diff --git a/mcp/src/server.ts b/mcp/src/server.ts
index 3007639..e88cab7 100644
--- a/mcp/src/server.ts
+++ b/mcp/src/server.ts
@@ -15,6 +15,25 @@ import { getHistory } from "./tools/get-history.js";
 
 type Lang = "en" | "ko";
 
+// Common output schema for all tools (markdown text content)
+const TEXT_OUTPUT = {
+  type: "object" as const,
+  properties: {
+    content: {
+      type: "array",
+      items: {
+        type: "object",
+        properties: {
+          type: { type: "string", const: "text" },
+          text: { type: "string", description: "Markdown-formatted inspection result" },
+        },
+        required: ["type", "text"],
+      },
+    },
+  },
+  required: ["content"],
+};
+
 const STANDARDS = [
   "wcag_2.0_a",
   "wcag_2.0_aa",
@@ -57,6 +76,7 @@ export function createServer(apiUrl: string, defaultLang: Lang): Server {
           idempotentHint: true,
           openWorldHint: true,
         },
+        outputSchema: TEXT_OUTPUT,
         inputSchema: {
           type: "object" as const,
           properties: {
@@ -88,6 +108,7 @@ export function createServer(apiUrl: string, defaultLang: Lang): Server {
           idempotentHint: false,
           openWorldHint: true,
         },
+        outputSchema: TEXT_OUTPUT,
         inputSchema: {
           type: "object" as const,
           properties: {
@@ -127,6 +148,7 @@ export function createServer(apiUrl: string, defaultLang: Lang): Server {
           idempotentHint: true,
           openWorldHint: false,
         },
+        outputSchema: TEXT_OUTPUT,
         inputSchema: {
           type: "object" as const,
           properties: {
@@ -153,6 +175,7 @@ export function createServer(apiUrl: string, defaultLang: Lang): Server {
           idempotentHint: true,
           openWorldHint: false,
         },
+        outputSchema: TEXT_OUTPUT,
         inputSchema: {
           type: "object" as const,
           properties: {
@@ -198,6 +221,7 @@ export function createServer(apiUrl: string, defaultLang: Lang): Server {
           idempotentHint: true,
           openWorldHint: false,
         },
+        outputSchema: TEXT_OUTPUT,
         inputSchema: {
           type: "object" as const,
           properties: {