diff --git a/__tests__/api/ideas.test.ts b/__tests__/api/ideas.test.ts
new file mode 100644
index 0000000..448cc6b
--- /dev/null
+++ b/__tests__/api/ideas.test.ts
@@ -0,0 +1,194 @@
+import { describe, it, expect, vi, beforeEach } from 'vitest'
+
+vi.mock('@/lib/prisma', () => ({
+  prisma: {
+    product: { findFirst: vi.fn() },
+    idea: {
+      findFirst: vi.fn(),
+      findMany: vi.fn(),
+      create: vi.fn(),
+      update: vi.fn(),
+    },
+    ideaLog: { findMany: vi.fn() },
+    $transaction: vi.fn(),
+  },
+}))
+vi.mock('@/lib/api-auth', () => ({
+  authenticateApiRequest: vi.fn(),
+}))
+vi.mock('@/lib/idea-code-server', () => ({
+  nextIdeaCode: vi.fn().mockResolvedValue('IDEA-001'),
+}))
+
+import { prisma } from '@/lib/prisma'
+import { authenticateApiRequest } from '@/lib/api-auth'
+import { GET as getIdeas, POST as postIdea } from '@/app/api/ideas/route'
+import { GET as getIdea, PATCH as patchIdea } from '@/app/api/ideas/[id]/route'
+
+type M = {
+  product: { findFirst: ReturnType<typeof vi.fn> }
+  idea: { findFirst: ReturnType<typeof vi.fn>; findMany: ReturnType<typeof vi.fn>; create: ReturnType<typeof vi.fn>; update: ReturnType<typeof vi.fn> }
+  ideaLog: { findMany: ReturnType<typeof vi.fn> }
+  $transaction: ReturnType<typeof vi.fn>
+}
+const m = prisma as unknown as M
+const mockAuth = authenticateApiRequest as ReturnType<typeof vi.fn>
+
+const NOW = new Date('2026-05-04T19:00:00Z')
+
+const IDEA_ROW = {
+  id: 'idea-1',
+  user_id: 'user-1',
+  code: 'IDEA-001',
+  title: 'Plant-watering reminder',
+  description: null,
+  status: 'DRAFT' as const,
+  product_id: null,
+  product: null,
+  pbi: null,
+  pbi_id: null,
+  archived: false,
+  grill_md: null,
+  plan_md: null,
+  created_at: NOW,
+  updated_at: NOW,
+}
+
+function makeRequest(method: 'GET' | 'POST' | 'PATCH', url: string, body?: unknown): Request {
+  return new Request(`http://localhost${url}`, {
+    method,
+    headers: {
+      Authorization: 'Bearer test-token',
+      'Content-Type': 'application/json',
+    },
+    body: body !== undefined ? JSON.stringify(body) : undefined,
+  })
+}
+
+beforeEach(() => {
+  vi.clearAllMocks()
+  mockAuth.mockResolvedValue({ userId: 'user-1', isDemo: false })
+  m.$transaction.mockImplementation(async (arg: unknown) => {
+    if (typeof arg === 'function') return (arg as (tx: unknown) => unknown)(m)
+    return arg
+  })
+})
+
+describe('GET /api/ideas', () => {
+  it('returns user ideas (DTO shape)', async () => {
+    m.idea.findMany.mockResolvedValueOnce([IDEA_ROW])
+    const res = await getIdeas(makeRequest('GET', '/api/ideas'))
+    expect(res.status).toBe(200)
+    const body = await res.json()
+    expect(body.ideas).toHaveLength(1)
+    expect(body.ideas[0]).toMatchObject({
+      id: 'idea-1',
+      code: 'IDEA-001',
+      status: 'draft',
+      has_grill_md: false,
+    })
+  })
+
+  it('rejects unauthenticated', async () => {
+    mockAuth.mockResolvedValueOnce({ error: 'Unauthorized', status: 401 })
+    const res = await getIdeas(makeRequest('GET', '/api/ideas'))
+    expect(res.status).toBe(401)
+  })
+
+  it('filters by archived=false param', async () => {
+    m.idea.findMany.mockResolvedValueOnce([])
+    await getIdeas(makeRequest('GET', '/api/ideas?archived=false'))
+    expect(m.idea.findMany).toHaveBeenCalledWith(
+      expect.objectContaining({
+        where: expect.objectContaining({ archived: false, user_id: 'user-1' }),
+      }),
+    )
+  })
+})
+
+describe('POST /api/ideas', () => {
+  it('creates idea and returns 201', async () => {
+    m.idea.create.mockResolvedValueOnce(IDEA_ROW)
+    const res = await postIdea(makeRequest('POST', '/api/ideas', { title: 'Plant-watering reminder' }))
+    expect(res.status).toBe(201)
+    const body = await res.json()
+    expect(body.idea).toMatchObject({ id: 'idea-1', code: 'IDEA-001', status: 'draft' })
+  })
+
+  it('rejects demo with 403', async () => {
+    mockAuth.mockResolvedValueOnce({ userId: 'demo-1', isDemo: true })
+    const res = await postIdea(makeRequest('POST', '/api/ideas', { title: 'x' }))
+    expect(res.status).toBe(403)
+  })
+
+  it('rejects empty title with 422', async () => {
+    const res = await postIdea(makeRequest('POST', '/api/ideas', { title: '' }))
+    expect(res.status).toBe(422)
+  })
+
+  it('rejects malformed JSON with 400', async () => {
+    const req = new Request('http://localhost/api/ideas', {
+      method: 'POST',
+      headers: { Authorization: 'Bearer test', 'Content-Type': 'application/json' },
+      body: 'not-json',
+    })
+    const res = await postIdea(req)
+    expect(res.status).toBe(400)
+  })
+
+  it('returns 404 when product_id refers to a foreign product', async () => {
+    m.product.findFirst.mockResolvedValueOnce(null)
+    const res = await postIdea(
+      makeRequest('POST', '/api/ideas', {
+        title: 'x',
+        product_id: 'cmohrysyj0000rd17clnjy4tc',
+      }),
+    )
+    expect(res.status).toBe(404)
+  })
+})
+
+describe('GET /api/ideas/[id]', () => {
+  it('returns idea + logs', async () => {
+    m.idea.findFirst.mockResolvedValueOnce(IDEA_ROW)
+    m.ideaLog.findMany.mockResolvedValueOnce([
+      { id: 'l-1', type: 'NOTE', content: 'x', metadata: null, created_at: NOW },
+    ])
+    const ctx = { params: Promise.resolve({ id: 'idea-1' }) }
+    const res = await getIdea(makeRequest('GET', '/api/ideas/idea-1'), ctx)
+    expect(res.status).toBe(200)
+    const body = await res.json()
+    expect(body.idea).toMatchObject({ id: 'idea-1' })
+    expect(body.logs).toHaveLength(1)
+  })
+
+  it('returns 404 (not 403) for foreign user — anti-enumeration', async () => {
+    m.idea.findFirst.mockResolvedValueOnce(null)
+    const ctx = { params: Promise.resolve({ id: 'idea-1' }) }
+    const res = await getIdea(makeRequest('GET', '/api/ideas/idea-1'), ctx)
+    expect(res.status).toBe(404)
+  })
+})
+
+describe('PATCH /api/ideas/[id]', () => {
+  const ctx = { params: Promise.resolve({ id: 'idea-1' }) }
+
+  it('updates editable idea', async () => {
+    m.idea.findFirst.mockResolvedValueOnce({ id: 'idea-1', status: 'DRAFT' })
+    m.idea.update.mockResolvedValueOnce({ ...IDEA_ROW, title: 'Updated' })
+    const res = await patchIdea(makeRequest('PATCH', '/api/ideas/idea-1', { title: 'Updated' }), ctx)
+    expect(res.status).toBe(200)
+  })
+
+  it('blocks demo with 403', async () => {
+    mockAuth.mockResolvedValueOnce({ userId: 'demo-1', isDemo: true })
+    const res = await patchIdea(makeRequest('PATCH', '/api/ideas/idea-1', { title: 'x' }), ctx)
+    expect(res.status).toBe(403)
+  })
+
+  it('blocks update on PLANNED with 422', async () => {
+    m.idea.findFirst.mockResolvedValueOnce({ id: 'idea-1', status: 'PLANNED' })
+    const res = await patchIdea(makeRequest('PATCH', '/api/ideas/idea-1', { title: 'x' }), ctx)
+    expect(res.status).toBe(422)
+  })
+})
diff --git a/app/api/ideas/[id]/route.ts b/app/api/ideas/[id]/route.ts
new file mode 100644
index 0000000..4c547c3
--- /dev/null
+++ b/app/api/ideas/[id]/route.ts
@@ -0,0 +1,91 @@
+// Per-idea REST endpoints (M12). user_id-strict scope, 404 (niet 403) bij
+// foreign user om enumeratie te vermijden.
+
+import { authenticateApiRequest } from '@/lib/api-auth'
+import { prisma } from '@/lib/prisma'
+import { ideaUpdateSchema } from '@/lib/schemas/idea'
+import { isIdeaEditable } from '@/lib/idea-status'
+import { ideaToDto } from '@/lib/idea-dto'
+
+interface RouteContext {
+  params: Promise<{ id: string }>
+}
+
+export async function GET(request: Request, ctx: RouteContext) {
+  const auth = await authenticateApiRequest(request)
+  if ('error' in auth) {
+    return Response.json({ error: auth.error }, { status: auth.status })
+  }
+
+  const { id } = await ctx.params
+
+  const idea = await prisma.idea.findFirst({
+    where: { id, user_id: auth.userId },
+    include: {
+      product: { select: { id: true, name: true, repo_url: true } },
+      pbi: { select: { id: true, code: true, title: true } },
+    },
+  })
+  if (!idea) {
+    return Response.json({ error: 'Idee niet gevonden' }, { status: 404 })
+  }
+
+  // Recente logs (max 50) — handig voor MCP tools die context willen ophalen.
+  const logs = await prisma.ideaLog.findMany({
+    where: { idea_id: id },
+    orderBy: { created_at: 'desc' },
+    take: 50,
+    select: { id: true, type: true, content: true, metadata: true, created_at: true },
+  })
+
+  return Response.json({ idea: ideaToDto(idea), logs })
+}
+
+export async function PATCH(request: Request, ctx: RouteContext) {
+  const auth = await authenticateApiRequest(request)
+  if ('error' in auth) {
+    return Response.json({ error: auth.error }, { status: auth.status })
+  }
+  if (auth.isDemo) {
+    return Response.json({ error: 'Niet beschikbaar in demo-modus' }, { status: 403 })
+  }
+
+  const { id } = await ctx.params
+
+  let body: unknown
+  try {
+    body = await request.json()
+  } catch {
+    return Response.json({ error: 'Malformed JSON' }, { status: 400 })
+  }
+  const parsed = ideaUpdateSchema.safeParse(body)
+  if (!parsed.success) {
+    return Response.json({ error: parsed.error.flatten() }, { status: 422 })
+  }
+
+  const idea = await prisma.idea.findFirst({
+    where: { id, user_id: auth.userId },
+    select: { id: true, status: true },
+  })
+  if (!idea) {
+    return Response.json({ error: 'Idee niet gevonden' }, { status: 404 })
+  }
+  if (!isIdeaEditable(idea.status)) {
+    return Response.json(
+      { error: `Idee niet bewerkbaar in status ${idea.status}` },
+      { status: 422 },
+    )
+  }
+
+  const updated = await prisma.idea.update({
+    where: { id },
+    data: {
+      ...(parsed.data.title !== undefined ? { title: parsed.data.title } : {}),
+      ...(parsed.data.description !== undefined ? { description: parsed.data.description } : {}),
+      ...(parsed.data.product_id !== undefined ? { product_id: parsed.data.product_id } : {}),
+    },
+    include: { product: { select: { id: true, name: true, repo_url: true } } },
+  })
+
+  return Response.json({ idea: ideaToDto(updated) })
+}
diff --git a/app/api/ideas/route.ts b/app/api/ideas/route.ts
new file mode 100644
index 0000000..84d1ad7
--- /dev/null
+++ b/app/api/ideas/route.ts
@@ -0,0 +1,94 @@
+// REST endpoints voor de Idee-entity (M12).
+// - Strikt user_id-only — geen productAccessFilter.
+// - Auth via session OF API-token (zelfde patroon als /api/todos).
+// - Demo blokkeert POST/PATCH/DELETE (proxy.ts laag + 403 hier als second-line).
+
+import { authenticateApiRequest } from '@/lib/api-auth'
+import { prisma } from '@/lib/prisma'
+import { ideaCreateSchema } from '@/lib/schemas/idea'
+import { ideaStatusFromApi, ideaStatusToApi } from '@/lib/idea-status'
+import { nextIdeaCode } from '@/lib/idea-code-server'
+import { ideaToDto } from '@/lib/idea-dto'
+
+export async function GET(request: Request) {
+  const auth = await authenticateApiRequest(request)
+  if ('error' in auth) {
+    return Response.json({ error: auth.error }, { status: auth.status })
+  }
+
+  const url = new URL(request.url)
+  const archivedParam = url.searchParams.get('archived')
+  const productIdParam = url.searchParams.get('product_id')
+  const statusParam = url.searchParams.get('status')
+
+  const archived =
+    archivedParam === 'true' ? true : archivedParam === 'false' ? false : undefined
+  const status = statusParam ? ideaStatusFromApi(statusParam) ?? undefined : undefined
+
+  const ideas = await prisma.idea.findMany({
+    where: {
+      user_id: auth.userId,
+      ...(archived !== undefined ? { archived } : {}),
+      ...(productIdParam ? { product_id: productIdParam } : {}),
+      ...(status ? { status } : {}),
+    },
+    include: { product: { select: { id: true, name: true, repo_url: true } } },
+    orderBy: { created_at: 'desc' },
+    take: 200,
+  })
+
+  return Response.json({ ideas: ideas.map(ideaToDto) })
+}
+
+export async function POST(request: Request) {
+  const auth = await authenticateApiRequest(request)
+  if ('error' in auth) {
+    return Response.json({ error: auth.error }, { status: auth.status })
+  }
+  if (auth.isDemo) {
+    return Response.json({ error: 'Niet beschikbaar in demo-modus' }, { status: 403 })
+  }
+
+  let body: unknown
+  try {
+    body = await request.json()
+  } catch {
+    return Response.json({ error: 'Malformed JSON' }, { status: 400 })
+  }
+  const parsed = ideaCreateSchema.safeParse(body)
+  if (!parsed.success) {
+    return Response.json({ error: parsed.error.flatten() }, { status: 422 })
+  }
+
+  // Optionele product-binding: alleen toelaten als gebruiker eigenaar/member is.
+  if (parsed.data.product_id) {
+    const product = await prisma.product.findFirst({
+      where: { id: parsed.data.product_id, user_id: auth.userId, archived: false },
+      select: { id: true },
+    })
+    if (!product) {
+      return Response.json({ error: 'Product niet gevonden' }, { status: 404 })
+    }
+  }
+
+  const userId = auth.userId
+  const idea = await prisma.$transaction(async (tx) => {
+    const code = await nextIdeaCode(userId, tx)
+    return tx.idea.create({
+      data: {
+        user_id: userId,
+        product_id: parsed.data.product_id ?? null,
+        code,
+        title: parsed.data.title,
+        description: parsed.data.description ?? null,
+        status: 'DRAFT',
+      },
+      include: { product: { select: { id: true, name: true, repo_url: true } } },
+    })
+  })
+
+  return Response.json(
+    { idea: { ...ideaToDto(idea), status: ideaStatusToApi(idea.status) } },
+    { status: 201 },
+  )
+}
diff --git a/lib/idea-dto.ts b/lib/idea-dto.ts
new file mode 100644
index 0000000..b32d14a
--- /dev/null
+++ b/lib/idea-dto.ts
@@ -0,0 +1,49 @@
+// API-projection voor Idea — converteert Prisma-row naar het externe contract.
+// Belangrijk: status wordt naar lowercase API-string vertaald (zelfde patroon
+// als TaskStatus / StoryStatus / PbiStatus elders in de codebase).
+
+import { ideaStatusToApi } from '@/lib/idea-status'
+
+import type { Idea, IdeaStatus, Product } from '@prisma/client'
+
+type IdeaWithProduct = Idea & {
+  product: Pick<Product, 'id' | 'name' | 'repo_url'> | null
+  pbi?: { id: string; code: string; title: string } | null
+}
+
+export interface IdeaDto {
+  id: string
+  code: string
+  title: string
+  description: string | null
+  status: ReturnType<typeof ideaStatusToApi>
+  product_id: string | null
+  product: { id: string; name: string; repo_url: string | null } | null
+  pbi_id: string | null
+  pbi?: { id: string; code: string; title: string } | null
+  archived: boolean
+  has_grill_md: boolean
+  has_plan_md: boolean
+  created_at: string
+  updated_at: string
+}
+
+export function ideaToDto(idea: IdeaWithProduct & { status: IdeaStatus }): IdeaDto {
+  return {
+    id: idea.id,
+    code: idea.code,
+    title: idea.title,
+    description: idea.description,
+    status: ideaStatusToApi(idea.status),
+    product_id: idea.product_id,
+    product: idea.product,
+    pbi_id: idea.pbi_id,
+    pbi: idea.pbi ?? null,
+    archived: idea.archived,
+    // Geen md-content in lijst-payloads (kan groot zijn) — enkel een vlag.
+    has_grill_md: idea.grill_md !== null,
+    has_plan_md: idea.plan_md !== null,
+    created_at: idea.created_at.toISOString(),
+    updated_at: idea.updated_at.toISOString(),
+  }
+}