diff --git a/src/api/client.test.ts b/src/api/client.test.ts
new file mode 100644
index 0000000..3118c47
--- /dev/null
+++ b/src/api/client.test.ts
@@ -0,0 +1,15 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { apiGet } from "./client";
+import { NetWorthSchema } from "./schemas";
+beforeEach(() => vi.restoreAllMocks());
+describe("apiGet", () => {
+  it("fetches and validates", async () => {
+    vi.stubGlobal("fetch", vi.fn(async () => new Response(JSON.stringify({ assets: "1", liabilities: "0", total: "1" }), { status: 200 })));
+    const nw = await apiGet("/networth", NetWorthSchema);
+    expect(nw.total).toBe("1");
+  });
+  it("throws on http error", async () => {
+    vi.stubGlobal("fetch", vi.fn(async () => new Response("nope", { status: 401 })));
+    await expect(apiGet("/networth", NetWorthSchema)).rejects.toThrow();
+  });
+});
diff --git a/src/api/client.ts b/src/api/client.ts
new file mode 100644
index 0000000..9373a14
--- /dev/null
+++ b/src/api/client.ts
@@ -0,0 +1,39 @@
+import { z } from "zod";
+
+export class ApiError extends Error {
+  constructor(
+    public status: number,
+    msg: string,
+  ) {
+    super(msg);
+  }
+}
+
+async function req(method: string, path: string, body?: unknown): Promise<unknown> {
+  const res = await fetch(`/api/v1${path}`, {
+    method,
+    credentials: "same-origin",
+    headers: body === undefined ? undefined : { "Content-Type": "application/json" },
+    body: body === undefined ? undefined : JSON.stringify(body),
+  });
+  if (res.status === 401) {
+    if (typeof window !== "undefined") window.location.href = "/login";
+    throw new ApiError(401, "unauthorized");
+  }
+  if (!res.ok) throw new ApiError(res.status, await res.text());
+  return res.status === 204 ? null : res.json();
+}
+
+export async function apiGet<T>(path: string, schema: z.ZodType<T>): Promise<T> {
+  return schema.parse(await req("GET", path));
+}
+
+export async function apiSend<T>(
+  method: "POST" | "PUT" | "DELETE",
+  path: string,
+  body?: unknown,
+  schema?: z.ZodType<T>,
+): Promise<T | null> {
+  const data = await req(method, path, body);
+  return schema ? schema.parse(data) : (data as T);
+}
diff --git a/src/api/hooks/mutations.ts b/src/api/hooks/mutations.ts
new file mode 100644
index 0000000..1617615
--- /dev/null
+++ b/src/api/hooks/mutations.ts
@@ -0,0 +1,205 @@
+import { useMutation, useQueryClient } from "@tanstack/react-query";
+import { apiSend } from "../client";
+import { keys } from "../keys";
+import {
+  BudgetSchema,
+  SettingsSchema,
+  LendingSchema,
+  RevalueResultSchema,
+  SubscriptionSchema,
+} from "../schemas";
+
+// --- transactions ---
+
+export const useCategorize = () => {
+  const qc = useQueryClient();
+  return useMutation({
+    mutationFn: (b: { matchKey: string; category: string; kind?: "income" | "expense" }) =>
+      apiSend("POST", "/transactions/categorize", b),
+    onSuccess: () => {
+      qc.invalidateQueries({ queryKey: ["transactions"] });
+      qc.invalidateQueries({ queryKey: ["analyze"] });
+      qc.invalidateQueries({ queryKey: keys.budget });
+    },
+  });
+};
+
+export const useRenameTxn = () => {
+  const qc = useQueryClient();
+  return useMutation({
+    mutationFn: (b: { matchKey: string; name: string }) => apiSend("POST", "/transactions/rename", b),
+    onSuccess: () => qc.invalidateQueries({ queryKey: ["transactions"] }),
+  });
+};
+
+export const useSetNote = () => {
+  const qc = useQueryClient();
+  return useMutation({
+    mutationFn: (b: { id: number; note: string }) => apiSend("PUT", `/transactions/${b.id}/note`, { note: b.note }),
+    onSuccess: () => qc.invalidateQueries({ queryKey: ["transactions"] }),
+  });
+};
+
+// --- budget ---
+
+export const usePutBudget = () => {
+  const qc = useQueryClient();
+  return useMutation({
+    mutationFn: (b: {
+      dayLimit: string;
+      weekLimit: string;
+      monthLimit: string;
+      plannedIncomeManual: string;
+      categories: { name: string; day: string; week: string; month: string }[];
+    }) => apiSend("PUT", "/budget", b, BudgetSchema),
+    onSuccess: () => qc.invalidateQueries({ queryKey: keys.budget }),
+  });
+};
+
+// --- settings ---
+
+export const useSaveSettings = () => {
+  const qc = useQueryClient();
+  return useMutation({
+    mutationFn: (b: {
+      holderName: string;
+      employer: string;
+      salaryKeywords: string[];
+      payDays: number[];
+      ownAccounts: string[];
+      peerAccounts: string[];
+      hideAmounts?: boolean;
+    }) => apiSend("PUT", "/settings", b, SettingsSchema),
+    onSuccess: () => qc.invalidateQueries({ queryKey: keys.settings }),
+  });
+};
+
+// --- categories ---
+
+export const useCategoryMutations = () => {
+  const qc = useQueryClient();
+  const invalidate = () => {
+    qc.invalidateQueries({ queryKey: keys.categories });
+    qc.invalidateQueries({ queryKey: keys.budget });
+    qc.invalidateQueries({ queryKey: ["transactions"] });
+  };
+  const add = useMutation({
+    mutationFn: (b: { name: string; kind?: "income" | "expense"; parent?: string; icon?: string }) =>
+      apiSend("POST", "/categories", b),
+    onSuccess: invalidate,
+  });
+  const update = useMutation({
+    mutationFn: (b: { oldName: string; newName?: string; parent?: string | null; icon?: string | null }) =>
+      apiSend("PUT", "/categories", b),
+    onSuccess: invalidate,
+  });
+  const remove = useMutation({
+    mutationFn: (name: string) => apiSend("DELETE", `/categories?name=${encodeURIComponent(name)}`),
+    onSuccess: invalidate,
+  });
+  return { add, update, delete: remove };
+};
+
+// --- manual assets ---
+
+export const useManualAssetMutations = () => {
+  const qc = useQueryClient();
+  const invalidate = () => {
+    qc.invalidateQueries({ queryKey: keys.manualAssets });
+    qc.invalidateQueries({ queryKey: keys.networth });
+  };
+  const add = useMutation({
+    mutationFn: (b: {
+      name: string;
+      category?: string;
+      value: string;
+      acquiredValue?: string;
+      currency?: string;
+      condition?: string;
+      isLiability?: boolean;
+    }) => apiSend("POST", "/manual-assets", b),
+    onSuccess: invalidate,
+  });
+  const remove = useMutation({
+    mutationFn: (name: string) => apiSend("DELETE", `/manual-assets/${encodeURIComponent(name)}`),
+    onSuccess: invalidate,
+  });
+  const revalue = useMutation({
+    mutationFn: (name: string) => apiSend("POST", `/manual-assets/${encodeURIComponent(name)}/revalue`, undefined, RevalueResultSchema),
+    onSuccess: invalidate,
+  });
+  return { add, delete: remove, revalue };
+};
+
+// --- lending ---
+
+export const useLendingMutations = () => {
+  const qc = useQueryClient();
+  const invalidate = () => qc.invalidateQueries({ queryKey: keys.lending });
+  const create = useMutation({
+    mutationFn: (b: { person: string; amount: string; lentOn: string; dueOn?: string; note?: string; txnId?: number }) =>
+      apiSend("POST", "/lending", b, LendingSchema),
+    onSuccess: invalidate,
+  });
+  const remove = useMutation({
+    mutationFn: (id: number) => apiSend("DELETE", `/lending/${id}`),
+    onSuccess: invalidate,
+  });
+  const addRepayment = useMutation({
+    mutationFn: (b: { id: number; amount: string; paidOn: string; note?: string; txnId?: number }) =>
+      apiSend("POST", `/lending/${b.id}/repayments`, { amount: b.amount, paidOn: b.paidOn, note: b.note, txnId: b.txnId }, LendingSchema),
+    onSuccess: invalidate,
+  });
+  const deleteRepayment = useMutation({
+    mutationFn: (b: { id: number; repaymentId: number }) => apiSend("DELETE", `/lending/${b.id}/repayments/${b.repaymentId}`),
+    onSuccess: invalidate,
+  });
+  return { create, delete: remove, addRepayment, deleteRepayment };
+};
+
+// --- subscriptions ---
+
+export const useSubscriptionMutations = () => {
+  const qc = useQueryClient();
+  const invalidate = () => {
+    qc.invalidateQueries({ queryKey: keys.subscriptions });
+    qc.invalidateQueries({ queryKey: keys.budget });
+  };
+  const setSubscription = useMutation({
+    mutationFn: (b: { matchKey: string; name?: string; active: boolean }) => apiSend("POST", "/subscriptions", b),
+    onSuccess: invalidate,
+  });
+  const createManualSub = useMutation({
+    mutationFn: (b: { name: string; amount: string; category?: string; nextDue?: string }) =>
+      apiSend("POST", "/manual-subscriptions", b, SubscriptionSchema),
+    onSuccess: invalidate,
+  });
+  const deleteManualSub = useMutation({
+    mutationFn: (id: number) => apiSend("DELETE", `/manual-subscriptions/${id}`),
+    onSuccess: invalidate,
+  });
+  return { setSubscription, createManualSub, deleteManualSub };
+};
+
+// --- savings goals ---
+
+export const useSavingsGoalMutations = () => {
+  const qc = useQueryClient();
+  const invalidate = () => qc.invalidateQueries({ queryKey: keys.budget });
+  const post = useMutation({
+    mutationFn: (b: {
+      originalName?: string;
+      name: string;
+      target: string;
+      monthlyContribution?: string;
+      accountId?: number;
+      targetDate?: string;
+    }) => apiSend("POST", "/savings-goals", b, BudgetSchema),
+    onSuccess: invalidate,
+  });
+  const remove = useMutation({
+    mutationFn: (name: string) => apiSend("DELETE", `/savings-goals/${encodeURIComponent(name)}`, undefined, BudgetSchema),
+    onSuccess: invalidate,
+  });
+  return { post, delete: remove };
+};
diff --git a/src/api/hooks/reads.ts b/src/api/hooks/reads.ts
new file mode 100644
index 0000000..cd7bb10
--- /dev/null
+++ b/src/api/hooks/reads.ts
@@ -0,0 +1,125 @@
+import { useQuery } from "@tanstack/react-query";
+import { z } from "zod";
+import { apiGet } from "../client";
+import { keys } from "../keys";
+import {
+  NetWorthSchema,
+  AnalyzeSchema,
+  BudgetSchema,
+  TxnSchema,
+  CategorySchema,
+  SubscriptionSchema,
+  ManualAssetSchema,
+  LendingSchema,
+  SettingsSchema,
+  ConnectionSchema,
+  UserSchema,
+} from "../schemas";
+
+/** Local date (not UTC) as YYYY-MM-DD — dependency-free, matches the backend's
+ * `?from=&to=` parsing (time.Parse("2006-01-02", v)). */
+export function todayLocalDate(d: Date = new Date()): string {
+  const year = d.getFullYear();
+  const month = String(d.getMonth() + 1).padStart(2, "0");
+  const day = String(d.getDate()).padStart(2, "0");
+  return `${year}-${month}-${day}`;
+}
+
+export const useNetWorth = () =>
+  useQuery({ queryKey: keys.networth, queryFn: () => apiGet("/networth", NetWorthSchema) });
+
+export const useAnalyzeMonth = () =>
+  useQuery({ queryKey: keys.analyzeMonth, queryFn: () => apiGet("/analyze", AnalyzeSchema) });
+
+export const useAnalyzeToday = () => {
+  const d = todayLocalDate();
+  return useQuery({
+    queryKey: keys.analyzeToday(d),
+    queryFn: () => apiGet(`/analyze?from=${d}&to=${d}`, AnalyzeSchema),
+  });
+};
+
+export const useBudget = () => useQuery({ queryKey: keys.budget, queryFn: () => apiGet("/budget", BudgetSchema) });
+
+export interface TransactionsParams {
+  from?: string;
+  to?: string;
+  direction?: "income" | "expense";
+  category?: string;
+  account?: number | string;
+  limit?: number;
+}
+
+function txnQueryString(params?: TransactionsParams): string {
+  if (!params) return "";
+  const qs = new URLSearchParams();
+  if (params.from) qs.set("from", params.from);
+  if (params.to) qs.set("to", params.to);
+  if (params.direction) qs.set("direction", params.direction);
+  if (params.category) qs.set("category", params.category);
+  if (params.account !== undefined) qs.set("account", String(params.account));
+  if (params.limit !== undefined) qs.set("limit", String(params.limit));
+  const s = qs.toString();
+  return s ? `?${s}` : "";
+}
+
+const TransactionsResponseSchema = z.object({ transactions: z.array(TxnSchema) });
+
+export const useTransactions = (params?: TransactionsParams) => {
+  const qs = txnQueryString(params);
+  return useQuery({
+    queryKey: keys.transactions(qs),
+    queryFn: async () => (await apiGet(`/transactions${qs}`, TransactionsResponseSchema)).transactions,
+  });
+};
+
+const CategoriesResponseSchema = z.object({ categories: z.array(CategorySchema) });
+
+export const useCategories = () =>
+  useQuery({
+    queryKey: keys.categories,
+    queryFn: async () => (await apiGet("/categories", CategoriesResponseSchema)).categories,
+  });
+
+const SubscriptionsResponseSchema = z.object({
+  subscriptions: z.array(SubscriptionSchema),
+  bills: z.array(SubscriptionSchema),
+});
+
+export const useSubscriptions = () =>
+  useQuery({ queryKey: keys.subscriptions, queryFn: () => apiGet("/subscriptions", SubscriptionsResponseSchema) });
+
+const ManualAssetsResponseSchema = z.object({ manualAssets: z.array(ManualAssetSchema) });
+
+export const useManualAssets = () =>
+  useQuery({
+    queryKey: keys.manualAssets,
+    queryFn: async () => (await apiGet("/manual-assets", ManualAssetsResponseSchema)).manualAssets,
+  });
+
+const LendingResponseSchema = z.object({ entries: z.array(LendingSchema) });
+
+export const useLending = () =>
+  useQuery({
+    queryKey: keys.lending,
+    queryFn: async () => (await apiGet("/lending", LendingResponseSchema)).entries,
+  });
+
+export const useSettings = () =>
+  useQuery({ queryKey: keys.settings, queryFn: () => apiGet("/settings", SettingsSchema) });
+
+const ConnectionsResponseSchema = z.object({ connections: z.array(ConnectionSchema) });
+
+export const useConnections = () =>
+  useQuery({
+    queryKey: keys.connections,
+    queryFn: async () => (await apiGet("/connections", ConnectionsResponseSchema)).connections,
+  });
+
+const MeResponseSchema = z.object({ user: UserSchema });
+
+export const useMe = () =>
+  useQuery({
+    queryKey: keys.me,
+    queryFn: async () => (await apiGet("/me", MeResponseSchema)).user,
+  });
diff --git a/src/api/keys.ts b/src/api/keys.ts
new file mode 100644
index 0000000..9113483
--- /dev/null
+++ b/src/api/keys.ts
@@ -0,0 +1,14 @@
+export const keys = {
+  networth: ["networth"] as const,
+  analyzeMonth: ["analyze", "month"] as const,
+  analyzeToday: (d: string) => ["analyze", "today", d] as const,
+  budget: ["budget"] as const,
+  transactions: (p: string) => ["transactions", p] as const,
+  categories: ["categories"] as const,
+  subscriptions: ["subscriptions"] as const,
+  manualAssets: ["manualAssets"] as const,
+  lending: ["lending"] as const,
+  settings: ["settings"] as const,
+  connections: ["connections"] as const,
+  me: ["me"] as const,
+} as const;
diff --git a/src/api/queryClient.tsx b/src/api/queryClient.tsx
new file mode 100644
index 0000000..194c1f1
--- /dev/null
+++ b/src/api/queryClient.tsx
@@ -0,0 +1,22 @@
+"use client";
+
+import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
+import type { ReactNode } from "react";
+
+// Module-level singleton: one QueryClient shared across the app (client-side
+// only — Next's RSC boundary means this module is only ever instantiated in
+// the browser via the "use client" directive above).
+const queryClient = new QueryClient({
+  defaultOptions: {
+    queries: {
+      staleTime: 30_000,
+      retry: 1,
+    },
+  },
+});
+
+export function AppQueryProvider({ children }: { children: ReactNode }) {
+  return <QueryClientProvider client={queryClient}>{children}</QueryClientProvider>;
+}
+
+export { queryClient };