diff --git a/apps/hq/src/api.ts b/apps/hq/src/api.ts
index aa149e0..0204439 100644
--- a/apps/hq/src/api.ts
+++ b/apps/hq/src/api.ts
@@ -1,10 +1,14 @@
 import { Router, type Response } from 'express'
-import { login, requireAuth } from './auth'
+import { login, requireAuth, requireOwner } from './auth'
 import type { DB } from './db'
 import {
   createClient, getClient, listClients, updateClient,
   type ClientInput, type ClientPatch,
 } from './repos-clients'
+import {
+  createModule, getModule, listModules, listPrices, setPrice,
+  type ModuleInput, type PriceInput,
+} from './repos-modules'
 
 const staffId = (res: Response): string => (res.locals['staff'] as { id: string }).id
 
@@ -51,5 +55,37 @@ export function apiRouter(db: DB): Router {
     }
   })
 
+  // ---------- modules ----------
+  r.get('/modules', requireAuth, (_req, res) => {
+    res.json({ ok: true, modules: listModules(db) })
+  })
+  r.post('/modules', requireAuth, requireOwner, (req, res) => {
+    try {
+      const mod = createModule(db, staffId(res), req.body as ModuleInput)
+      res.json({ ok: true, module: mod })
+    } catch (err) {
+      res.status(400).json({ ok: false, error: err instanceof Error ? err.message : String(err) })
+    }
+  })
+  r.get('/modules/:id/prices', requireAuth, (req, res) => {
+    const id = String(req.params['id'] ?? '')
+    if (getModule(db, id) === null) {
+      res.status(404).json({ ok: false, error: 'Module not found' }); return
+    }
+    res.json({ ok: true, prices: listPrices(db, id) })
+  })
+  r.post('/modules/:id/prices', requireAuth, requireOwner, (req, res) => {
+    const id = String(req.params['id'] ?? '')
+    if (getModule(db, id) === null) {
+      res.status(404).json({ ok: false, error: 'Module not found' }); return
+    }
+    try {
+      setPrice(db, staffId(res), { ...(req.body as Omit<PriceInput, 'moduleId'>), moduleId: id })
+      res.json({ ok: true, prices: listPrices(db, id) })
+    } catch (err) {
+      res.status(400).json({ ok: false, error: err instanceof Error ? err.message : String(err) })
+    }
+  })
+
   return r
 }
diff --git a/apps/hq/src/repos-modules.ts b/apps/hq/src/repos-modules.ts
new file mode 100644
index 0000000..dbf1455
--- /dev/null
+++ b/apps/hq/src/repos-modules.ts
@@ -0,0 +1,117 @@
+import { uuidv7 } from '@sims/domain'
+import { writeAudit } from './audit'
+import type { DB } from './db'
+
+/** Module catalog + dated price book — plain functions over the handle (D12 portable-repo pattern). */
+
+export type Kind = 'one_time' | 'monthly' | 'yearly' | 'usage'
+
+const ALL_KINDS: Kind[] = ['one_time', 'monthly', 'yearly', 'usage']
+
+export interface Module {
+  id: string; code: string; name: string; sac: string
+  allowedKinds: Kind[]; multiSubscription: boolean; active: boolean
+}
+
+interface ModuleRow {
+  id: string; code: string; name: string; sac: string
+  allowed_kinds: string; multi_subscription: number; active: number
+}
+
+function toModule(r: ModuleRow): Module {
+  return {
+    id: r.id, code: r.code, name: r.name, sac: r.sac,
+    allowedKinds: JSON.parse(r.allowed_kinds) as Kind[],
+    multiSubscription: r.multi_subscription === 1,
+    active: r.active === 1,
+  }
+}
+
+export interface ModuleInput {
+  code: string; name: string; sac?: string
+  allowedKinds?: Kind[]; multiSubscription?: boolean
+}
+
+export function getModule(db: DB, id: string): Module | null {
+  const row = db.prepare(`SELECT * FROM module WHERE id=?`).get(id) as ModuleRow | undefined
+  return row === undefined ? null : toModule(row)
+}
+
+export function listModules(db: DB): Module[] {
+  const rows = db.prepare(`SELECT * FROM module ORDER BY code`).all() as ModuleRow[]
+  return rows.map(toModule)
+}
+
+export function createModule(db: DB, userId: string, input: ModuleInput): Module {
+  const kinds = input.allowedKinds ?? ALL_KINDS
+  for (const k of kinds) {
+    if (!ALL_KINDS.includes(k)) throw new Error(`Unknown kind: ${k}`)
+  }
+  const id = uuidv7()
+  db.prepare(
+    `INSERT INTO module (id, code, name, sac, allowed_kinds, multi_subscription)
+     VALUES (?, ?, ?, ?, ?, ?)`,
+  ).run(
+    id, input.code, input.name, input.sac ?? '998313',
+    JSON.stringify(kinds), input.multiSubscription === true ? 1 : 0,
+  )
+  const mod = getModule(db, id)!
+  writeAudit(db, userId, 'create', 'module', id, undefined, mod)
+  return mod
+}
+
+export interface ModulePrice {
+  id: string; moduleId: string; edition: string; kind: Kind
+  pricePaise: number; effectiveFrom: string
+}
+
+interface PriceRow {
+  id: string; module_id: string; edition: string; kind: string
+  price_paise: number; effective_from: string
+}
+
+function toPrice(r: PriceRow): ModulePrice {
+  return {
+    id: r.id, moduleId: r.module_id, edition: r.edition,
+    kind: r.kind as Kind, pricePaise: r.price_paise, effectiveFrom: r.effective_from,
+  }
+}
+
+export interface PriceInput {
+  moduleId: string; edition?: string; kind: Kind; pricePaise: number; effectiveFrom: string
+}
+
+export function setPrice(db: DB, userId: string, input: PriceInput): void {
+  if (!ALL_KINDS.includes(input.kind)) throw new Error(`Unknown kind: ${input.kind}`)
+  if (!Number.isInteger(input.pricePaise) || input.pricePaise < 0) {
+    throw new Error('pricePaise must be a non-negative integer (paise)')
+  }
+  if (getModule(db, input.moduleId) === null) throw new Error('Module not found')
+  const id = uuidv7()
+  const edition = input.edition ?? 'standard'
+  db.prepare(
+    `INSERT INTO module_price_book (id, module_id, edition, kind, price_paise, effective_from)
+     VALUES (?, ?, ?, ?, ?, ?)`,
+  ).run(id, input.moduleId, edition, input.kind, input.pricePaise, input.effectiveFrom)
+  writeAudit(db, userId, 'create', 'module_price_book', id, undefined, {
+    moduleId: input.moduleId, edition, kind: input.kind,
+    pricePaise: input.pricePaise, effectiveFrom: input.effectiveFrom,
+  })
+}
+
+export function listPrices(db: DB, moduleId: string): ModulePrice[] {
+  const rows = db.prepare(
+    `SELECT * FROM module_price_book WHERE module_id=? ORDER BY edition, kind, effective_from`,
+  ).all(moduleId) as PriceRow[]
+  return rows.map(toPrice)
+}
+
+/** Latest effective_from <= onDate wins — the D5 dated-rows philosophy. */
+export function priceOn(db: DB, moduleId: string, kind: Kind, edition: string, onDate: string): number | null {
+  const row = db.prepare(
+    `SELECT price_paise FROM module_price_book
+     WHERE module_id=? AND kind=? AND edition=? AND effective_from <= ?
+     ORDER BY effective_from DESC LIMIT 1`,
+  ).get(moduleId, kind, edition, onDate) as { price_paise: number } | undefined
+  return row === undefined ? null : row.price_paise
+}
diff --git a/apps/hq/test/modules.test.ts b/apps/hq/test/modules.test.ts
new file mode 100644
index 0000000..fbea21e
--- /dev/null
+++ b/apps/hq/test/modules.test.ts
@@ -0,0 +1,15 @@
+import { describe, it, expect } from 'vitest'
+import { openDb } from '../src/db'
+import { createModule, setPrice, priceOn } from '../src/repos-modules'
+
+describe('module catalog', () => {
+  it('resolves the dated price row', () => {
+    const db = openDb(':memory:')
+    const m = createModule(db, 'u1', { code: 'POS', name: 'POS Billing' })
+    setPrice(db, 'u1', { moduleId: m.id, kind: 'yearly', pricePaise: 1_20_000_00, effectiveFrom: '2026-04-01' })
+    setPrice(db, 'u1', { moduleId: m.id, kind: 'yearly', pricePaise: 1_50_000_00, effectiveFrom: '2026-08-01' })
+    expect(priceOn(db, m.id, 'yearly', 'standard', '2026-07-10')).toBe(1_20_000_00)
+    expect(priceOn(db, m.id, 'yearly', 'standard', '2026-09-01')).toBe(1_50_000_00)
+    expect(priceOn(db, m.id, 'monthly', 'standard', '2026-09-01')).toBeNull()
+  })
+})