diff --git a/back/validation/schedule.ts b/back/validation/schedule.ts
index db9d31f8..0e1df1b7 100644
--- a/back/validation/schedule.ts
+++ b/back/validation/schedule.ts
@@ -44,7 +44,7 @@ export const commonCronSchema = {
   name: Joi.string().optional(),
   command: Joi.string().required(),
   schedule: scheduleSchema,
-  labels: Joi.array().optional(),
+  labels: Joi.array().optional().allow(null),
   sub_id: Joi.number().optional().allow(null),
   extra_schedules: Joi.array().optional().allow(null),
   task_before: Joi.string().optional().allow('').allow(null),
diff --git a/src/pages/crontab/modal.tsx b/src/pages/crontab/modal.tsx
index dfe9fa21..3313f458 100644
--- a/src/pages/crontab/modal.tsx
+++ b/src/pages/crontab/modal.tsx
@@ -28,6 +28,7 @@ const CronModal = ({
       const method = cron?.id ? 'put' : 'post';
       const payload = {
         ...values,
+        labels: values.labels || [],
         schedule:
           scheduleType !== ScheduleType.Normal
             ? scheduleTypeMap[scheduleType]
diff --git a/src/utils/http.tsx b/src/utils/http.tsx
index e45ab9c0..904fd076 100644
--- a/src/utils/http.tsx
+++ b/src/utils/http.tsx
@@ -9,8 +9,9 @@ import axios, {
   AxiosResponse,
   InternalAxiosRequestConfig,
 } from 'axios';
+import { getErrorDetails, ValidationErrorResponse } from './httpError';
 
-export interface IResponseData {
+export interface IResponseData extends ValidationErrorResponse {
   code?: number;
   data?: any;
   message?: string;
@@ -43,6 +44,7 @@ const errorHandler = function (
     const msg = error.response.data
       ? error.response.data.message || error.message
       : error.response.statusText;
+    const errorDetails = getErrorDetails(error.response.data);
     const responseStatus = error.response.status;
     if ([502, 504].includes(responseStatus)) {
       history.push('/error');
@@ -60,12 +62,10 @@ const errorHandler = function (
       msg &&
         notification.error({
           message: msg,
-          description: error.response?.data?.errors ? (
+          description: errorDetails.length ? (
             <>
-              {error.response?.data?.errors?.map((item: any) => (
-                <div>
-                  {item.message} ({item.value})
-                </div>
+              {errorDetails.map((detail, index) => (
+                <div key={`${index}-${detail}`}>{detail}</div>
               ))}
             </>
           ) : undefined,
diff --git a/src/utils/httpError.ts b/src/utils/httpError.ts
new file mode 100644
index 00000000..8e292d67
--- /dev/null
+++ b/src/utils/httpError.ts
@@ -0,0 +1,30 @@
+export interface ValidationErrorResponse {
+  errors?: Array<{ message?: string; value?: unknown }>;
+  validation?: Record<
+    string,
+    { source?: string; keys?: string[]; message?: string }
+  >;
+}
+
+export const getErrorDetails = (data?: ValidationErrorResponse) => {
+  const details =
+    data?.errors?.map((item) =>
+      item.value === undefined
+        ? item.message
+        : `${item.message} (${String(item.value)})`,
+    ) || [];
+
+  Object.values(data?.validation || {}).forEach((validation) => {
+    if (validation.keys?.length) {
+      validation.keys.forEach((key) => {
+        details.push(
+          validation.message ? `${key}: ${validation.message}` : key,
+        );
+      });
+    } else if (validation.message) {
+      details.push(validation.message);
+    }
+  });
+
+  return details.filter((detail): detail is string => Boolean(detail));
+};
diff --git a/test/back/cron-validation.test.cjs b/test/back/cron-validation.test.cjs
new file mode 100644
index 00000000..ddf5f9a1
--- /dev/null
+++ b/test/back/cron-validation.test.cjs
@@ -0,0 +1,45 @@
+const assert = require('node:assert/strict');
+const test = require('node:test');
+
+const configPath = require.resolve('../../back/config');
+require.cache[configPath] = {
+  id: configPath,
+  filename: configPath,
+  loaded: true,
+  exports: { __esModule: true, default: { logPath: '/ql/data/log' } },
+  children: [],
+  paths: [],
+};
+
+const { commonCronSchema } = require('../../back/validation/schedule');
+const { Joi } = require('celebrate');
+
+const schema = Joi.object(commonCronSchema);
+
+test('cron validation accepts leading-zero schedules and legacy null labels', () => {
+  const result = schema.validate({
+    name: 'legacy cron',
+    command: 'task legacy.js',
+    schedule: '01 7 * * *',
+    labels: null,
+  });
+
+  assert.equal(result.error, undefined);
+});
+
+test('cron validation identifies invalid fields', () => {
+  const result = schema.validate(
+    {
+      name: 'invalid cron',
+      command: 'task invalid.js',
+      schedule: '01 7 * * *',
+      allow_multiple_instances: '',
+    },
+    { abortEarly: false },
+  );
+
+  assert.deepEqual(
+    [...new Set(result.error.details.map((detail) => detail.path.join('.')))],
+    ['allow_multiple_instances'],
+  );
+});
diff --git a/test/front/http-error.test.cjs b/test/front/http-error.test.cjs
new file mode 100644
index 00000000..32cbd332
--- /dev/null
+++ b/test/front/http-error.test.cjs
@@ -0,0 +1,29 @@
+const assert = require('node:assert/strict');
+const test = require('node:test');
+
+const { getErrorDetails } = require('../../src/utils/httpError');
+
+test('validation errors include the failing field names', () => {
+  const details = getErrorDetails({
+    message: 'Validation failed',
+    validation: {
+      body: {
+        source: 'body',
+        keys: ['labels', 'allow_multiple_instances'],
+        message: 'request body contains invalid values',
+      },
+    },
+  });
+
+  assert.deepEqual(details, [
+    'labels: request body contains invalid values',
+    'allow_multiple_instances: request body contains invalid values',
+  ]);
+});
+
+test('existing API error details remain visible', () => {
+  assert.deepEqual(
+    getErrorDetails({ errors: [{ message: 'duplicate value', value: 'foo' }] }),
+    ['duplicate value (foo)'],
+  );
+});