diff --git a/mcp-gateway/wave-mcp/src/types.ts b/mcp-gateway/wave-mcp/src/types.ts
new file mode 100644
index 0000000..6df8307
--- /dev/null
+++ b/mcp-gateway/wave-mcp/src/types.ts
@@ -0,0 +1,161 @@
+// ── Config ────────────────────────────────────────────────────────────────────
+
+export interface WaveConfig {
+  accessToken: string;
+}
+
+// ── Pagination ────────────────────────────────────────────────────────────────
+
+export interface PageInfo {
+  currentPage: number;
+  totalPages: number;
+  totalCount: number;
+}
+
+export interface PaginatedResult<T = unknown> {
+  total: number;
+  count: number;
+  page: number;
+  totalPages: number;
+  items: T[];
+  has_more: boolean;
+  next_page?: number;
+}
+
+// ── GraphQL ───────────────────────────────────────────────────────────────────
+
+export interface GraphQLResponse<T = unknown> {
+  data?: T;
+  errors?: Array<{ message: string; locations?: unknown; path?: unknown }>;
+}
+
+export interface MutationResult {
+  didSucceed: boolean;
+  inputErrors: Array<{
+    code: string;
+    message: string;
+    path?: string[];
+  }>;
+}
+
+// ── Index-signature base (required for structuredContent) ────────────────────
+
+export type JsonObject = { [key: string]: unknown };
+
+// ── Wave Entities ─────────────────────────────────────────────────────────────
+
+export interface WaveBusiness extends JsonObject {
+  id: string;
+  name: string;
+  isPersonal: boolean;
+  organizationalType?: string;
+  isClassicAccounting: boolean;
+  isClassicInvoicing: boolean;
+  currency: { code: string; symbol: string; name: string };
+  address?: {
+    addressLine1?: string;
+    addressLine2?: string;
+    city?: string;
+    province?: { name: string; code: string };
+    country?: { name: string; code: string };
+    postalCode?: string;
+  };
+}
+
+export interface WaveCustomer extends JsonObject {
+  id: string;
+  name: string;
+  firstName?: string;
+  lastName?: string;
+  email?: string;
+  currency?: { code: string };
+  address?: {
+    addressLine1?: string;
+    city?: string;
+    country?: { name: string; code: string };
+    postalCode?: string;
+  };
+  createdAt: string;
+  modifiedAt: string;
+}
+
+export interface WaveProduct extends JsonObject {
+  id: string;
+  name: string;
+  description?: string;
+  unitPrice?: number;
+  isSold: boolean;
+  isBought: boolean;
+  isArchived: boolean;
+  incomeAccount?: { id: string; name: string };
+  expenseAccount?: { id: string; name: string };
+  currency?: { code: string };
+  createdAt: string;
+  modifiedAt: string;
+}
+
+export interface WaveInvoiceItem extends JsonObject {
+  product?: { id: string; name: string };
+  description?: string;
+  quantity: number;
+  unitPrice: number;
+  subtotal: number;
+  total: number;
+  account?: { id: string; name: string };
+  taxes?: Array<{ amount: { value: number }; salesTaxRate?: { name: string } }>;
+}
+
+export interface WaveInvoice extends JsonObject {
+  id: string;
+  pdfUrl?: string;
+  viewUrl?: string;
+  status: string;
+  title?: string;
+  subhead?: string;
+  invoiceNumber: string;
+  invoiceDate?: string;
+  dueDate?: string;
+  memo?: string;
+  customer: WaveCustomer;
+  currency: { code: string };
+  amountDue: { value: number; currency: { code: string } };
+  amountPaid: { value: number; currency: { code: string } };
+  taxTotal: { value: number; currency: { code: string } };
+  subtotal: { value: number; currency: { code: string } };
+  total: { value: number; currency: { code: string } };
+  items: WaveInvoiceItem[];
+  createdAt: string;
+  modifiedAt: string;
+}
+
+export interface WaveAccount extends JsonObject {
+  id: string;
+  name: string;
+  description?: string;
+  displayId: string;
+  type: { name: string; value: string; normalBalanceType: string };
+  subtype: { name: string; value: string };
+  currency: { code: string };
+  isArchived: boolean;
+  sequence: number;
+  normalBalanceType: string;
+}
+
+export interface WaveTransaction extends JsonObject {
+  id: string;
+  description?: string;
+  notes?: string;
+  anchor: {
+    account: { id: string; name: string };
+    amount: { value: number; currency: { code: string } };
+    direction: string;
+  };
+  lineItems: Array<{
+    account: { id: string; name: string };
+    amount: { value: number; currency: { code: string } };
+    description?: string;
+    balance?: string;
+  }>;
+  createdAt: string;
+  modifiedAt: string;
+}