diff --git a/ui/src/api/client.ts b/ui/src/api/client.ts
new file mode 100644
index 0000000..c7b9514
--- /dev/null
+++ b/ui/src/api/client.ts
@@ -0,0 +1,46 @@
+import { useAuthStore } from '../auth/auth-store';
+
+const API_BASE = '/api';
+
+async function apiFetch<T>(path: string, options: RequestInit = {}): Promise<T> {
+  const token = useAuthStore.getState().accessToken;
+  const headers: Record<string, string> = {
+    ...(options.headers as Record<string, string> || {}),
+  };
+  if (token) {
+    headers['Authorization'] = `Bearer ${token}`;
+  }
+  if (!headers['Content-Type'] && !(options.body instanceof FormData)) {
+    headers['Content-Type'] = 'application/json';
+  }
+
+  const response = await fetch(`${API_BASE}${path}`, { ...options, headers });
+
+  if (response.status === 401) {
+    useAuthStore.getState().logout();
+    window.location.href = '/login';
+    throw new Error('Unauthorized');
+  }
+
+  if (!response.ok) {
+    const text = await response.text();
+    throw new Error(`API error ${response.status}: ${text}`);
+  }
+
+  if (response.status === 204) return undefined as T;
+  return response.json();
+}
+
+export const api = {
+  get: <T>(path: string) => apiFetch<T>(path),
+  post: <T>(path: string, body?: unknown) =>
+    apiFetch<T>(path, {
+      method: 'POST',
+      body: body instanceof FormData ? body : JSON.stringify(body),
+    }),
+  patch: <T>(path: string, body: unknown) =>
+    apiFetch<T>(path, { method: 'PATCH', body: JSON.stringify(body) }),
+  put: <T>(path: string, body: FormData) =>
+    apiFetch<T>(path, { method: 'PUT', body }),
+  delete: <T>(path: string) => apiFetch<T>(path, { method: 'DELETE' }),
+};
diff --git a/ui/src/api/hooks.ts b/ui/src/api/hooks.ts
new file mode 100644
index 0000000..01ad1a8
--- /dev/null
+++ b/ui/src/api/hooks.ts
@@ -0,0 +1,185 @@
+import { useQuery, useMutation, useQueryClient } from '@tanstack/react-query';
+import { api } from './client';
+import type {
+  TenantResponse, EnvironmentResponse, AppResponse,
+  DeploymentResponse, LicenseResponse, AgentStatusResponse,
+  ObservabilityStatusResponse, LogEntry,
+} from '../types/api';
+
+// Tenant
+export function useTenant(tenantId: string) {
+  return useQuery({
+    queryKey: ['tenant', tenantId],
+    queryFn: () => api.get<TenantResponse>(`/tenants/${tenantId}`),
+    enabled: !!tenantId,
+  });
+}
+
+// License
+export function useLicense(tenantId: string) {
+  return useQuery({
+    queryKey: ['license', tenantId],
+    queryFn: () => api.get<LicenseResponse>(`/tenants/${tenantId}/license`),
+    enabled: !!tenantId,
+  });
+}
+
+// Environments
+export function useEnvironments(tenantId: string) {
+  return useQuery({
+    queryKey: ['environments', tenantId],
+    queryFn: () => api.get<EnvironmentResponse[]>(`/tenants/${tenantId}/environments`),
+    enabled: !!tenantId,
+  });
+}
+
+export function useCreateEnvironment(tenantId: string) {
+  const qc = useQueryClient();
+  return useMutation({
+    mutationFn: (data: { slug: string; displayName: string }) =>
+      api.post<EnvironmentResponse>(`/tenants/${tenantId}/environments`, data),
+    onSuccess: () => qc.invalidateQueries({ queryKey: ['environments', tenantId] }),
+  });
+}
+
+export function useUpdateEnvironment(tenantId: string, envId: string) {
+  const qc = useQueryClient();
+  return useMutation({
+    mutationFn: (data: { displayName: string }) =>
+      api.patch<EnvironmentResponse>(`/tenants/${tenantId}/environments/${envId}`, data),
+    onSuccess: () => qc.invalidateQueries({ queryKey: ['environments', tenantId] }),
+  });
+}
+
+export function useDeleteEnvironment(tenantId: string, envId: string) {
+  const qc = useQueryClient();
+  return useMutation({
+    mutationFn: () => api.delete(`/tenants/${tenantId}/environments/${envId}`),
+    onSuccess: () => qc.invalidateQueries({ queryKey: ['environments', tenantId] }),
+  });
+}
+
+// Apps
+export function useApps(environmentId: string) {
+  return useQuery({
+    queryKey: ['apps', environmentId],
+    queryFn: () => api.get<AppResponse[]>(`/environments/${environmentId}/apps`),
+    enabled: !!environmentId,
+  });
+}
+
+export function useApp(environmentId: string, appId: string) {
+  return useQuery({
+    queryKey: ['app', appId],
+    queryFn: () => api.get<AppResponse>(`/environments/${environmentId}/apps/${appId}`),
+    enabled: !!appId,
+  });
+}
+
+export function useCreateApp(environmentId: string) {
+  const qc = useQueryClient();
+  return useMutation({
+    mutationFn: (formData: FormData) =>
+      api.post<AppResponse>(`/environments/${environmentId}/apps`, formData),
+    onSuccess: () => qc.invalidateQueries({ queryKey: ['apps', environmentId] }),
+  });
+}
+
+export function useDeleteApp(environmentId: string, appId: string) {
+  const qc = useQueryClient();
+  return useMutation({
+    mutationFn: () => api.delete(`/environments/${environmentId}/apps/${appId}`),
+    onSuccess: () => qc.invalidateQueries({ queryKey: ['apps', environmentId] }),
+  });
+}
+
+export function useUpdateRouting(environmentId: string, appId: string) {
+  const qc = useQueryClient();
+  return useMutation({
+    mutationFn: (data: { exposedPort: number | null }) =>
+      api.patch<AppResponse>(`/environments/${environmentId}/apps/${appId}/routing`, data),
+    onSuccess: () => qc.invalidateQueries({ queryKey: ['app', appId] }),
+  });
+}
+
+// Deployments
+export function useDeploy(appId: string) {
+  const qc = useQueryClient();
+  return useMutation({
+    mutationFn: () => api.post<DeploymentResponse>(`/apps/${appId}/deploy`),
+    onSuccess: () => qc.invalidateQueries({ queryKey: ['deployments', appId] }),
+  });
+}
+
+export function useDeployments(appId: string) {
+  return useQuery({
+    queryKey: ['deployments', appId],
+    queryFn: () => api.get<DeploymentResponse[]>(`/apps/${appId}/deployments`),
+    enabled: !!appId,
+  });
+}
+
+export function useDeployment(appId: string, deploymentId: string) {
+  return useQuery({
+    queryKey: ['deployment', deploymentId],
+    queryFn: () => api.get<DeploymentResponse>(`/apps/${appId}/deployments/${deploymentId}`),
+    enabled: !!deploymentId,
+    refetchInterval: (query) => {
+      const status = query.state.data?.observedStatus;
+      return status === 'BUILDING' || status === 'STARTING' ? 3000 : false;
+    },
+  });
+}
+
+export function useStop(appId: string) {
+  const qc = useQueryClient();
+  return useMutation({
+    mutationFn: () => api.post<DeploymentResponse>(`/apps/${appId}/stop`),
+    onSuccess: () => {
+      qc.invalidateQueries({ queryKey: ['deployments', appId] });
+      qc.invalidateQueries({ queryKey: ['app'] });
+    },
+  });
+}
+
+export function useRestart(appId: string) {
+  const qc = useQueryClient();
+  return useMutation({
+    mutationFn: () => api.post<DeploymentResponse>(`/apps/${appId}/restart`),
+    onSuccess: () => qc.invalidateQueries({ queryKey: ['deployments', appId] }),
+  });
+}
+
+// Observability
+export function useAgentStatus(appId: string) {
+  return useQuery({
+    queryKey: ['agent-status', appId],
+    queryFn: () => api.get<AgentStatusResponse>(`/apps/${appId}/agent-status`),
+    enabled: !!appId,
+    refetchInterval: 15_000,
+  });
+}
+
+export function useObservabilityStatus(appId: string) {
+  return useQuery({
+    queryKey: ['observability-status', appId],
+    queryFn: () => api.get<ObservabilityStatusResponse>(`/apps/${appId}/observability-status`),
+    enabled: !!appId,
+    refetchInterval: 30_000,
+  });
+}
+
+export function useLogs(appId: string, params?: { since?: string; limit?: number; stream?: string }) {
+  return useQuery({
+    queryKey: ['logs', appId, params],
+    queryFn: () => {
+      const qs = new URLSearchParams();
+      if (params?.since) qs.set('since', params.since);
+      if (params?.limit) qs.set('limit', String(params.limit));
+      if (params?.stream) qs.set('stream', params.stream);
+      const query = qs.toString();
+      return api.get<LogEntry[]>(`/apps/${appId}/logs${query ? `?${query}` : ''}`);
+    },
+    enabled: !!appId,
+  });
+}