diff --git a/src/hooks/useCategoryTaxonomy.ts b/src/hooks/useCategoryTaxonomy.ts
new file mode 100644
index 0000000..c01eadb
--- /dev/null
+++ b/src/hooks/useCategoryTaxonomy.ts
@@ -0,0 +1,32 @@
+import { useMemo } from "react";
+import {
+  getTaxonomyV1,
+  findById,
+  findByPath,
+  getLeaves,
+  getParentById,
+  type Taxonomy,
+  type TaxonomyNode,
+  type TaxonomyLeaf,
+} from "../services/categoryTaxonomyService";
+
+export interface UseCategoryTaxonomyResult {
+  taxonomy: Taxonomy;
+  findById: (id: number) => TaxonomyNode | null;
+  findByPath: (path: string[]) => TaxonomyNode | null;
+  getLeaves: () => TaxonomyLeaf[];
+  getParentById: (id: number) => TaxonomyNode | null;
+}
+
+export function useCategoryTaxonomy(): UseCategoryTaxonomyResult {
+  return useMemo<UseCategoryTaxonomyResult>(
+    () => ({
+      taxonomy: getTaxonomyV1(),
+      findById,
+      findByPath,
+      getLeaves,
+      getParentById,
+    }),
+    [],
+  );
+}
diff --git a/src/services/categoryTaxonomyService.test.ts b/src/services/categoryTaxonomyService.test.ts
new file mode 100644
index 0000000..3c834a6
--- /dev/null
+++ b/src/services/categoryTaxonomyService.test.ts
@@ -0,0 +1,102 @@
+import { describe, it, expect, beforeEach } from "vitest";
+import {
+  getTaxonomyV1,
+  findById,
+  findByPath,
+  getLeaves,
+  getParentById,
+  resetTaxonomyCache,
+} from "./categoryTaxonomyService";
+
+beforeEach(() => {
+  resetTaxonomyCache();
+});
+
+describe("getTaxonomyV1", () => {
+  it("returns version v1 with non-empty roots", () => {
+    const tax = getTaxonomyV1();
+    expect(tax.version).toBe("v1");
+    expect(tax.roots.length).toBeGreaterThan(0);
+  });
+
+  it("caches the taxonomy across calls (same reference)", () => {
+    const a = getTaxonomyV1();
+    const b = getTaxonomyV1();
+    expect(a).toBe(b);
+  });
+});
+
+describe("findById", () => {
+  it("finds a root-level node", () => {
+    const node = findById(1000);
+    expect(node).not.toBeNull();
+    expect(node?.name).toBe("Revenus");
+  });
+
+  it("finds a nested leaf node", () => {
+    const node = findById(1011);
+    expect(node).not.toBeNull();
+    expect(node?.i18n_key).toBe("categoriesSeed.revenus.emploi.paie");
+  });
+
+  it("returns null for an unknown id", () => {
+    expect(findById(99999)).toBeNull();
+  });
+});
+
+describe("findByPath", () => {
+  it("returns null for an empty path", () => {
+    expect(findByPath([])).toBeNull();
+  });
+
+  it("finds a root by single-segment path", () => {
+    const node = findByPath(["Revenus"]);
+    expect(node?.id).toBe(1000);
+  });
+
+  it("finds a nested leaf by multi-segment path", () => {
+    const node = findByPath(["Revenus", "Emploi", "Paie régulière"]);
+    expect(node?.id).toBe(1011);
+  });
+
+  it("returns null when a segment does not match", () => {
+    expect(findByPath(["Revenus", "Emploi", "NoSuchLeaf"])).toBeNull();
+    expect(findByPath(["Unknown"])).toBeNull();
+  });
+});
+
+describe("getLeaves", () => {
+  it("returns only nodes with no children", () => {
+    const leaves = getLeaves();
+    expect(leaves.length).toBeGreaterThan(0);
+    for (const leaf of leaves) {
+      expect(leaf.children.length).toBe(0);
+    }
+  });
+
+  it("includes a known leaf by id", () => {
+    const leaves = getLeaves();
+    expect(leaves.some((l) => l.id === 1011)).toBe(true);
+  });
+});
+
+describe("getParentById", () => {
+  it("returns the direct parent of a leaf", () => {
+    const parent = getParentById(1011);
+    expect(parent?.id).toBe(1010);
+    expect(parent?.name).toBe("Emploi");
+  });
+
+  it("returns the root as parent of a level-2 node", () => {
+    const parent = getParentById(1010);
+    expect(parent?.id).toBe(1000);
+  });
+
+  it("returns null for a root-level node", () => {
+    expect(getParentById(1000)).toBeNull();
+  });
+
+  it("returns null for an unknown id", () => {
+    expect(getParentById(99999)).toBeNull();
+  });
+});
diff --git a/src/services/categoryTaxonomyService.ts b/src/services/categoryTaxonomyService.ts
new file mode 100644
index 0000000..3b9aab5
--- /dev/null
+++ b/src/services/categoryTaxonomyService.ts
@@ -0,0 +1,88 @@
+import taxonomyData from "../data/categoryTaxonomyV1.json";
+
+export type TaxonomyCategoryType = "expense" | "income" | "transfer";
+
+export interface TaxonomyNode {
+  id: number;
+  name: string;
+  i18n_key: string;
+  type: TaxonomyCategoryType;
+  color: string;
+  sort_order: number;
+  children: TaxonomyNode[];
+}
+
+export type TaxonomyLeaf = TaxonomyNode & { children: [] };
+
+export type TaxonomyRoot = TaxonomyNode;
+
+export interface Taxonomy {
+  version: string;
+  description: string;
+  roots: TaxonomyRoot[];
+}
+
+let cached: Taxonomy | null = null;
+
+function loadTaxonomy(): Taxonomy {
+  if (cached !== null) return cached;
+  cached = taxonomyData as Taxonomy;
+  return cached;
+}
+
+export function getTaxonomyV1(): Taxonomy {
+  return loadTaxonomy();
+}
+
+export function findById(id: number): TaxonomyNode | null {
+  const stack: TaxonomyNode[] = [...loadTaxonomy().roots];
+  while (stack.length > 0) {
+    const node = stack.pop() as TaxonomyNode;
+    if (node.id === id) return node;
+    stack.push(...node.children);
+  }
+  return null;
+}
+
+export function findByPath(path: string[]): TaxonomyNode | null {
+  if (path.length === 0) return null;
+  const { roots } = loadTaxonomy();
+  let current: TaxonomyNode | undefined = roots.find((r) => r.name === path[0]);
+  for (let i = 1; i < path.length && current !== undefined; i++) {
+    current = current.children.find((c) => c.name === path[i]);
+  }
+  return current ?? null;
+}
+
+export function getLeaves(): TaxonomyLeaf[] {
+  const leaves: TaxonomyLeaf[] = [];
+  const walk = (node: TaxonomyNode): void => {
+    if (node.children.length === 0) {
+      leaves.push(node as TaxonomyLeaf);
+      return;
+    }
+    for (const child of node.children) walk(child);
+  };
+  for (const root of loadTaxonomy().roots) walk(root);
+  return leaves;
+}
+
+export function getParentById(id: number): TaxonomyNode | null {
+  const visit = (node: TaxonomyNode): TaxonomyNode | null => {
+    for (const child of node.children) {
+      if (child.id === id) return node;
+      const deeper = visit(child);
+      if (deeper !== null) return deeper;
+    }
+    return null;
+  };
+  for (const root of loadTaxonomy().roots) {
+    const result = visit(root);
+    if (result !== null) return result;
+  }
+  return null;
+}
+
+export function resetTaxonomyCache(): void {
+  cached = null;
+}