From a563e447aa23b526c1bf2035e6fb4e12e5f918f4 Mon Sep 17 00:00:00 2001
From: Matt Carey <mcarey@cloudflare.com>
Date: Fri, 28 Nov 2025 12:49:03 +0000
Subject: [PATCH] fix: update registerTool signature for proper typed
 ToolCallback

Swap generic type parameters and make InputArgs default to undefined,
  so callbacks are properly typed as (extra) => Result when no inputSchema
  is provided, eliminating the need for `as const` workarounds.

Co-Authored-By: Gavin <gching@users.noreply.github.com>
---
 src/server/mcp.test.ts | 24 ++++++++++++------------
 src/server/mcp.ts      |  2 +-
 2 files changed, 13 insertions(+), 13 deletions(-)

diff --git a/src/server/mcp.test.ts b/src/server/mcp.test.ts
index 2ad40ba5a..aa9a1477d 100644
--- a/src/server/mcp.test.ts
+++ b/src/server/mcp.test.ts
@@ -639,7 +639,7 @@ describe.each(zodTestMatrix)('$zodVersionLabel', (entry: ZodMatrixEntry) => {
                 async () => ({
                     content: [
                         {
-                            type: 'text' as const,
+                            type: 'text',
                             text: 'Test response'
                         }
                     ]
@@ -694,7 +694,7 @@ describe.each(zodTestMatrix)('$zodVersionLabel', (entry: ZodMatrixEntry) => {
                 async () => ({
                     content: [
                         {
-                            type: 'text' as const,
+                            type: 'text',
                             text: 'Test response'
                         }
                     ]
@@ -876,7 +876,7 @@ describe.each(zodTestMatrix)('$zodVersionLabel', (entry: ZodMatrixEntry) => {
                     }
                 },
                 async () => ({
-                    content: [{ type: 'text' as const, text: 'Test response' }]
+                    content: [{ type: 'text', text: 'Test response' }]
                 })
             );
 
@@ -1928,7 +1928,7 @@ describe.each(zodTestMatrix)('$zodVersionLabel', (entry: ZodMatrixEntry) => {
                 {
                     description: 'A valid tool name'
                 },
-                async () => ({ content: [{ type: 'text' as const, text: 'Success' }] })
+                async () => ({ content: [{ type: 'text', text: 'Success' }] })
             );
 
             // Test tool name with warnings (starts with dash)
@@ -1937,7 +1937,7 @@ describe.each(zodTestMatrix)('$zodVersionLabel', (entry: ZodMatrixEntry) => {
                 {
                     description: 'A tool name that generates warnings'
                 },
-                async () => ({ content: [{ type: 'text' as const, text: 'Success' }] })
+                async () => ({ content: [{ type: 'text', text: 'Success' }] })
             );
 
             // Test invalid tool name (contains spaces)
@@ -1946,7 +1946,7 @@ describe.each(zodTestMatrix)('$zodVersionLabel', (entry: ZodMatrixEntry) => {
                 {
                     description: 'An invalid tool name'
                 },
-                async () => ({ content: [{ type: 'text' as const, text: 'Success' }] })
+                async () => ({ content: [{ type: 'text', text: 'Success' }] })
             );
 
             // Verify that warnings were issued (both for warnings and validation failures)
@@ -3894,7 +3894,7 @@ describe.each(zodTestMatrix)('$zodVersionLabel', (entry: ZodMatrixEntry) => {
 
             // Tool 1: Only name
             mcpServer.tool('tool_name_only', async () => ({
-                content: [{ type: 'text' as const, text: 'Response' }]
+                content: [{ type: 'text', text: 'Response' }]
             }));
 
             // Tool 2: Name and annotations.title
@@ -3905,7 +3905,7 @@ describe.each(zodTestMatrix)('$zodVersionLabel', (entry: ZodMatrixEntry) => {
                     title: 'Annotations Title'
                 },
                 async () => ({
-                    content: [{ type: 'text' as const, text: 'Response' }]
+                    content: [{ type: 'text', text: 'Response' }]
                 })
             );
 
@@ -3917,7 +3917,7 @@ describe.each(zodTestMatrix)('$zodVersionLabel', (entry: ZodMatrixEntry) => {
                     description: 'Tool with regular title'
                 },
                 async () => ({
-                    content: [{ type: 'text' as const, text: 'Response' }]
+                    content: [{ type: 'text', text: 'Response' }]
                 })
             );
 
@@ -3932,7 +3932,7 @@ describe.each(zodTestMatrix)('$zodVersionLabel', (entry: ZodMatrixEntry) => {
                     }
                 },
                 async () => ({
-                    content: [{ type: 'text' as const, text: 'Response' }]
+                    content: [{ type: 'text', text: 'Response' }]
                 })
             );
 
@@ -5009,7 +5009,7 @@ describe.each(zodTestMatrix)('$zodVersionLabel', (entry: ZodMatrixEntry) => {
                     description: 'Tool with regular title'
                 },
                 async () => ({
-                    content: [{ type: 'text' as const, text: 'Response' }]
+                    content: [{ type: 'text', text: 'Response' }]
                 })
             );
 
@@ -5024,7 +5024,7 @@ describe.each(zodTestMatrix)('$zodVersionLabel', (entry: ZodMatrixEntry) => {
                     }
                 },
                 async () => ({
-                    content: [{ type: 'text' as const, text: 'Response' }]
+                    content: [{ type: 'text', text: 'Response' }]
                 })
             );
 
diff --git a/src/server/mcp.ts b/src/server/mcp.ts
index 68a81764a..c097ae531 100644
--- a/src/server/mcp.ts
+++ b/src/server/mcp.ts
@@ -1030,7 +1030,7 @@ export class McpServer {
     /**
      * Registers a tool with a config object and callback.
      */
-    registerTool<InputArgs extends ZodRawShapeCompat | AnySchema, OutputArgs extends ZodRawShapeCompat | AnySchema>(
+    registerTool<OutputArgs extends ZodRawShapeCompat | AnySchema, InputArgs extends undefined | ZodRawShapeCompat | AnySchema = undefined>(
         name: string,
         config: {
             title?: string;