diff --git a/src/shared/csv.ts b/src/shared/csv.ts
new file mode 100644
index 0000000..2008b1c
--- /dev/null
+++ b/src/shared/csv.ts
@@ -0,0 +1,29 @@
+/**
+ * CSV üretimi — Türkçe Excel ile uyumlu: noktalı virgül ayırıcı, ondalık virgül,
+ * UTF-8 BOM (Türkçe karakterler doğru açılır), CRLF satır sonu.
+ * Formül enjeksiyonuna karşı = + - @ ile başlayan metinler tek tırnakla etkisizleştirilir.
+ */
+export const CSV_SEPARATOR = ";";
+const BOM = "";
+
+export type CsvValue = string | number | null | undefined;
+
+function escapeCell(value: CsvValue): string {
+  if (value === null || value === undefined) return "";
+  let s = typeof value === "number" ? String(value) : value;
+  // Sayısal görünen değerler (ör. "-1250,50") olduğu gibi kalır; diğerleri formül olarak çalışmasın.
+  if (typeof value === "string" && /^[=+\-@\t\r]/.test(s) && !/^-?\d+(,\d+)?$/.test(s)) s = `'${s}`;
+  return /[";\r\n]/.test(s) ? `"${s.replace(/"/g, '""')}"` : s;
+}
+
+export function toCsv(header: readonly string[], rows: readonly (readonly CsvValue[])[]): string {
+  const lines = [header, ...rows].map((r) => r.map(escapeCell).join(CSV_SEPARATOR));
+  return BOM + lines.join("\r\n") + "\r\n";
+}
+
+/** Kuruş → "1250,50" (CSV'de sayı olarak okunur; binlik ayırıcı yok). */
+export function csvMoney(amountMinor: number): string {
+  const sign = amountMinor < 0 ? "-" : "";
+  const abs = Math.abs(amountMinor);
+  return `${sign}${Math.trunc(abs / 100)},${String(abs % 100).padStart(2, "0")}`;
+}
diff --git a/src/shared/schemas/transaction.ts b/src/shared/schemas/transaction.ts
new file mode 100644
index 0000000..e160eca
--- /dev/null
+++ b/src/shared/schemas/transaction.ts
@@ -0,0 +1,120 @@
+import { z } from "zod";
+import { tr } from "../../i18n/tr";
+import { parseMoney } from "../money";
+import { MAX_SPLITS, normalizeTags, TRANSACTION_TYPES } from "../transactions";
+
+const v = tr.validation;
+const t = tr.transactions.validation;
+const objectId = z.string().regex(/^[a-f0-9]{24}$/i, t.selectAccount);
+const optionalId = z
+  .string()
+  .regex(/^([a-f0-9]{24})?$/i)
+  .nullable()
+  .optional()
+  .transform((s) => (s ? s : null));
+
+/** Pozitif tutar ("1.250,50" → 125050). */
+const positiveMoney = z
+  .string()
+  .trim()
+  .transform((s, ctx) => {
+    const minor = parseMoney(s);
+    if (minor === null || minor <= 0) {
+      ctx.addIssue({ code: "custom", message: minor === null ? v.money : t.amountPositive });
+      return z.NEVER;
+    }
+    return minor;
+  });
+
+const splitSchema = z.object({
+  categoryId: objectId.refine(Boolean, t.selectCategory),
+  amount: positiveMoney,
+  note: z.string().trim().max(120).default(""),
+});
+
+/**
+ * İşlem formu (web + mobil). Kurallar:
+ * - transfer: hedef hesap zorunlu ve kaynaktan farklı; kategori/bölme yok.
+ * - gelir/gider: ya tek kategori ya da en az 2 kalemli bölme; kalemler toplamı = tutar.
+ */
+export const transactionFormSchema = z
+  .object({
+    type: z.enum(TRANSACTION_TYPES),
+    amount: positiveMoney,
+    date: z.string().regex(/^\d{4}-\d{2}-\d{2}$/, v.date),
+    accountId: objectId,
+    toAccountId: optionalId,
+    categoryId: optionalId,
+    splits: z.array(splitSchema).max(MAX_SPLITS).default([]),
+    payee: z.string().trim().max(80).default(""),
+    description: z.string().trim().max(500).default(""),
+    tags: z
+      .union([z.string(), z.array(z.string())])
+      .default("")
+      .transform((x) => normalizeTags(x)),
+  })
+  .superRefine((x, ctx) => {
+    if (x.type === "transfer") {
+      if (!x.toAccountId)
+        ctx.addIssue({ code: "custom", path: ["toAccountId"], message: t.selectToAccount });
+      else if (x.toAccountId === x.accountId)
+        ctx.addIssue({ code: "custom", path: ["toAccountId"], message: t.sameAccount });
+      return;
+    }
+    if (x.splits.length === 1) {
+      ctx.addIssue({ code: "custom", path: ["splits"], message: t.splitMin });
+    } else if (x.splits.length >= 2) {
+      const sum = x.splits.reduce((a, s) => a + s.amount, 0);
+      if (sum !== x.amount) ctx.addIssue({ code: "custom", path: ["splits"], message: t.splitSum });
+    } else if (!x.categoryId) {
+      ctx.addIssue({ code: "custom", path: ["categoryId"], message: t.selectCategory });
+    }
+  });
+
+export type TransactionFormInput = z.input<typeof transactionFormSchema>;
+export type TransactionForm = z.output<typeof transactionFormSchema>;
+
+/** Liste filtreleri (URL arama parametrelerinden). Geçersiz değerler yok sayılır. */
+export const transactionFilterSchema = z.object({
+  from: z
+    .string()
+    .regex(/^\d{4}-\d{2}-\d{2}$/)
+    .optional()
+    .catch(undefined),
+  to: z
+    .string()
+    .regex(/^\d{4}-\d{2}-\d{2}$/)
+    .optional()
+    .catch(undefined),
+  type: z.enum(TRANSACTION_TYPES).optional().catch(undefined),
+  hesap: z
+    .string()
+    .regex(/^[a-f0-9]{24}$/i)
+    .optional()
+    .catch(undefined),
+  kategori: z
+    .string()
+    .regex(/^[a-f0-9]{24}$/i)
+    .optional()
+    .catch(undefined),
+  kisi: z
+    .string()
+    .regex(/^[a-f0-9]{24}$/i)
+    .optional()
+    .catch(undefined),
+  durum: z.enum(["posted", "planned", "void"]).optional().catch(undefined),
+  min: z
+    .string()
+    .optional()
+    .catch(undefined)
+    .transform((s) => (s ? (parseMoney(s) ?? undefined) : undefined)),
+  max: z
+    .string()
+    .optional()
+    .catch(undefined)
+    .transform((s) => (s ? (parseMoney(s) ?? undefined) : undefined)),
+  etiket: z.string().trim().max(30).optional().catch(undefined),
+  q: z.string().trim().max(80).optional().catch(undefined),
+  sayfa: z.coerce.number().int().min(1).max(10_000).catch(1).default(1),
+});
+export type TransactionFilters = z.output<typeof transactionFilterSchema>;
diff --git a/src/shared/transactions.test.ts b/src/shared/transactions.test.ts
new file mode 100644
index 0000000..71e0317
--- /dev/null
+++ b/src/shared/transactions.test.ts
@@ -0,0 +1,132 @@
+import { describe, expect, it } from "vitest";
+import { toCsv, csvMoney } from "./csv";
+import { transactionFormSchema } from "./schemas/transaction";
+import { normalizeTags, transactionEffects } from "./transactions";
+
+const A = "a".repeat(24);
+const B = "b".repeat(24);
+const C1 = "c".repeat(24);
+const C2 = "d".repeat(24);
+
+describe("transactionEffects", () => {
+  it("gelir +, gider −, transfer kaynaktan − hedefe +", () => {
+    expect(
+      transactionEffects({ type: "income", status: "posted", amountMinor: 500, accountId: A }),
+    ).toEqual([{ accountId: A, deltaMinor: 500 }]);
+    expect(
+      transactionEffects({ type: "expense", status: "posted", amountMinor: 500, accountId: A }),
+    ).toEqual([{ accountId: A, deltaMinor: -500 }]);
+    expect(
+      transactionEffects({
+        type: "transfer",
+        status: "posted",
+        amountMinor: 500,
+        accountId: A,
+        toAccountId: B,
+      }),
+    ).toEqual([
+      { accountId: A, deltaMinor: -500 },
+      { accountId: B, deltaMinor: 500 },
+    ]);
+  });
+
+  it("planlı, iptal ve silinmiş işlemler etkisizdir", () => {
+    for (const x of [
+      { status: "planned" as const },
+      { status: "void" as const },
+      { status: "posted" as const, deleted: true },
+    ]) {
+      expect(transactionEffects({ type: "expense", amountMinor: 1, accountId: A, ...x })).toEqual(
+        [],
+      );
+    }
+  });
+});
+
+describe("normalizeTags", () => {
+  it("küçük harf, kırpma, tekrar yok, en fazla 10", () => {
+    expect(normalizeTags(" Market, İNDİRİM ,market,,#tatil")).toEqual([
+      "market",
+      "indirim",
+      "tatil",
+    ]);
+    expect(normalizeTags(Array.from({ length: 15 }, (_, i) => `e${i}`))).toHaveLength(10);
+  });
+});
+
+describe("transactionFormSchema", () => {
+  const base = { type: "expense", amount: "1.200,00", date: "2026-11-05", accountId: A };
+
+  it("tek kategorili gideri kabul eder ve tutarı kuruşa çevirir", () => {
+    const r = transactionFormSchema.parse({ ...base, categoryId: C1, tags: "ev, Ev" });
+    expect(r.amount).toBe(120000);
+    expect(r.categoryId).toBe(C1);
+    expect(r.tags).toEqual(["ev"]);
+    expect(r.splits).toEqual([]);
+  });
+
+  it("kategorisiz ve bölmesiz gideri reddeder", () => {
+    expect(transactionFormSchema.safeParse(base).success).toBe(false);
+  });
+
+  it("bölünmüş işlemde kalem toplamı tutara eşit olmalı", () => {
+    const ok = transactionFormSchema.safeParse({
+      ...base,
+      splits: [
+        { categoryId: C1, amount: "800" },
+        { categoryId: C2, amount: "250" },
+        { categoryId: C1, amount: "150,00" },
+      ],
+    });
+    expect(ok.success).toBe(true);
+    const bad = transactionFormSchema.safeParse({
+      ...base,
+      splits: [
+        { categoryId: C1, amount: "800" },
+        { categoryId: C2, amount: "250" },
+      ],
+    });
+    expect(bad.success).toBe(false);
+    expect(bad.error?.issues[0]?.path).toEqual(["splits"]);
+    const single = transactionFormSchema.safeParse({
+      ...base,
+      splits: [{ categoryId: C1, amount: "1200" }],
+    });
+    expect(single.success).toBe(false);
+  });
+
+  it("transfer: hedef zorunlu, kaynaktan farklı", () => {
+    expect(transactionFormSchema.safeParse({ ...base, type: "transfer" }).success).toBe(false);
+    expect(
+      transactionFormSchema.safeParse({ ...base, type: "transfer", toAccountId: A }).success,
+    ).toBe(false);
+    expect(
+      transactionFormSchema.safeParse({ ...base, type: "transfer", toAccountId: B }).success,
+    ).toBe(true);
+  });
+
+  it("sıfır, negatif ve geçersiz tutarı reddeder", () => {
+    for (const amount of ["0", "-5", "abc", ""]) {
+      expect(
+        transactionFormSchema.safeParse({ ...base, categoryId: C1, amount }).success,
+        amount,
+      ).toBe(false);
+    }
+  });
+});
+
+describe("CSV", () => {
+  it("BOM, noktalı virgül, kaçış ve formül enjeksiyonu koruması", () => {
+    const csv = toCsv(
+      ["A", "B"],
+      [
+        ["x;y", '"tırnak"'],
+        ["=HYPERLINK(1)", csvMoney(-125050)],
+      ],
+    );
+    expect(csv.startsWith("")).toBe(true);
+    expect(csv).toContain('"x;y";"""tırnak"""');
+    expect(csv).toContain("'=HYPERLINK(1);-1250,50");
+    expect(csv.endsWith("\r\n")).toBe(true);
+  });
+});
diff --git a/src/shared/transactions.ts b/src/shared/transactions.ts
new file mode 100644
index 0000000..a62e0ce
--- /dev/null
+++ b/src/shared/transactions.ts
@@ -0,0 +1,53 @@
+/** İşlem türleri ve durumları (Bölüm 6.3). */
+export const TRANSACTION_TYPES = ["expense", "income", "transfer"] as const;
+export type TransactionType = (typeof TRANSACTION_TYPES)[number];
+
+/** planned: Faz 7 (planlı işlemler) · posted: gerçekleşti · void: iptal (bakiyeyi etkilemez). */
+export const TRANSACTION_STATUSES = ["planned", "posted", "void"] as const;
+export type TransactionStatus = (typeof TRANSACTION_STATUSES)[number];
+
+export const MAX_SPLITS = 20;
+export const MAX_TAGS = 10;
+
+export type EffectInput = {
+  type: TransactionType;
+  status: TransactionStatus;
+  amountMinor: number;
+  accountId: string;
+  toAccountId?: string | null;
+  deleted?: boolean;
+};
+
+/**
+ * İşlemin hesap bakiyelerine etkisi (kuruş). Tutar her zaman pozitiftir; işaret türden gelir:
+ * gelir +, gider −, transfer kaynaktan −, hedefe +. Planlı, iptal ve silinmiş işlemler etkisizdir.
+ * Kredi kartında gider borcu artırır (bakiye daha negatif), karta transfer borcu azaltır.
+ */
+export function transactionEffects(t: EffectInput): { accountId: string; deltaMinor: number }[] {
+  if (t.status !== "posted" || t.deleted) return [];
+  switch (t.type) {
+    case "income":
+      return [{ accountId: t.accountId, deltaMinor: t.amountMinor }];
+    case "expense":
+      return [{ accountId: t.accountId, deltaMinor: -t.amountMinor }];
+    case "transfer":
+      return t.toAccountId
+        ? [
+            { accountId: t.accountId, deltaMinor: -t.amountMinor },
+            { accountId: t.toAccountId, deltaMinor: t.amountMinor },
+          ]
+        : [];
+  }
+}
+
+/** "market, İndirim ,market" → ["market", "indirim"] (küçük harf, tekrar yok, en fazla 10). */
+export function normalizeTags(input: string | readonly string[]): string[] {
+  const parts = typeof input === "string" ? input.split(/[,#]/) : input;
+  const out: string[] = [];
+  for (const raw of parts) {
+    const tag = raw.trim().replace(/\s+/g, " ").toLocaleLowerCase("tr-TR").slice(0, 30);
+    if (tag && !out.includes(tag)) out.push(tag);
+    if (out.length >= MAX_TAGS) break;
+  }
+  return out;
+}