}`);
-		throw new ResticError(res.exitCode, res.error);
+		throw new ResticError(res.exitCode, res.stderr || res.error);
 	}
 
 	const lastLine = res.summary.trim();
diff --git a/packages/core/src/restic/error.ts b/packages/core/src/restic/error.ts
index 60e039b7..7f631543 100644
--- a/packages/core/src/restic/error.ts
+++ b/packages/core/src/restic/error.ts
@@ -10,12 +10,16 @@ const resticErrorCodes: Record<number, string> = {
 
 export class ResticError extends Error {
 	code: number;
+	summary: string;
+	details: string;
 
-	constructor(code: number, stderr: string) {
-		const message = resticErrorCodes[code] || `Unknown restic error with code ${code}`;
-		super(`${message}\n${stderr}`);
+	constructor(code: number, details: string) {
+		const summary = resticErrorCodes[code] || `Unknown restic error with code ${code}`;
+		super(details ? `${summary}\n${details}` : summary);
 
 		this.code = code;
+		this.summary = summary;
+		this.details = details;
 		this.name = "ResticError";
 	}
 }
diff --git a/packages/core/src/utils/spawn.ts b/packages/core/src/utils/spawn.ts
index 35b2e0e0..5d173b23 100644
--- a/packages/core/src/utils/spawn.ts
+++ b/packages/core/src/utils/spawn.ts
@@ -59,6 +59,7 @@ export type SpawnResult = {
 	exitCode: number;
 	summary: string;
 	error: string;
+	stderr?: string;
 };
 
 export function safeSpawn(params: SafeSpawnParamsLines): Promise<SpawnResult>;
@@ -70,6 +71,7 @@ export function safeSpawn(params: SafeSpawnParams): Promise<SpawnResult> {
 
 	let lastStdout = "";
 	let lastStderr = "";
+	let stderr = "";
 
 	return new Promise<SpawnResult>((resolve) => {
 		const child = spawn(command, args, {
@@ -101,6 +103,7 @@ export function safeSpawn(params: SafeSpawnParams): Promise<SpawnResult> {
 
 		rlErr.on("line", (line) => {
 			if (onStderr) onStderr(line);
+			stderr += `${line}\n`;
 			const trimmed = line.trim();
 			if (trimmed.length > 0) {
 				lastStderr = line;
@@ -115,6 +118,7 @@ export function safeSpawn(params: SafeSpawnParams): Promise<SpawnResult> {
 				exitCode: -1,
 				summary: lastStdout,
 				error: err.message || lastStderr,
+				stderr: stderr.trim(),
 			});
 		});
 
@@ -123,6 +127,7 @@ export function safeSpawn(params: SafeSpawnParams): Promise<SpawnResult> {
 				exitCode: code ?? -1,
 				summary: lastStdout,
 				error: lastStderr,
+				stderr: stderr.trim(),
 			});
 		});
 	});