diff --git a/src/__tests__/planCategory.test.ts b/src/__tests__/planCategory.test.ts
new file mode 100644
index 0000000..483e91c
--- /dev/null
+++ b/src/__tests__/planCategory.test.ts
@@ -0,0 +1,86 @@
+import { describe, it, expect, afterAll } from "vitest";
+import prisma from "../config/database";
+import {
+  listPlanCategories,
+  createPlanCategory,
+  updatePlanCategory,
+  deactivatePlanCategory,
+  isCategoryKeyActive,
+  slugifyCategory,
+} from "../services/planCategory.service";
+
+const created: number[] = [];
+
+afterAll(async () => {
+  if (created.length) {
+    await prisma.plan_categories.deleteMany({ where: { id: { in: created } } });
+  }
+  await prisma.$disconnect();
+});
+
+describe("slugifyCategory", () => {
+  it("strips Czech diacritics and non-alphanumerics", () => {
+    expect(slugifyCategory("Cesta / Montáž")).toBe("cesta_montaz");
+    expect(slugifyCategory("Příprava")).toBe("priprava");
+  });
+});
+
+describe("plan category service", () => {
+  it("seeds are present and ordered", async () => {
+    const cats = await listPlanCategories(true);
+    const keys = cats.map((c) => c.key);
+    expect(keys).toContain("work");
+    expect(keys).toContain("other");
+  });
+
+  it("creates a category with a unique slug and next sort_order", async () => {
+    const res = await createPlanCategory({
+      label: "Test Kategorie ZZ",
+      color: "#123456",
+    });
+    if ("error" in res) throw new Error(res.error);
+    created.push(res.data.id);
+    expect(res.data.key).toBe("test_kategorie_zz");
+    expect(res.data.color).toBe("#123456");
+    expect(res.data.is_active).toBe(true);
+    expect(await isCategoryKeyActive("test_kategorie_zz")).toBe(true);
+  });
+
+  it("dedupes a colliding slug", async () => {
+    const res = await createPlanCategory({
+      label: "Test Kategorie ZZ",
+      color: "#222222",
+    });
+    if ("error" in res) throw new Error(res.error);
+    created.push(res.data.id);
+    expect(res.data.key).toBe("test_kategorie_zz_2");
+  });
+
+  it("updates label and color (key immutable)", async () => {
+    const res = await createPlanCategory({
+      label: "Test Upd ZZ",
+      color: "#aaaaaa",
+    });
+    if ("error" in res) throw new Error(res.error);
+    created.push(res.data.id);
+    const upd = await updatePlanCategory(res.data.id, {
+      label: "Test Upd2 ZZ",
+      color: "#bbbbbb",
+    });
+    if ("error" in upd) throw new Error(upd.error);
+    expect(upd.data.label).toBe("Test Upd2 ZZ");
+    expect(upd.data.color).toBe("#bbbbbb");
+    expect(upd.data.key).toBe("test_upd_zz");
+  });
+
+  it("deactivate hides the key from active check", async () => {
+    const res = await createPlanCategory({
+      label: "Test Deact ZZ",
+      color: "#cccccc",
+    });
+    if ("error" in res) throw new Error(res.error);
+    created.push(res.data.id);
+    await deactivatePlanCategory(res.data.id);
+    expect(await isCategoryKeyActive("test_deact_zz")).toBe(false);
+  });
+});
diff --git a/src/services/planCategory.service.ts b/src/services/planCategory.service.ts
new file mode 100644
index 0000000..193ac7b
--- /dev/null
+++ b/src/services/planCategory.service.ts
@@ -0,0 +1,121 @@
+import prisma from "../config/database";
+
+export type CatResult<T> = { data: T } | { error: string; status: number };
+
+/** ASCII slug: strip diacritics, lowercase, non-alphanumerics → underscore. */
+export function slugifyCategory(label: string): string {
+  return label
+    .normalize("NFD")
+    .replace(/[̀-ͯ]/g, "")
+    .toLowerCase()
+    .replace(/[^a-z0-9]+/g, "_")
+    .replace(/^_+|_+$/g, "");
+}
+
+export async function listPlanCategories(includeInactive = true) {
+  return prisma.plan_categories.findMany({
+    where: includeInactive ? {} : { is_active: true },
+    orderBy: [{ sort_order: "asc" }, { id: "asc" }],
+  });
+}
+
+export async function isCategoryKeyActive(key: string): Promise<boolean> {
+  const cat = await prisma.plan_categories.findFirst({
+    where: { key, is_active: true },
+    select: { id: true },
+  });
+  return cat !== null;
+}
+
+async function uniqueKey(base: string): Promise<string> {
+  const root = base || "kategorie";
+  let candidate = root;
+  let n = 2;
+  while (
+    await prisma.plan_categories.findUnique({
+      where: { key: candidate },
+      select: { id: true },
+    })
+  ) {
+    candidate = `${root}_${n++}`;
+  }
+  return candidate;
+}
+
+export async function createPlanCategory(input: {
+  label: string;
+  color: string;
+}): Promise<
+  CatResult<{
+    id: number;
+    key: string;
+    label: string;
+    color: string;
+    sort_order: number;
+    is_active: boolean;
+  }>
+> {
+  const key = await uniqueKey(slugifyCategory(input.label));
+  const max = await prisma.plan_categories.aggregate({
+    _max: { sort_order: true },
+  });
+  const sort_order = (max._max.sort_order ?? 0) + 1;
+  const data = await prisma.plan_categories.create({
+    data: {
+      key,
+      label: input.label,
+      color: input.color,
+      sort_order,
+      is_active: true,
+    },
+  });
+  return { data };
+}
+
+export async function updatePlanCategory(
+  id: number,
+  input: { label?: string; color?: string; is_active?: boolean },
+): Promise<
+  CatResult<{
+    id: number;
+    key: string;
+    label: string;
+    color: string;
+    sort_order: number;
+    is_active: boolean;
+  }>
+> {
+  const existing = await prisma.plan_categories.findUnique({ where: { id } });
+  if (!existing) return { error: "Kategorie nenalezena", status: 404 };
+
+  // Guard: never deactivate the last active category.
+  if (input.is_active === false && existing.is_active) {
+    const activeCount = await prisma.plan_categories.count({
+      where: { is_active: true },
+    });
+    if (activeCount <= 1) {
+      return {
+        error: "Musí zůstat alespoň jedna aktivní kategorie",
+        status: 400,
+      };
+    }
+  }
+
+  const data = await prisma.plan_categories.update({
+    where: { id },
+    data: {
+      label: input.label ?? undefined,
+      color: input.color ?? undefined,
+      is_active: input.is_active ?? undefined,
+    },
+  });
+  return { data };
+}
+
+export async function deactivatePlanCategory(
+  id: number,
+): Promise<CatResult<{ ok: true }>> {
+  const res = await updatePlanCategory(id, { is_active: false });
+  if ("error" in res) return res;
+  return { data: { ok: true } };
+}