diff --git a/scripts/seed-demo.ts b/scripts/seed-demo.ts
new file mode 100644
index 0000000..8ffe196
--- /dev/null
+++ b/scripts/seed-demo.ts
@@ -0,0 +1,47 @@
+/**
+ * Fictional data (3 clients, 5 projects, ~60 days of time entries) for manual testing.
+ *   npx tsx scripts/seed-demo.ts --email vinicius3w@gmail.com --workspace "ASSERT Lab"            # dry-run (default)
+ *   npx tsx scripts/seed-demo.ts --email vinicius3w@gmail.com --workspace "ASSERT Lab" --apply     # writes
+ * The database comes from DATABASE_URL (use `read -s` to pass production's, see the PR). Idempotent: a workspace that
+ * already has the "demo" tag is skipped. Prints only the database host, never the connection string.
+ */
+import { and, eq, isNull, sql } from "drizzle-orm";
+import { getDb } from "@/db";
+import { users, workspaceMembers, workspaces } from "@/db/schema";
+import { getEnv } from "@/env";
+import { seedDemo } from "@/server/seed-demo";
+
+function arg(name: string) {
+  const i = process.argv.indexOf(`--${name}`);
+  return i >= 0 ? process.argv[i + 1] : undefined;
+}
+
+async function main() {
+  const email = arg("email")?.trim().toLowerCase();
+  const workspaceName = arg("workspace")?.trim();
+  const apply = process.argv.includes("--apply");
+  if (!email || !workspaceName) throw new Error('Usage: seed-demo.ts --email <e-mail> --workspace "<name>" [--apply]');
+
+  const db = getDb();
+  console.log(`Database host: ${new URL(getEnv().DATABASE_URL).host}`);
+  console.log(apply ? "Mode: APPLY (writes)" : "Mode: dry-run (nothing is written; pass --apply to write)");
+
+  const [user] = await db.select().from(users).where(and(sql`lower(${users.email}) = ${email}`, isNull(users.deletedAt)));
+  if (!user) throw new Error(`No active user with e-mail ${email}`);
+  const matches = await db
+    .select({ id: workspaces.id, name: workspaces.name, timezone: users.timezone })
+    .from(workspaces)
+    .innerJoin(workspaceMembers, eq(workspaceMembers.workspaceId, workspaces.id))
+    .innerJoin(users, eq(users.id, workspaceMembers.userId))
+    .where(and(eq(users.id, user.id), isNull(workspaceMembers.removedAt), isNull(workspaces.archivedAt), sql`lower(${workspaces.name}) = ${workspaceName.toLowerCase()}`));
+  if (matches.length !== 1) throw new Error(`Expected exactly one workspace named "${workspaceName}" for ${email}, found ${matches.length}`);
+
+  const result = await seedDemo(db, { workspaceId: matches[0].id, userId: user.id, timezone: matches[0].timezone, apply });
+  console.log(JSON.stringify({ workspace: matches[0].name, user: email, ...result }, null, 2));
+  if (result.skipped) console.log('Skipped: this workspace already has the "demo" tag.');
+}
+
+main().catch((e) => {
+  console.error(e instanceof Error ? e.message : e);
+  process.exit(1);
+});
diff --git a/src/server/seed-demo.test.ts b/src/server/seed-demo.test.ts
new file mode 100644
index 0000000..99c3231
--- /dev/null
+++ b/src/server/seed-demo.test.ts
@@ -0,0 +1,92 @@
+import { and, eq } from "drizzle-orm";
+import { beforeEach, describe, expect, it } from "vitest";
+import type { Db } from "@/db";
+import { organizations, projects, tags, timeEntries, timeEntryTags } from "@/db/schema";
+import { localDateString } from "@/lib/time";
+import { createTestDb, seedWorkspace, type TestDb } from "@/test/db";
+import { planDay, seedDemo } from "./seed-demo";
+
+const TZ = "America/Recife";
+const NOW = new Date("2026-10-09T15:00:00Z");
+
+describe("seedDemo", () => {
+  let db: TestDb;
+  let a: { workspaceId: string; userId: string };
+  let b: { workspaceId: string; userId: string };
+  const run = (apply: boolean, who = a) => seedDemo(db as unknown as Db, { ...who, timezone: TZ, today: NOW, apply });
+
+  beforeEach(async () => {
+    db = await createTestDb();
+    a = await seedWorkspace(db, "sa");
+    b = await seedWorkspace(db, "sb");
+  });
+
+  it("dry-run reports the plan and writes nothing", async () => {
+    const r = await run(false);
+    expect(r).toMatchObject({ applied: false, skipped: false, clients: 3, projects: 5 });
+    expect(r.entries).toBeGreaterThan(80);
+    expect(await db.select().from(organizations)).toHaveLength(0);
+    expect(await db.select().from(timeEntries)).toHaveLength(0);
+  });
+
+  it("applies: catalog, tagged entries, only weekdays before today, closed and non-overlapping", async () => {
+    const r = await run(true);
+    expect(r.applied).toBe(true);
+    const entries = await db.select().from(timeEntries).where(eq(timeEntries.workspaceId, a.workspaceId));
+    expect(entries).toHaveLength(r.entries);
+    const today = localDateString(NOW, TZ);
+    for (const e of entries) {
+      expect(e.endedAt).not.toBeNull();
+      expect(e.endedAt! > e.startedAt).toBe(true);
+      const day = localDateString(e.startedAt, TZ);
+      expect(day < today).toBe(true);
+      expect([0, 6]).not.toContain(new Date(`${day}T12:00:00Z`).getUTCDay());
+    }
+    const sorted = [...entries].sort((x, y) => x.startedAt.getTime() - y.startedAt.getTime());
+    sorted.slice(1).forEach((e, i) => expect(e.startedAt >= sorted[i].endedAt!).toBe(true));
+    expect(entries.some((e) => e.projectId === null)).toBe(true); // exercises the "without project" warning
+    expect(entries.some((e) => !e.isBillable)).toBe(true);
+    const demo = await db.select().from(tags).where(and(eq(tags.workspaceId, a.workspaceId), eq(tags.name, "demo")));
+    const tagged = await db.select().from(timeEntryTags).where(eq(timeEntryTags.tagId, demo[0].id));
+    expect(tagged).toHaveLength(r.entries);
+  });
+
+  it("is idempotent and stays inside the target workspace", async () => {
+    await run(true);
+    const again = await run(true);
+    expect(again.skipped).toBe(true);
+    expect(await db.select().from(timeEntries).where(eq(timeEntries.workspaceId, a.workspaceId))).toHaveLength((await run(false)).entries);
+    expect(await db.select().from(projects).where(eq(projects.workspaceId, b.workspaceId))).toHaveLength(0);
+    expect(await db.select().from(timeEntries).where(eq(timeEntries.workspaceId, b.workspaceId))).toHaveLength(0);
+  });
+
+  it("can seed a second workspace independently (same client names)", async () => {
+    await run(true);
+    expect((await run(true, b)).applied).toBe(true);
+    expect(await db.select().from(organizations)).toHaveLength(6);
+  });
+
+  it("recovers from a run that died before the marker tag, without duplicating entries", async () => {
+    const full = await run(true);
+    await db.delete(tags).where(and(eq(tags.workspaceId, a.workspaceId), eq(tags.name, "demo"))); // simulate the interrupted run
+    await run(true);
+    expect(await db.select().from(timeEntries).where(eq(timeEntries.workspaceId, a.workspaceId))).toHaveLength(full.entries);
+  });
+});
+
+describe("planDay", () => {
+  it("never overlaps, skips lunch and ends before 19:00", () => {
+    let seed = 1;
+    const rand = () => ((seed = (seed * 16807) % 2147483647) / 2147483647);
+    for (let i = 0; i < 200; i++) {
+      const slots = planDay("2026-10-05", rand);
+      expect(slots.length).toBeGreaterThanOrEqual(1);
+      slots.forEach((s, j) => {
+        expect(s.endMin).toBeGreaterThan(s.startMin);
+        expect(s.endMin).toBeLessThanOrEqual(19 * 60);
+        expect(s.startMin < 12 * 60 && s.endMin > 12 * 60).toBe(false);
+        if (j > 0) expect(s.startMin).toBeGreaterThanOrEqual(slots[j - 1].endMin);
+      });
+    }
+  });
+});
diff --git a/src/server/seed-demo.ts b/src/server/seed-demo.ts
new file mode 100644
index 0000000..19e2527
--- /dev/null
+++ b/src/server/seed-demo.ts
@@ -0,0 +1,180 @@
+import { and, eq } from "drizzle-orm";
+import type { Db } from "@/db";
+import { organizations, projectMembers, projects, tags, tasks, timeEntries, timeEntryTags, workspaceMembers } from "@/db/schema";
+import { addDays, localDateString, zonedTimeToUtc } from "@/lib/time";
+
+/** Fictional data for manual testing. Everything is tagged "demo"; client names end with " (demo)". */
+export const DEMO_TAG = "demo";
+
+const CLIENTS = [
+  {
+    name: "ASSERT Lab (demo)",
+    projects: [
+      { name: "Pesquisa em qualidade de software", color: "#8B5CF6", billable: false, tasks: ["Revisão de literatura", "Escrita de artigo", "Reunião de orientação"] },
+      { name: "Infraestrutura do laboratório", color: "#64748B", billable: false, tasks: ["Manutenção de servidores", "Documentação"] },
+    ],
+  },
+  {
+    name: "Acme Consultoria (demo)",
+    projects: [
+      { name: "Portal do cliente", color: "#3B82F6", billable: true, tasks: ["Levantamento de requisitos", "Desenvolvimento front-end", "Revisão de código", "Homologação"] },
+      { name: "Migração de dados", color: "#0EA5E9", billable: true, tasks: ["Mapeamento de tabelas", "Scripts de carga", "Validação"] },
+    ],
+  },
+  {
+    name: "Nova Energia (demo)",
+    projects: [{ name: "Painel de indicadores", color: "#10B981", billable: true, tasks: ["Modelagem dos dados", "Dashboards", "Treinamento da equipe"] }],
+  },
+] as const;
+
+const DESCRIPTIONS = ["Ajustes e correções", "Implementação", "Análise e planejamento", "Reunião de alinhamento", "Revisão", "Testes", "Documentação", "Pesquisa"];
+const TAGS = [DEMO_TAG, "reunião", "desenvolvimento", "pesquisa"];
+
+/** Small deterministic PRNG (mulberry32): the same seed always produces the same data. */
+function prng(seed: number) {
+  let a = seed >>> 0;
+  return () => {
+    a = (a + 0x6d2b79f5) >>> 0;
+    let t = a;
+    t = Math.imul(t ^ (t >>> 15), t | 1);
+    t ^= t + Math.imul(t ^ (t >>> 7), t | 61);
+    return ((t ^ (t >>> 14)) >>> 0) / 4294967296;
+  };
+}
+
+const hhmm = (minutes: number) => `${String(Math.floor(minutes / 60)).padStart(2, "0")}:${String(minutes % 60).padStart(2, "0")}`;
+
+type Slot = { date: string; startMin: number; endMin: number };
+
+/** 3 to 5 non-overlapping blocks per weekday, around lunch, between 08:00 and 19:00 local time. */
+export function planDay(date: string, rand: () => number): Slot[] {
+  const slots: Slot[] = [];
+  let cursor = 8 * 60 + Math.floor(rand() * 5) * 6;
+  const blocks = 3 + Math.floor(rand() * 3);
+  for (let i = 0; i < blocks; i++) {
+    const duration = 45 + Math.floor(rand() * 11) * 9; // 45..135 min
+    let end = cursor + duration;
+    if (cursor < 12 * 60 && end > 12 * 60) {
+      cursor = 13 * 60 + 30;
+      end = cursor + duration;
+    }
+    if (end > 19 * 60) break;
+    slots.push({ date, startMin: cursor, endMin: end });
+    cursor = end + 5 + Math.floor(rand() * 5) * 5;
+  }
+  return slots;
+}
+
+export type DemoPlan = { clients: number; projects: number; tasks: number; entries: number; hours: number };
+export type DemoResult = DemoPlan & { applied: boolean; skipped: boolean };
+
+const isWeekday = (date: string) => ![0, 6].includes(new Date(`${date}T12:00:00Z`).getUTCDay());
+
+export async function seedDemo(
+  db: Db,
+  { workspaceId, userId, timezone = "America/Recife", today = new Date(), days = 60, apply = false }: { workspaceId: string; userId: string; timezone?: string; today?: Date; days?: number; apply?: boolean },
+): Promise<DemoResult> {
+  const rand = prng(20261009);
+  const lastDay = addDays(localDateString(today, timezone), -1); // never today: no clash with a real running timer
+  const dates = Array.from({ length: days }, (_, i) => addDays(lastDay, -(days - 1 - i))).filter(isWeekday);
+
+  const projectList = CLIENTS.flatMap((c) => c.projects.map((p) => ({ client: c.name, ...p })));
+  const rows = dates.flatMap((date) =>
+    planDay(date, rand).map((slot) => {
+      const withoutProject = rand() < 0.06;
+      const project = projectList[Math.floor(rand() * projectList.length)];
+      const task = project.tasks[Math.floor(rand() * project.tasks.length)];
+      const description = DESCRIPTIONS[Math.floor(rand() * DESCRIPTIONS.length)];
+      const meeting = description.startsWith("Reunião");
+      return {
+        startedAt: zonedTimeToUtc(slot.date, hhmm(slot.startMin), timezone),
+        endedAt: zonedTimeToUtc(slot.date, hhmm(slot.endMin), timezone),
+        project: withoutProject ? null : project,
+        task: withoutProject ? null : task,
+        description: withoutProject ? "Triagem de e-mails" : description,
+        isBillable: !withoutProject && project.billable && !meeting,
+        tagNames: [DEMO_TAG, ...(meeting ? ["reunião"] : []), ...(!meeting && project.billable ? ["desenvolvimento"] : []), ...(project.name.startsWith("Pesquisa") ? ["pesquisa"] : [])],
+      };
+    }),
+  );
+  const plan: DemoPlan = {
+    clients: CLIENTS.length,
+    projects: projectList.length,
+    tasks: projectList.reduce((n, p) => n + p.tasks.length, 0),
+    entries: rows.length,
+    hours: Math.round((rows.reduce((s, r) => s + (r.endedAt.getTime() - r.startedAt.getTime()), 0) / 3_600_000) * 10) / 10,
+  };
+
+  const [already] = await db.select({ id: tags.id }).from(tags).where(and(eq(tags.workspaceId, workspaceId), eq(tags.name, DEMO_TAG)));
+  if (already) return { ...plan, applied: false, skipped: true };
+  if (!apply) return { ...plan, applied: false, skipped: false };
+
+  // neon-http has no interactive transactions: dependency order, each step one statement (safe to rerun after a failure
+  // because the "demo" tag is created last and its presence is what marks the workspace as seeded).
+  const orgRows = await db
+    .insert(organizations)
+    .values(CLIENTS.map((c) => ({ workspaceId, name: c.name })))
+    .onConflictDoUpdate({ target: [organizations.workspaceId, organizations.name], set: { isArchived: false } })
+    .returning();
+  const orgByName = new Map(orgRows.map((o) => [o.name, o.id]));
+
+  const projectRows = await db
+    .insert(projects)
+    .values(projectList.map((p) => ({ workspaceId, organizationId: orgByName.get(p.client)!, name: p.name, color: p.color })))
+    .onConflictDoUpdate({ target: [projects.organizationId, projects.name], set: { isArchived: false } })
+    .returning();
+  const projectByName = new Map(projectRows.map((p) => [p.name, p.id]));
+
+  const taskRows = await db
+    .insert(tasks)
+    .values(projectList.flatMap((p) => p.tasks.map((name) => ({ workspaceId, projectId: projectByName.get(p.name)!, name }))))
+    .onConflictDoUpdate({ target: [tasks.projectId, tasks.name], set: { isCompleted: false } })
+    .returning();
+  const taskKey = (projectId: string, name: string) => `${projectId}|${name}`;
+  const taskByKey = new Map(taskRows.map((t) => [taskKey(t.projectId, t.name), t.id]));
+
+  // Everyone who is already an active member of the workspace takes part in the demo projects.
+  const members = await db.select({ userId: workspaceMembers.userId }).from(workspaceMembers).where(eq(workspaceMembers.workspaceId, workspaceId));
+  await db
+    .insert(projectMembers)
+    .values(members.flatMap((m) => projectRows.map((p) => ({ workspaceId, projectId: p.id, userId: m.userId }))))
+    .onConflictDoNothing();
+
+  // A previous run may have died after inserting entries but before the marker tag: never insert the same entry twice.
+  const existing = await db.select({ startedAt: timeEntries.startedAt }).from(timeEntries).where(and(eq(timeEntries.workspaceId, workspaceId), eq(timeEntries.userId, userId)));
+  const taken = new Set(existing.map((e) => e.startedAt.getTime()));
+  const fresh = rows.filter((r) => !taken.has(r.startedAt.getTime()));
+  for (let i = 0; i < fresh.length; i += 100) {
+    const chunk = fresh.slice(i, i + 100);
+    await db.insert(timeEntries).values(
+      chunk.map((r) => {
+        const projectId = r.project ? projectByName.get(r.project.name)! : null;
+        return {
+          workspaceId,
+          userId,
+          projectId,
+          taskId: projectId && r.task ? taskByKey.get(taskKey(projectId, r.task))! : null,
+          description: r.description,
+          startedAt: r.startedAt,
+          endedAt: r.endedAt,
+          timezone,
+          isBillable: r.isBillable,
+        };
+      }),
+    );
+  }
+
+  // The "demo" tag is the marker of a finished seed: created after the entries, then attached to them.
+  await db.insert(tags).values(TAGS.map((name) => ({ workspaceId, name }))).onConflictDoNothing();
+  // Read them back: `returning()` would only list the new rows, and the workspace may already have tags such as "reunião".
+  const tagRows = await db.select().from(tags).where(eq(tags.workspaceId, workspaceId));
+  const tagId = new Map(tagRows.map((t) => [t.name, t.id]));
+  const created = await db.select({ id: timeEntries.id, startedAt: timeEntries.startedAt }).from(timeEntries).where(and(eq(timeEntries.workspaceId, workspaceId), eq(timeEntries.userId, userId)));
+  const idByStart = new Map(created.map((e) => [e.startedAt.getTime(), e.id]));
+  const links = rows.flatMap((r) => {
+    const entryId = idByStart.get(r.startedAt.getTime());
+    return entryId ? r.tagNames.map((n) => ({ timeEntryId: entryId, tagId: tagId.get(n)! })) : [];
+  });
+  for (let i = 0; i < links.length; i += 200) await db.insert(timeEntryTags).values(links.slice(i, i + 200)).onConflictDoNothing();
+  return { ...plan, applied: true, skipped: false };
+}