diff --git a/backend/src/mcp/tools/accounting.ts b/backend/src/mcp/tools/accounting.ts
index 2462d47..0d44887 100644
--- a/backend/src/mcp/tools/accounting.ts
+++ b/backend/src/mcp/tools/accounting.ts
@@ -41,6 +41,23 @@ const allowedOutgoingDocumentTypes = new Set([
     "serialInvoices",
 ])
 
+const allowedOutgoingDocumentTaxTypes = new Set([
+    "Standard",
+    "13b UStG",
+    "19 UStG",
+    "12.3 UStG",
+])
+
+const outgoingDocumentTaxableTypes = new Set([
+    "invoices",
+    "cancellationInvoices",
+    "advanceInvoices",
+    "serialInvoices",
+    "confirmationOrders",
+    "quotes",
+    "costEstimates",
+])
+
 const documentTypeArg = (args: Record<string, unknown>, key = "type") => {
     const type = stringArg(args, key) || "invoices"
     if (!allowedOutgoingDocumentTypes.has(type)) {
@@ -49,6 +66,50 @@ const documentTypeArg = (args: Record<string, unknown>, key = "type") => {
     return type
 }
 
+const normalizeOutgoingDocumentTaxType = (value: unknown) => {
+    const taxType = typeof value === "string" && value.trim() ? value.trim() : "Standard"
+    if (!allowedOutgoingDocumentTaxTypes.has(taxType)) {
+        throw new Error(`Ungültiger Dokument-Steuertyp: ${taxType}`)
+    }
+    return taxType
+}
+
+const applyOutgoingDocumentTaxType = (
+    payload: Record<string, unknown>,
+    args: Record<string, unknown>,
+    documentType: string,
+    existingTaxType?: unknown,
+    existingRows?: unknown
+) => {
+    if (!outgoingDocumentTaxableTypes.has(documentType)) {
+        payload.taxType = null
+        return
+    }
+
+    const taxType = args.taxType !== undefined
+        ? normalizeOutgoingDocumentTaxType(args.taxType)
+        : existingTaxType
+            ? normalizeOutgoingDocumentTaxType(existingTaxType)
+            : "Standard"
+
+    payload.taxType = taxType
+
+    if (["13b UStG", "19 UStG", "12.3 UStG"].includes(taxType)) {
+        const rows = Array.isArray(payload.rows)
+            ? payload.rows
+            : Array.isArray(existingRows)
+                ? existingRows
+                : null
+
+        if (!rows) return
+
+        payload.rows = rows.map((row: any) => ({
+            ...row,
+            taxPercent: 0,
+        }))
+    }
+}
+
 const optionalObjectArg = (args: Record<string, unknown>, key: string) => {
     const value = args[key]
     return value && typeof value === "object" && !Array.isArray(value) ? value : null
@@ -91,7 +152,6 @@ const buildOutgoingDocumentPayload = (
         "description",
         "startText",
         "endText",
-        "taxType",
     ]
 
     for (const field of stringFields) {
@@ -210,6 +270,26 @@ const validateIncomingInvoiceData = (invoice: Record<string, any>) => {
 }
 
 export const accountingTools: McpTool[] = [
+    {
+        name: "accounting.outgoing_documents.tax_types.list",
+        title: "Steuertypen für Ausgangsbelege auflisten",
+        description: "Listet die unterstützten Dokument-Steuertypen für Ausgangsbelege.",
+        requiredPermissions: ["accounting.outgoing_documents.read"],
+        inputSchema: {
+            type: "object",
+            properties: {},
+        },
+        async handler() {
+            return {
+                rows: [
+                    { key: "Standard", label: "Standard", forcesZeroTaxPercent: false },
+                    { key: "13b UStG", label: "13b UStG", forcesZeroTaxPercent: true },
+                    { key: "19 UStG", label: "19 UStG Kleinunternehmer", forcesZeroTaxPercent: true },
+                    { key: "12.3 UStG", label: "12.3 UStG", forcesZeroTaxPercent: true },
+                ],
+            }
+        },
+    },
     {
         name: "accounting.outgoing_documents.list",
         title: "Ausgangsbelege auflisten",
@@ -299,7 +379,11 @@ export const accountingTools: McpTool[] = [
                 deliveryDateType: { type: "string" },
                 paymentDays: { type: "number" },
                 payment_type: { type: "string" },
-                taxType: { type: "string" },
+                taxType: {
+                    type: "string",
+                    enum: ["Standard", "13b UStG", "19 UStG", "12.3 UStG"],
+                    description: "Steuertyp des gesamten Ausgangsdokuments, nicht der einzelne USt-Satz einer Position.",
+                },
                 title: { type: "string" },
                 description: { type: "string" },
                 startText: { type: "string" },
@@ -316,6 +400,7 @@ export const accountingTools: McpTool[] = [
             assertNoManualDocumentNumber(args)
             const payload = buildOutgoingDocumentPayload(args, context.userId, context.tenantId, true)
             payload.state = "Entwurf"
+            applyOutgoingDocumentTaxType(payload, args, String(payload.type))
 
             const [created] = await context.server.db
                 .insert(createddocuments)
@@ -348,7 +433,11 @@ export const accountingTools: McpTool[] = [
                 deliveryDateType: { type: "string" },
                 paymentDays: { type: "number" },
                 payment_type: { type: "string" },
-                taxType: { type: "string" },
+                taxType: {
+                    type: "string",
+                    enum: ["Standard", "13b UStG", "19 UStG", "12.3 UStG"],
+                    description: "Steuertyp des gesamten Ausgangsdokuments, nicht der einzelne USt-Satz einer Position.",
+                },
                 title: { type: "string" },
                 description: { type: "string" },
                 startText: { type: "string" },
@@ -377,6 +466,7 @@ export const accountingTools: McpTool[] = [
 
             const payload = buildOutgoingDocumentPayload(args, context.userId, context.tenantId)
             payload.state = "Entwurf"
+            applyOutgoingDocumentTaxType(payload, args, String(payload.type || existing.type), existing.taxType, existing.rows)
 
             const [updated] = await context.server.db
                 .update(createddocuments)
@@ -402,7 +492,11 @@ export const accountingTools: McpTool[] = [
                 deliveryDateEnd: { type: "string" },
                 paymentDays: { type: "number" },
                 payment_type: { type: "string" },
-                taxType: { type: "string" },
+                taxType: {
+                    type: "string",
+                    enum: ["Standard", "13b UStG", "19 UStG", "12.3 UStG"],
+                    description: "Steuertyp des gesamten Ausgangsdokuments, nicht der einzelne USt-Satz einer Position.",
+                },
                 rows: { type: "array" },
                 report: { type: "object" },
                 availableInPortal: { type: "boolean" },
@@ -427,6 +521,7 @@ export const accountingTools: McpTool[] = [
 
             payload.state = "Gebucht"
             payload.documentNumber = result.usedNumber
+            applyOutgoingDocumentTaxType(payload, args, existing.type, existing.taxType, existing.rows)
 
             const [updated] = await context.server.db
                 .update(createddocuments)