diff --git a/mcp-gateway/wave-mcp/src/tools/invoices.ts b/mcp-gateway/wave-mcp/src/tools/invoices.ts
new file mode 100644
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+++ b/mcp-gateway/wave-mcp/src/tools/invoices.ts
@@ -0,0 +1,458 @@
+import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
+import { z } from "zod";
+import { WaveClient } from "../services/wave-client.js";
+import { WaveInvoice } from "../types.js";
+import { DEFAULT_PAGE_SIZE, MAX_PAGE_SIZE } from "../constants.js";
+
+interface InvoicesData {
+  business: {
+    invoices: {
+      pageInfo: { currentPage: number; totalPages: number; totalCount: number };
+      edges: Array<{ node: WaveInvoice }>;
+    };
+  };
+}
+
+interface InvoiceData {
+  business: { invoice: WaveInvoice };
+}
+
+interface InvoiceCreateData {
+  invoiceCreate: {
+    didSucceed: boolean;
+    inputErrors: Array<{ code: string; message: string; path: string[] }>;
+    invoice?: WaveInvoice;
+  };
+}
+
+interface InvoicePatchData {
+  invoicePatch: {
+    didSucceed: boolean;
+    inputErrors: Array<{ code: string; message: string; path: string[] }>;
+    invoice?: WaveInvoice;
+  };
+}
+
+interface InvoiceActionData {
+  invoiceApprove?: { didSucceed: boolean; inputErrors: Array<{ message: string }> };
+  invoiceSend?: { didSucceed: boolean; inputErrors: Array<{ message: string }>; invoice?: { id: string } };
+  invoiceMarkSent?: { didSucceed: boolean; inputErrors: Array<{ message: string }> };
+  invoiceDelete?: { didSucceed: boolean; inputErrors: Array<{ message: string }> };
+}
+
+const INVOICE_FIELDS = `
+  id pdfUrl viewUrl status title subhead invoiceNumber
+  invoiceDate dueDate memo
+  customer { id name email }
+  currency { code }
+  amountDue { value currency { code } }
+  amountPaid { value currency { code } }
+  taxTotal { value currency { code } }
+  subtotal { value currency { code } }
+  total { value currency { code } }
+  items {
+    product { id name }
+    description quantity unitPrice subtotal total
+    account { id name }
+  }
+  createdAt modifiedAt
+`;
+
+function formatInvoiceMarkdown(inv: WaveInvoice): string[] {
+  const lines = [
+    `## Invoice #${inv.invoiceNumber} — ${inv.customer?.name ?? "Unknown"} (${inv.id})`,
+    `- **Status**: ${inv.status}`,
+    `- **Date**: ${inv.invoiceDate ?? "N/A"}`,
+    `- **Due**: ${inv.dueDate ?? "N/A"}`,
+    `- **Total**: ${WaveClient.formatCurrency(inv.total?.value ?? 0, inv.currency?.code ?? "")}`,
+    `- **Amount Due**: ${WaveClient.formatCurrency(inv.amountDue?.value ?? 0, inv.currency?.code ?? "")}`,
+    `- **Amount Paid**: ${WaveClient.formatCurrency(inv.amountPaid?.value ?? 0, inv.currency?.code ?? "")}`,
+  ];
+  if (inv.pdfUrl) lines.push(`- **PDF**: ${inv.pdfUrl}`);
+  if (inv.viewUrl) lines.push(`- **View**: ${inv.viewUrl}`);
+  lines.push("");
+  return lines;
+}
+
+export function registerInvoiceTools(server: McpServer, client: WaveClient): void {
+  // ── wave_list_invoices ────────────────────────────────────────────────────
+
+  server.registerTool(
+    "wave_list_invoices",
+    {
+      title: "List Wave Invoices",
+      description: `List invoices for a Wave business with optional filtering by status or customer.
+
+Args:
+  - businessId (string): Wave business ID
+  - page (number): Page number (default: 1)
+  - pageSize (number): Items per page, 1-100 (default: 20)
+  - customerId (string): Filter by customer ID (optional)
+  - invoiceNumber (string): Filter by invoice number (optional)
+  - status ('DRAFT' | 'APPROVED' | 'SENT' | 'VIEWED' | 'PARTIALLY_PAID' | 'PAID' | 'OVERDUE'): Filter by status (optional)
+  - response_format ('markdown' | 'json'): Output format (default: 'markdown')
+
+Returns:
+  Paginated list of invoices with totals, status, and customer info.`,
+      inputSchema: z.object({
+        businessId: z.string().describe("Wave business ID"),
+        page: z.number().int().min(1).default(1).describe("Page number"),
+        pageSize: z.number().int().min(1).max(MAX_PAGE_SIZE).default(DEFAULT_PAGE_SIZE).describe("Items per page"),
+        customerId: z.string().optional().describe("Filter by customer ID"),
+        invoiceNumber: z.string().optional().describe("Filter by invoice number"),
+        status: z.enum(["DRAFT", "APPROVED", "SENT", "VIEWED", "PARTIALLY_PAID", "PAID", "OVERDUE"]).optional().describe("Filter by status"),
+        response_format: z.enum(["markdown", "json"]).default("markdown").describe("Output format"),
+      }),
+      annotations: { readOnlyHint: true, destructiveHint: false, idempotentHint: true, openWorldHint: true },
+    },
+    async ({ businessId, page, pageSize, customerId, invoiceNumber, status, response_format }) => {
+      try {
+        // Build optional filter variables
+        const vars: Record<string, unknown> = { businessId, page, pageSize };
+        if (customerId) vars.customerId = customerId;
+        if (invoiceNumber) vars.invoiceNumber = invoiceNumber;
+        if (status) vars.status = status;
+
+        const data = await client.query<InvoicesData>(`
+          query($businessId: ID!, $page: Int!, $pageSize: Int!) {
+            business(id: $businessId) {
+              invoices(page: $page, pageSize: $pageSize) {
+                pageInfo { currentPage totalPages totalCount }
+                edges { node { ${INVOICE_FIELDS} } }
+              }
+            }
+          }
+        `, vars);
+
+        let { pageInfo, edges } = data.business.invoices;
+        let invoices = edges.map((e) => e.node);
+
+        // Client-side filter since Wave API may not support all filter params at query level
+        if (customerId) invoices = invoices.filter((i) => i.customer?.id === customerId);
+        if (status) invoices = invoices.filter((i) => i.status === status);
+        if (invoiceNumber) invoices = invoices.filter((i) => i.invoiceNumber?.includes(invoiceNumber));
+
+        if (!invoices.length) {
+          return { content: [{ type: "text", text: "No invoices found matching the criteria." }] };
+        }
+
+        const result = {
+          total: pageInfo.totalCount,
+          count: invoices.length,
+          page: pageInfo.currentPage,
+          totalPages: pageInfo.totalPages,
+          has_more: pageInfo.currentPage < pageInfo.totalPages,
+          next_page: pageInfo.currentPage < pageInfo.totalPages ? pageInfo.currentPage + 1 : undefined,
+          invoices,
+        };
+
+        let text: string;
+        if (response_format === "json") {
+          text = JSON.stringify(result, null, 2);
+        } else {
+          const lines = [`# Invoices (${pageInfo.totalCount} total, page ${pageInfo.currentPage}/${pageInfo.totalPages})`, ""];
+          for (const inv of invoices) lines.push(...formatInvoiceMarkdown(inv));
+          text = lines.join("\n");
+        }
+
+        return {
+          content: [{ type: "text", text: WaveClient.truncate(text) }],
+          structuredContent: result,
+        };
+      } catch (error) {
+        return { content: [{ type: "text", text: `Error: ${error instanceof Error ? error.message : String(error)}` }] };
+      }
+    }
+  );
+
+  // ── wave_get_invoice ──────────────────────────────────────────────────────
+
+  server.registerTool(
+    "wave_get_invoice",
+    {
+      title: "Get Wave Invoice",
+      description: `Get full details for a specific invoice including line items.
+
+Args:
+  - businessId (string): Wave business ID
+  - invoiceId (string): Invoice ID
+  - response_format ('markdown' | 'json'): Output format (default: 'markdown')
+
+Returns:
+  Full invoice with all line items, totals, dates, and PDF/view links.`,
+      inputSchema: z.object({
+        businessId: z.string().describe("Wave business ID"),
+        invoiceId: z.string().describe("Invoice ID"),
+        response_format: z.enum(["markdown", "json"]).default("markdown").describe("Output format"),
+      }),
+      annotations: { readOnlyHint: true, destructiveHint: false, idempotentHint: true, openWorldHint: true },
+    },
+    async ({ businessId, invoiceId, response_format }) => {
+      try {
+        const data = await client.query<InvoiceData>(`
+          query($businessId: ID!, $invoiceId: ID!) {
+            business(id: $businessId) {
+              invoice(id: $invoiceId) { ${INVOICE_FIELDS} }
+            }
+          }
+        `, { businessId, invoiceId });
+
+        const inv = data.business.invoice;
+        if (!inv) return { content: [{ type: "text", text: `No invoice found with ID: ${invoiceId}` }] };
+
+        let text: string;
+        if (response_format === "json") {
+          text = JSON.stringify(inv, null, 2);
+        } else {
+          const lines = [...formatInvoiceMarkdown(inv)];
+          if (inv.items?.length) {
+            lines.push("### Line Items", "");
+            for (const item of inv.items) {
+              const desc = item.description ?? item.product?.name ?? "Item";
+              lines.push(`- ${desc}: ${item.quantity} × ${WaveClient.formatCurrency(item.unitPrice, inv.currency?.code ?? "")} = ${WaveClient.formatCurrency(item.total, inv.currency?.code ?? "")}`);
+            }
+          }
+          text = lines.join("\n");
+        }
+
+        return { content: [{ type: "text", text }], structuredContent: inv };
+      } catch (error) {
+        return { content: [{ type: "text", text: `Error: ${error instanceof Error ? error.message : String(error)}` }] };
+      }
+    }
+  );
+
+  // ── wave_create_invoice ───────────────────────────────────────────────────
+
+  server.registerTool(
+    "wave_create_invoice",
+    {
+      title: "Create Wave Invoice",
+      description: `Create a new draft invoice in Wave.
+
+Args:
+  - businessId (string): Wave business ID
+  - customerId (string): Customer ID for the invoice
+  - invoiceDate (string): Invoice date in YYYY-MM-DD format (optional, defaults to today)
+  - dueDate (string): Due date in YYYY-MM-DD format (optional)
+  - invoiceNumber (string): Custom invoice number (optional, auto-assigned if omitted)
+  - memo (string): Note to appear on invoice (optional)
+  - items (array): Line items (required, at least 1)
+    - productId (string): Product ID (optional)
+    - description (string): Item description
+    - quantity (number): Quantity
+    - unitPrice (number): Unit price
+    - accountId (string): Revenue account ID (optional)
+  - response_format ('markdown' | 'json'): Output format (default: 'markdown')
+
+Returns:
+  Created invoice details or validation errors.`,
+      inputSchema: z.object({
+        businessId: z.string().describe("Wave business ID"),
+        customerId: z.string().describe("Customer ID"),
+        invoiceDate: z.string().regex(/^\d{4}-\d{2}-\d{2}$/).optional().describe("Invoice date (YYYY-MM-DD)"),
+        dueDate: z.string().regex(/^\d{4}-\d{2}-\d{2}$/).optional().describe("Due date (YYYY-MM-DD)"),
+        invoiceNumber: z.string().optional().describe("Custom invoice number"),
+        memo: z.string().optional().describe("Memo/note on invoice"),
+        items: z.array(z.object({
+          productId: z.string().optional().describe("Product ID"),
+          description: z.string().optional().describe("Line item description"),
+          quantity: z.number().min(0.001).describe("Quantity"),
+          unitPrice: z.number().describe("Unit price"),
+          accountId: z.string().optional().describe("Revenue account ID"),
+        })).min(1).describe("Line items (at least 1 required)"),
+        response_format: z.enum(["markdown", "json"]).default("markdown").describe("Output format"),
+      }),
+      annotations: { readOnlyHint: false, destructiveHint: false, idempotentHint: false, openWorldHint: true },
+    },
+    async ({ businessId, customerId, invoiceDate, dueDate, invoiceNumber, memo, items, response_format }) => {
+      try {
+        const input: Record<string, unknown> = {
+          businessId,
+          customerId,
+          items: items.map((item) => {
+            const li: Record<string, unknown> = {
+              quantity: item.quantity,
+              unitPrice: item.unitPrice,
+            };
+            if (item.productId) li.productId = item.productId;
+            if (item.description) li.description = item.description;
+            if (item.accountId) li.accountId = item.accountId;
+            return li;
+          }),
+        };
+        if (invoiceDate) input.invoiceDate = invoiceDate;
+        if (dueDate) input.dueDate = dueDate;
+        if (invoiceNumber) input.invoiceNumber = invoiceNumber;
+        if (memo) input.memo = memo;
+
+        const data = await client.query<InvoiceCreateData>(`
+          mutation($input: InvoiceCreateInput!) {
+            invoiceCreate(input: $input) {
+              didSucceed
+              inputErrors { code message path }
+              invoice { ${INVOICE_FIELDS} }
+            }
+          }
+        `, { input });
+
+        const result = data.invoiceCreate;
+        if (!result.didSucceed) {
+          const errs = result.inputErrors.map((e) => `  - ${e.path?.join(".") ?? "field"}: ${e.message}`).join("\n");
+          return { content: [{ type: "text", text: `Failed to create invoice:\n${errs}` }] };
+        }
+
+        let text: string;
+        if (response_format === "json") {
+          text = JSON.stringify(result.invoice, null, 2);
+        } else {
+          text = `Invoice created successfully!\n\n${formatInvoiceMarkdown(result.invoice!).join("\n")}`;
+        }
+
+        return { content: [{ type: "text", text }], structuredContent: result.invoice };
+      } catch (error) {
+        return { content: [{ type: "text", text: `Error: ${error instanceof Error ? error.message : String(error)}` }] };
+      }
+    }
+  );
+
+  // ── wave_approve_invoice ──────────────────────────────────────────────────
+
+  server.registerTool(
+    "wave_approve_invoice",
+    {
+      title: "Approve Wave Invoice",
+      description: `Approve a draft invoice, moving it to APPROVED status so it can be sent.
+
+Args:
+  - invoiceId (string): Invoice ID to approve
+
+Returns:
+  Success confirmation or error details.`,
+      inputSchema: z.object({
+        invoiceId: z.string().describe("Invoice ID to approve"),
+      }),
+      annotations: { readOnlyHint: false, destructiveHint: false, idempotentHint: true, openWorldHint: true },
+    },
+    async ({ invoiceId }) => {
+      try {
+        const data = await client.query<InvoiceActionData>(`
+          mutation($input: InvoiceApproveInput!) {
+            invoiceApprove(input: $input) {
+              didSucceed
+              inputErrors { message }
+            }
+          }
+        `, { input: { invoiceId } });
+
+        const result = data.invoiceApprove!;
+        if (!result.didSucceed) {
+          const errs = result.inputErrors.map((e) => `  - ${e.message}`).join("\n");
+          return { content: [{ type: "text", text: `Failed to approve invoice:\n${errs}` }] };
+        }
+
+        return { content: [{ type: "text", text: `Invoice ${invoiceId} approved successfully.` }] };
+      } catch (error) {
+        return { content: [{ type: "text", text: `Error: ${error instanceof Error ? error.message : String(error)}` }] };
+      }
+    }
+  );
+
+  // ── wave_send_invoice ─────────────────────────────────────────────────────
+
+  server.registerTool(
+    "wave_send_invoice",
+    {
+      title: "Send Wave Invoice",
+      description: `Send an approved invoice to the customer via email.
+
+Args:
+  - invoiceId (string): Invoice ID to send
+  - to (array of strings): Recipient email addresses
+  - subject (string): Email subject (optional)
+  - message (string): Email message body (optional)
+
+Returns:
+  Success confirmation or error details.`,
+      inputSchema: z.object({
+        invoiceId: z.string().describe("Invoice ID to send"),
+        to: z.array(z.string().email()).min(1).describe("Recipient email addresses"),
+        subject: z.string().optional().describe("Email subject line"),
+        message: z.string().optional().describe("Email message body"),
+      }),
+      annotations: { readOnlyHint: false, destructiveHint: false, idempotentHint: false, openWorldHint: true },
+    },
+    async ({ invoiceId, to, subject, message }) => {
+      try {
+        const input: Record<string, unknown> = { invoiceId, to };
+        if (subject) input.subject = subject;
+        if (message) input.message = message;
+
+        const data = await client.query<InvoiceActionData>(`
+          mutation($input: InvoiceSendInput!) {
+            invoiceSend(input: $input) {
+              didSucceed
+              inputErrors { message }
+            }
+          }
+        `, { input });
+
+        const result = data.invoiceSend!;
+        if (!result.didSucceed) {
+          const errs = result.inputErrors.map((e) => `  - ${e.message}`).join("\n");
+          return { content: [{ type: "text", text: `Failed to send invoice:\n${errs}` }] };
+        }
+
+        return { content: [{ type: "text", text: `Invoice ${invoiceId} sent to ${to.join(", ")}.` }] };
+      } catch (error) {
+        return { content: [{ type: "text", text: `Error: ${error instanceof Error ? error.message : String(error)}` }] };
+      }
+    }
+  );
+
+  // ── wave_delete_invoice ───────────────────────────────────────────────────
+
+  server.registerTool(
+    "wave_delete_invoice",
+    {
+      title: "Delete Wave Invoice",
+      description: `Delete an invoice. Only DRAFT invoices can be deleted; paid invoices cannot be deleted.
+
+⚠️ This action is irreversible.
+
+Args:
+  - businessId (string): Wave business ID
+  - invoiceId (string): Invoice ID to delete
+
+Returns:
+  Success confirmation or error details.`,
+      inputSchema: z.object({
+        businessId: z.string().describe("Wave business ID"),
+        invoiceId: z.string().describe("Invoice ID to delete"),
+      }),
+      annotations: { readOnlyHint: false, destructiveHint: true, idempotentHint: false, openWorldHint: true },
+    },
+    async ({ businessId, invoiceId }) => {
+      try {
+        const data = await client.query<InvoiceActionData>(`
+          mutation($input: InvoiceDeleteInput!) {
+            invoiceDelete(input: $input) {
+              didSucceed
+              inputErrors { message }
+            }
+          }
+        `, { input: { businessId, invoiceId } });
+
+        const result = data.invoiceDelete!;
+        if (!result.didSucceed) {
+          const errs = result.inputErrors.map((e) => `  - ${e.message}`).join("\n");
+          return { content: [{ type: "text", text: `Failed to delete invoice:\n${errs}` }] };
+        }
+
+        return { content: [{ type: "text", text: `Invoice ${invoiceId} deleted successfully.` }] };
+      } catch (error) {
+        return { content: [{ type: "text", text: `Error: ${error instanceof Error ? error.message : String(error)}` }] };
+      }
+    }
+  );
+}