diff --git a/ui/src/pages/Alerts/RuleEditor/ConditionStep.tsx b/ui/src/pages/Alerts/RuleEditor/ConditionStep.tsx
new file mode 100644
index 00000000..a22fe75a
--- /dev/null
+++ b/ui/src/pages/Alerts/RuleEditor/ConditionStep.tsx
@@ -0,0 +1,5 @@
+import type { FormState } from './form-state';
+
+export function ConditionStep({ form: _form, setForm: _setForm }: { form: FormState; setForm: (f: FormState) => void }) {
+  return <div>Condition step &mdash; TODO Task 21</div>;
+}
diff --git a/ui/src/pages/Alerts/RuleEditor/NotifyStep.tsx b/ui/src/pages/Alerts/RuleEditor/NotifyStep.tsx
new file mode 100644
index 00000000..59d4d853
--- /dev/null
+++ b/ui/src/pages/Alerts/RuleEditor/NotifyStep.tsx
@@ -0,0 +1,13 @@
+import type { FormState } from './form-state';
+
+export function NotifyStep({
+  form: _form,
+  setForm: _setForm,
+  ruleId: _ruleId,
+}: {
+  form: FormState;
+  setForm: (f: FormState) => void;
+  ruleId?: string;
+}) {
+  return <div>Notify step &mdash; TODO Task 23</div>;
+}
diff --git a/ui/src/pages/Alerts/RuleEditor/ReviewStep.tsx b/ui/src/pages/Alerts/RuleEditor/ReviewStep.tsx
new file mode 100644
index 00000000..6801e71a
--- /dev/null
+++ b/ui/src/pages/Alerts/RuleEditor/ReviewStep.tsx
@@ -0,0 +1,11 @@
+import type { FormState } from './form-state';
+
+export function ReviewStep({
+  form: _form,
+  setForm: _setForm,
+}: {
+  form: FormState;
+  setForm?: (f: FormState) => void;
+}) {
+  return <div>Review step &mdash; TODO Task 24</div>;
+}
diff --git a/ui/src/pages/Alerts/RuleEditor/RuleEditorWizard.tsx b/ui/src/pages/Alerts/RuleEditor/RuleEditorWizard.tsx
index 26c55fc7..84ab1605 100644
--- a/ui/src/pages/Alerts/RuleEditor/RuleEditorWizard.tsx
+++ b/ui/src/pages/Alerts/RuleEditor/RuleEditorWizard.tsx
@@ -1,3 +1,154 @@
+import { useEffect, useState } from 'react';
+import { useNavigate, useParams, useSearchParams } from 'react-router';
+import { Button, SectionHeader, useToast } from '@cameleer/design-system';
+import { PageLoader } from '../../../components/PageLoader';
+import {
+  useAlertRule,
+  useCreateAlertRule,
+  useUpdateAlertRule,
+} from '../../../api/queries/alertRules';
+import {
+  initialForm,
+  toRequest,
+  validateStep,
+  WIZARD_STEPS,
+  type FormState,
+  type WizardStep,
+} from './form-state';
+import { ScopeStep } from './ScopeStep';
+import { ConditionStep } from './ConditionStep';
+import { TriggerStep } from './TriggerStep';
+import { NotifyStep } from './NotifyStep';
+import { ReviewStep } from './ReviewStep';
+import { prefillFromPromotion } from './promotion-prefill';
+import css from './wizard.module.css';
+
+const STEP_LABELS: Record<WizardStep, string> = {
+  scope: '1. Scope',
+  condition: '2. Condition',
+  trigger: '3. Trigger',
+  notify: '4. Notify',
+  review: '5. Review',
+};
+
 export default function RuleEditorWizard() {
-  return <div>RuleEditorWizard — coming soon</div>;
+  const navigate = useNavigate();
+  const { id } = useParams<{ id?: string }>();
+  const [search] = useSearchParams();
+  const { toast } = useToast();
+
+  const isEdit = !!id;
+  const existingQuery = useAlertRule(isEdit ? id : undefined);
+
+  // Promotion prefill uses a separate query against the source env. In
+  // Plan 03 we reuse `useAlertRule` (current-env scoped); cross-env
+  // fetching is handled server-side in the promote query hook when wired.
+  const promoteFrom = search.get('promoteFrom') ?? undefined;
+  const promoteRuleId = search.get('ruleId') ?? undefined;
+  const sourceRuleQuery = useAlertRule(promoteFrom ? promoteRuleId : undefined);
+
+  const [step, setStep] = useState<WizardStep>('scope');
+  const [form, setForm] = useState<FormState | null>(null);
+
+  // Initialize form once the existing or source rule loads.
+  useEffect(() => {
+    if (form) return;
+    if (isEdit && existingQuery.data) {
+      setForm(initialForm(existingQuery.data));
+      return;
+    }
+    if (promoteFrom && sourceRuleQuery.data) {
+      setForm(prefillFromPromotion(sourceRuleQuery.data));
+      return;
+    }
+    if (!isEdit && !promoteFrom) {
+      setForm(initialForm());
+    }
+  }, [form, isEdit, existingQuery.data, promoteFrom, sourceRuleQuery.data]);
+
+  const create = useCreateAlertRule();
+  const update = useUpdateAlertRule(id ?? '');
+
+  if (!form) return <PageLoader />;
+
+  const idx = WIZARD_STEPS.indexOf(step);
+  const errors = validateStep(step, form);
+
+  const onNext = () => {
+    if (errors.length > 0) {
+      toast({ title: 'Fix validation errors before continuing', description: errors.join(' \u00b7 '), variant: 'error' });
+      return;
+    }
+    if (idx < WIZARD_STEPS.length - 1) setStep(WIZARD_STEPS[idx + 1]);
+  };
+  const onBack = () => {
+    if (idx > 0) setStep(WIZARD_STEPS[idx - 1]);
+  };
+
+  const onSave = async () => {
+    try {
+      if (isEdit) {
+        await update.mutateAsync(toRequest(form));
+        toast({ title: 'Rule updated', description: form.name, variant: 'success' });
+      } else {
+        await create.mutateAsync(toRequest(form));
+        toast({ title: 'Rule created', description: form.name, variant: 'success' });
+      }
+      navigate('/alerts/rules');
+    } catch (e) {
+      toast({ title: 'Save failed', description: String(e), variant: 'error' });
+    }
+  };
+
+  const body =
+    step === 'scope' ? (
+      <ScopeStep form={form} setForm={setForm} />
+    ) : step === 'condition' ? (
+      <ConditionStep form={form} setForm={setForm} />
+    ) : step === 'trigger' ? (
+      <TriggerStep form={form} setForm={setForm} ruleId={id} />
+    ) : step === 'notify' ? (
+      <NotifyStep form={form} setForm={setForm} ruleId={id} />
+    ) : (
+      <ReviewStep form={form} setForm={setForm} />
+    );
+
+  return (
+    <div className={css.wizard}>
+      <div className={css.header}>
+        <SectionHeader>{isEdit ? `Edit rule: ${form.name}` : 'New alert rule'}</SectionHeader>
+        {promoteFrom && (
+          <div className={css.promoteBanner}>
+            Promoting from <code>{promoteFrom}</code> &mdash; review and adjust, then save.
+          </div>
+        )}
+      </div>
+      <nav className={css.steps}>
+        {WIZARD_STEPS.map((s, i) => (
+          <button
+            key={s}
+            className={`${css.step} ${step === s ? css.stepActive : ''} ${i < idx ? css.stepDone : ''}`}
+            onClick={() => setStep(s)}
+          >
+            {STEP_LABELS[s]}
+          </button>
+        ))}
+      </nav>
+      <div className={css.stepBody}>{body}</div>
+      <div className={css.footer}>
+        <Button variant="secondary" onClick={onBack} disabled={idx === 0}>
+          Back
+        </Button>
+        {idx < WIZARD_STEPS.length - 1 ? (
+          <Button variant="primary" onClick={onNext}>
+            Next
+          </Button>
+        ) : (
+          <Button variant="primary" onClick={onSave} disabled={create.isPending || update.isPending}>
+            {isEdit ? 'Save changes' : 'Create rule'}
+          </Button>
+        )}
+      </div>
+    </div>
+  );
 }
diff --git a/ui/src/pages/Alerts/RuleEditor/ScopeStep.tsx b/ui/src/pages/Alerts/RuleEditor/ScopeStep.tsx
new file mode 100644
index 00000000..649457f0
--- /dev/null
+++ b/ui/src/pages/Alerts/RuleEditor/ScopeStep.tsx
@@ -0,0 +1,5 @@
+import type { FormState } from './form-state';
+
+export function ScopeStep({ form: _form, setForm: _setForm }: { form: FormState; setForm: (f: FormState) => void }) {
+  return <div>Scope step &mdash; TODO Task 20</div>;
+}
diff --git a/ui/src/pages/Alerts/RuleEditor/TriggerStep.tsx b/ui/src/pages/Alerts/RuleEditor/TriggerStep.tsx
new file mode 100644
index 00000000..7ab844be
--- /dev/null
+++ b/ui/src/pages/Alerts/RuleEditor/TriggerStep.tsx
@@ -0,0 +1,13 @@
+import type { FormState } from './form-state';
+
+export function TriggerStep({
+  form: _form,
+  setForm: _setForm,
+  ruleId: _ruleId,
+}: {
+  form: FormState;
+  setForm: (f: FormState) => void;
+  ruleId?: string;
+}) {
+  return <div>Trigger step &mdash; TODO Task 22</div>;
+}
diff --git a/ui/src/pages/Alerts/RuleEditor/form-state.test.ts b/ui/src/pages/Alerts/RuleEditor/form-state.test.ts
new file mode 100644
index 00000000..40e68df8
--- /dev/null
+++ b/ui/src/pages/Alerts/RuleEditor/form-state.test.ts
@@ -0,0 +1,50 @@
+import { describe, it, expect } from 'vitest';
+import { initialForm, toRequest, validateStep } from './form-state';
+
+describe('initialForm', () => {
+  it('defaults to env-wide ROUTE_METRIC with safe intervals', () => {
+    const f = initialForm();
+    expect(f.scopeKind).toBe('env');
+    expect(f.conditionKind).toBe('ROUTE_METRIC');
+    expect(f.evaluationIntervalSeconds).toBeGreaterThanOrEqual(5);
+    expect(f.enabled).toBe(true);
+  });
+});
+
+describe('toRequest', () => {
+  it('strips empty scope fields for env-wide rules', () => {
+    const f = initialForm();
+    f.name = 'test';
+    const req = toRequest(f);
+    const scope = (req.condition as unknown as { scope: Record<string, string | undefined> }).scope;
+    expect(scope.appSlug).toBeUndefined();
+    expect(scope.routeId).toBeUndefined();
+    expect(scope.agentId).toBeUndefined();
+  });
+
+  it('includes appSlug for app/route/agent scopes', () => {
+    const f = initialForm();
+    f.scopeKind = 'app';
+    f.appSlug = 'orders';
+    const req = toRequest(f);
+    const scope = (req.condition as unknown as { scope: Record<string, string | undefined> }).scope;
+    expect(scope.appSlug).toBe('orders');
+  });
+});
+
+describe('validateStep', () => {
+  it('flags blank name on scope step', () => {
+    expect(validateStep('scope', initialForm())).toContain('Name is required.');
+  });
+  it('flags app requirement for app-scope', () => {
+    const f = initialForm();
+    f.name = 'x';
+    f.scopeKind = 'app';
+    expect(validateStep('scope', f).some((e) => /App is required/.test(e))).toBe(true);
+  });
+  it('flags intervals below floor on trigger step', () => {
+    const f = initialForm();
+    f.evaluationIntervalSeconds = 1;
+    expect(validateStep('trigger', f).some((e) => /Evaluation interval/.test(e))).toBe(true);
+  });
+});
diff --git a/ui/src/pages/Alerts/RuleEditor/form-state.ts b/ui/src/pages/Alerts/RuleEditor/form-state.ts
new file mode 100644
index 00000000..e6cee874
--- /dev/null
+++ b/ui/src/pages/Alerts/RuleEditor/form-state.ts
@@ -0,0 +1,151 @@
+import type {
+  AlertRuleRequest,
+  AlertRuleResponse,
+  ConditionKind,
+  AlertCondition,
+} from '../../../api/queries/alertRules';
+
+export type WizardStep = 'scope' | 'condition' | 'trigger' | 'notify' | 'review';
+export const WIZARD_STEPS: WizardStep[] = ['scope', 'condition', 'trigger', 'notify', 'review'];
+
+export interface FormState {
+  name: string;
+  description: string;
+  severity: 'CRITICAL' | 'WARNING' | 'INFO';
+  enabled: boolean;
+
+  // Scope (radio: env-wide | app | route | agent)
+  scopeKind: 'env' | 'app' | 'route' | 'agent';
+  appSlug: string;
+  routeId: string;
+  agentId: string;
+
+  conditionKind: ConditionKind;
+  condition: Partial<AlertCondition>;
+
+  evaluationIntervalSeconds: number;
+  forDurationSeconds: number;
+  reNotifyMinutes: number;
+
+  notificationTitleTmpl: string;
+  notificationMessageTmpl: string;
+
+  webhooks: Array<{
+    outboundConnectionId: string;
+    bodyOverride: string;
+    headerOverrides: Array<{ key: string; value: string }>;
+  }>;
+
+  targets: Array<{ kind: 'USER' | 'GROUP' | 'ROLE'; targetId: string }>;
+}
+
+export function initialForm(existing?: AlertRuleResponse): FormState {
+  if (!existing) {
+    return {
+      name: '',
+      description: '',
+      severity: 'WARNING',
+      enabled: true,
+      scopeKind: 'env',
+      appSlug: '',
+      routeId: '',
+      agentId: '',
+      conditionKind: 'ROUTE_METRIC',
+      condition: { kind: 'ROUTE_METRIC' } as Partial<AlertCondition>,
+      evaluationIntervalSeconds: 60,
+      forDurationSeconds: 0,
+      reNotifyMinutes: 60,
+      notificationTitleTmpl: '{{rule.name}} is firing',
+      notificationMessageTmpl: 'Alert {{alert.id}} fired at {{alert.firedAt}}',
+      webhooks: [],
+      targets: [],
+    };
+  }
+  const scope = ((existing.condition as { scope?: { appSlug?: string; routeId?: string; agentId?: string } } | undefined)?.scope) ?? {};
+  const scopeKind: FormState['scopeKind'] = scope.agentId
+    ? 'agent'
+    : scope.routeId
+      ? 'route'
+      : scope.appSlug
+        ? 'app'
+        : 'env';
+  return {
+    name: existing.name ?? '',
+    description: existing.description ?? '',
+    severity: (existing.severity ?? 'WARNING') as FormState['severity'],
+    enabled: existing.enabled ?? true,
+    scopeKind,
+    appSlug: scope.appSlug ?? '',
+    routeId: scope.routeId ?? '',
+    agentId: scope.agentId ?? '',
+    conditionKind: (existing.conditionKind ?? 'ROUTE_METRIC') as ConditionKind,
+    condition: (existing.condition ?? { kind: existing.conditionKind }) as Partial<AlertCondition>,
+    evaluationIntervalSeconds: existing.evaluationIntervalSeconds ?? 60,
+    forDurationSeconds: existing.forDurationSeconds ?? 0,
+    reNotifyMinutes: existing.reNotifyMinutes ?? 60,
+    notificationTitleTmpl: existing.notificationTitleTmpl ?? '{{rule.name}} is firing',
+    notificationMessageTmpl: existing.notificationMessageTmpl ?? 'Alert {{alert.id}} fired at {{alert.firedAt}}',
+    webhooks: (existing.webhooks ?? []).map((w) => ({
+      outboundConnectionId: (w.outboundConnectionId ?? '') as string,
+      bodyOverride: w.bodyOverride ?? '',
+      headerOverrides: Object.entries((w.headerOverrides ?? {}) as Record<string, string>)
+        .map(([key, value]) => ({ key, value })),
+    })),
+    targets: (existing.targets ?? []).map((t) => ({
+      kind: (t.kind ?? 'USER') as 'USER' | 'GROUP' | 'ROLE',
+      targetId: t.targetId ?? '',
+    })),
+  };
+}
+
+export function toRequest(f: FormState): AlertRuleRequest {
+  const scope: Record<string, string | undefined> = {};
+  if (f.scopeKind === 'app' || f.scopeKind === 'route' || f.scopeKind === 'agent') scope.appSlug = f.appSlug || undefined;
+  if (f.scopeKind === 'route') scope.routeId = f.routeId || undefined;
+  if (f.scopeKind === 'agent') scope.agentId = f.agentId || undefined;
+
+  const condition = { ...(f.condition as Record<string, unknown>), kind: f.conditionKind, scope } as unknown as AlertCondition;
+
+  return {
+    name: f.name,
+    description: f.description || undefined,
+    severity: f.severity,
+    enabled: f.enabled,
+    conditionKind: f.conditionKind,
+    condition,
+    evaluationIntervalSeconds: f.evaluationIntervalSeconds,
+    forDurationSeconds: f.forDurationSeconds,
+    reNotifyMinutes: f.reNotifyMinutes,
+    notificationTitleTmpl: f.notificationTitleTmpl,
+    notificationMessageTmpl: f.notificationMessageTmpl,
+    webhooks: f.webhooks.map((w) => ({
+      outboundConnectionId: w.outboundConnectionId,
+      bodyOverride: w.bodyOverride || undefined,
+      headerOverrides: Object.fromEntries(w.headerOverrides.filter((h) => h.key.trim()).map((h) => [h.key.trim(), h.value])),
+    })),
+    targets: f.targets.map((t) => ({ kind: t.kind, targetId: t.targetId })),
+  } as AlertRuleRequest;
+}
+
+export function validateStep(step: WizardStep, f: FormState): string[] {
+  const errs: string[] = [];
+  if (step === 'scope') {
+    if (!f.name.trim()) errs.push('Name is required.');
+    if (f.scopeKind !== 'env' && !f.appSlug.trim()) errs.push('App is required for app/route/agent scope.');
+    if (f.scopeKind === 'route' && !f.routeId.trim()) errs.push('Route id is required for route scope.');
+    if (f.scopeKind === 'agent' && !f.agentId.trim()) errs.push('Agent id is required for agent scope.');
+  }
+  if (step === 'condition') {
+    if (!f.conditionKind) errs.push('Condition kind is required.');
+  }
+  if (step === 'trigger') {
+    if (f.evaluationIntervalSeconds < 5) errs.push('Evaluation interval must be \u2265 5 s.');
+    if (f.forDurationSeconds < 0) errs.push('For-duration must be \u2265 0.');
+    if (f.reNotifyMinutes < 0) errs.push('Re-notify cadence must be \u2265 0.');
+  }
+  if (step === 'notify') {
+    if (!f.notificationTitleTmpl.trim()) errs.push('Notification title template is required.');
+    if (!f.notificationMessageTmpl.trim()) errs.push('Notification message template is required.');
+  }
+  return errs;
+}
diff --git a/ui/src/pages/Alerts/RuleEditor/promotion-prefill.ts b/ui/src/pages/Alerts/RuleEditor/promotion-prefill.ts
new file mode 100644
index 00000000..4f3ec43d
--- /dev/null
+++ b/ui/src/pages/Alerts/RuleEditor/promotion-prefill.ts
@@ -0,0 +1,15 @@
+import { initialForm, type FormState } from './form-state';
+import type { AlertRuleResponse } from '../../../api/queries/alertRules';
+
+/**
+ * Prefill the wizard form from a source rule being promoted from another env.
+ *
+ * Task 19 scaffolding: reuses the edit-prefill path and renames the rule.
+ * Task 24 rewrites this to compute scope-adjustment warnings and return
+ * `{ form, warnings }`.
+ */
+export function prefillFromPromotion(source: AlertRuleResponse): FormState {
+  const f = initialForm(source);
+  f.name = `${source.name ?? 'rule'} (copy)`;
+  return f;
+}
diff --git a/ui/src/pages/Alerts/RuleEditor/wizard.module.css b/ui/src/pages/Alerts/RuleEditor/wizard.module.css
new file mode 100644
index 00000000..4dfd103f
--- /dev/null
+++ b/ui/src/pages/Alerts/RuleEditor/wizard.module.css
@@ -0,0 +1,57 @@
+.wizard {
+  padding: 16px;
+  display: flex;
+  flex-direction: column;
+  gap: 16px;
+}
+
+.header {
+  display: flex;
+  justify-content: space-between;
+  align-items: center;
+  gap: 12px;
+  flex-wrap: wrap;
+}
+
+.promoteBanner {
+  padding: 8px 12px;
+  background: var(--amber-bg, rgba(255, 180, 0, 0.12));
+  border: 1px solid var(--amber);
+  border-radius: 6px;
+  font-size: 13px;
+}
+
+.steps {
+  display: flex;
+  gap: 8px;
+  border-bottom: 1px solid var(--border);
+  padding-bottom: 8px;
+}
+
+.step {
+  background: none;
+  border: none;
+  padding: 8px 12px;
+  border-bottom: 2px solid transparent;
+  cursor: pointer;
+  color: var(--muted);
+  font-size: 13px;
+}
+
+.stepActive {
+  color: var(--fg);
+  border-bottom-color: var(--accent);
+}
+
+.stepDone {
+  color: var(--fg);
+}
+
+.stepBody {
+  min-height: 320px;
+}
+
+.footer {
+  display: flex;
+  justify-content: space-between;
+}