diff --git a/src/domain/index.ts b/src/domain/index.ts
index aec69f2..ab0b404 100644
--- a/src/domain/index.ts
+++ b/src/domain/index.ts
@@ -1 +1,11 @@
 export const DOMAIN_READY = true;
+
+export * from "./types.ts";
+export * from "./money.ts";
+export * from "./months.ts";
+export * from "./fx.ts";
+export * from "./allocation.ts";
+export * from "./charges.ts";
+export * from "./fold.ts";
+export * from "./views.ts";
+export * from "./seed.ts";
diff --git a/src/domain/seed.test.ts b/src/domain/seed.test.ts
new file mode 100644
index 0000000..891eaa2
--- /dev/null
+++ b/src/domain/seed.test.ts
@@ -0,0 +1,48 @@
+import { test, expect } from "bun:test";
+import { createSeedDataset, SCHEMA_VERSION, newId } from "./seed.ts";
+import { monthView } from "./views.ts";
+
+test("seeds exactly the three named posts, in order", () => {
+  const data = createSeedDataset("2026-09");
+  expect(data.posts.map((p) => p.name)).toEqual([
+    "Video Games",
+    "Food",
+    "Events and Social",
+  ]);
+  expect(data.posts.map((p) => p.order)).toEqual([0, 1, 2]);
+});
+
+test("seeded posts are active with a zero fixed standing rule", () => {
+  const data = createSeedDataset("2026-09");
+  for (const post of data.posts) {
+    expect(post.archived).toBe(false);
+    expect(post.standingRule).toEqual({
+      kind: "fixed",
+      amount: { amount: 0, currency: "DKK" },
+    });
+  }
+});
+
+test("the fold starts at the given month and DKK is the base currency", () => {
+  const data = createSeedDataset("2026-09");
+  expect(data.settings.foldStartMonth).toBe("2026-09");
+  expect(data.settings.baseCurrency).toBe("DKK");
+  expect(data.settings.schemaVersion).toBe(SCHEMA_VERSION);
+});
+
+test("seeds a month record with zero income and no purchases", () => {
+  const data = createSeedDataset("2026-09");
+  expect(data.months.map((m) => m.id)).toEqual(["2026-09"]);
+  expect(data.purchases).toEqual([]);
+});
+
+test("the seed dataset renders a valid month view", () => {
+  const view = monthView(createSeedDataset("2026-09"), "2026-09");
+  expect(view.rows).toHaveLength(3);
+  expect(view.income).toBe(0);
+  expect(view.unallocated).toBe(0);
+});
+
+test("newId returns distinct ids", () => {
+  expect(newId()).not.toBe(newId());
+});
diff --git a/src/domain/seed.ts b/src/domain/seed.ts
new file mode 100644
index 0000000..8c63473
--- /dev/null
+++ b/src/domain/seed.ts
@@ -0,0 +1,38 @@
+import type { Dataset, MonthId, Post } from "./types.ts";
+
+export const SCHEMA_VERSION = 1;
+
+const SEED_POST_NAMES = ["Video Games", "Food", "Events and Social"] as const;
+
+export function newId(): string {
+  return crypto.randomUUID();
+}
+
+/**
+ * The first-run dataset. Takes the start month as an argument because the
+ * domain layer must not read the ambient clock.
+ */
+export function createSeedDataset(startMonth: MonthId): Dataset {
+  const posts: Post[] = SEED_POST_NAMES.map((name, order) => ({
+    id: newId(),
+    name,
+    order,
+    archived: false,
+    currency: "DKK",
+    standingRule: { kind: "fixed", amount: { amount: 0, currency: "DKK" } },
+  }));
+
+  return {
+    settings: {
+      baseCurrency: "DKK",
+      foldStartMonth: startMonth,
+      schemaVersion: SCHEMA_VERSION,
+    },
+    fxRates: [],
+    posts,
+    months: [
+      { id: startMonth, income: { amount: 0, currency: "DKK" }, ruleOverrides: {} },
+    ],
+    purchases: [],
+  };
+}