handle invalid no arg in tool

Author: huozhi

.mcp.json

@@ -1,8 +1,8 @@
 {
   "mcpServers": {
     "next-devtools": {
-      "command": "npx",
-      "args": ["."]
+      "command": "node",
+      "args": ["./dist/index.js"]
     }
   }
 }

src/index.ts

@@ -14,6 +14,7 @@ import {
   ListResourcesRequestSchema,
   ReadResourceRequestSchema,
 } from "@modelcontextprotocol/sdk/types.js"
+import { ZodError } from "zod"
 import { MCP_TOOLS } from "./mcp-tools/index.js"
 import { MCP_PROMPTS, PROMPT_HANDLERS } from "./mcp-prompts/index.js"
 import {
@@ -61,7 +62,27 @@ async function main() {
     }
 
     try {
-      const result = await tool.execute?.(args as any, {
+      // Validate arguments against the tool's input schema
+      let validatedArgs = args || {}
+      if (tool.inputSchema && typeof (tool.inputSchema as any).parse === "function") {
+        try {
+          validatedArgs = (tool.inputSchema as any).parse(args || {})
+        } catch (error) {
+          // Format Zod validation errors for better user experience
+          if (error instanceof ZodError) {
+            const formattedErrors = (error as any).issues
+              .map((err: any) => {
+                const path = err.path.length > 0 ? `${err.path.join(".")}` : "arguments"
+                return `${path}: ${err.message}`
+              })
+              .join("; ")
+            throw new Error(`Invalid arguments - ${formattedErrors}`)
+          }
+          throw error
+        }
+      }
+
+      const result = await tool.execute?.(validatedArgs as any, {
         abortSignal: new AbortController().signal,
         messages: [],
         toolCallId: String(request.params._meta?.progressToken || Date.now()),

src/mcp-tools/nextjs-docs.ts

@@ -8,7 +8,10 @@ import {
 
 // Next.js Docs Tool
 const nextjsDocsInputSchema = z.object({
-  query: z.string().describe("Search query to find relevant Next.js documentation sections"),
+  query: z
+    .string()
+    .min(1, "Query parameter is required and must be a non-empty string")
+    .describe("Search query to find relevant Next.js documentation sections"),
   category: z
     .enum(["all", "getting-started", "guides", "api-reference", "architecture", "community"])
     .optional()
@@ -136,6 +139,7 @@ Provides access to comprehensive Next.js guides, API references, and best practi
     category = "all",
   }: z.infer<typeof nextjsDocsInputSchema>): Promise<string> => {
     // Step 1: Search MCP resources first (Next.js 16 knowledge base)
+    // Note: Arguments are now validated by Zod at the MCP server level before reaching here
     const mcpMatches = searchMcpResources(query)
 
     if (mcpMatches.length > 0) {