chore: switch to module ESNext + moduleResolution bundler

CLAUDE.md

@@ -36,7 +36,7 @@ Include what changed, why, and how to migrate. Search for related sections and g
 - **TypeScript**: Strict type checking, ES modules, explicit return types
 - **Naming**: PascalCase for classes/types, camelCase for functions/variables
 - **Files**: Lowercase with hyphens, test files with `.test.ts` suffix
-- **Imports**: ES module style, include `.js` extension, group imports logically
+- **Imports**: ES module style, no `.js` extension on relative imports (project uses `moduleResolution: bundler`), group imports logically
 - **Formatting**: 2-space indentation, semicolons required, single quotes preferred
 - **Testing**: Place tests under each package's `test/` directory (vitest only includes `test/**/*.test.ts`), use descriptive test names
 - **Comments**: JSDoc for public APIs, inline comments for complex logic

common/tsconfig/tsconfig.json

@@ -2,8 +2,8 @@
     "compilerOptions": {
         "target": "esnext",
         "lib": ["esnext"],
-        "module": "NodeNext",
-        "moduleResolution": "NodeNext",
+        "module": "ESNext",
+        "moduleResolution": "bundler",
         "noFallthroughCasesInSwitch": true,
         "noUncheckedIndexedAccess": true,
         "noImplicitOverride": true,

docs/client-quickstart.md

@@ -88,10 +88,10 @@
 ```json
 {
   "compilerOptions": {
     "target": "ES2023",
     "lib": ["ES2023"],
-    "module": "Node16",
-    "moduleResolution": "Node16",
+    "module": "ESNext",
+    "moduleResolution": "bundler",
     "outDir": "./build",
     "rootDir": "./src",
     "strict": true,
@@ -236,7 +236,8 @@
           messages,
         });
 
-        finalText.push(followUp.content[0].type === 'text' ? followUp.content[0].text : '');
+        const firstBlock = followUp.content[0];
+        finalText.push(firstBlock?.type === 'text' ? firstBlock.text : '');
       }
     }
 
@@ -284,13 +285,14 @@
 
 ```ts source="../examples/client-quickstart/src/index.ts#main"
 async function main() {
-  if (process.argv.length < 3) {
+  const serverScriptPath = process.argv[2];
+  if (!serverScriptPath) {
     console.log('Usage: node build/index.js <path_to_server_script>');
     return;
   }
   const mcpClient = new MCPClient();
   try {
-    await mcpClient.connectToServer(process.argv[2]);
+    await mcpClient.connectToServer(serverScriptPath);
 
     // Check if we have a valid API key to continue
     const apiKey = process.env.ANTHROPIC_API_KEY;

docs/server-quickstart.md

@@ -104,8 +104,8 @@ Create a `tsconfig.json` in the root of your project:
 {
   "compilerOptions": {
     "target": "ES2022",
-    "module": "Node16",
-    "moduleResolution": "Node16",
+    "module": "ESNext",
+    "moduleResolution": "bundler",
     "outDir": "./build",
     "rootDir": "./src",
     "strict": true,

examples/client-quickstart/package.json

@@ -15,6 +15,7 @@
         "@modelcontextprotocol/client": "workspace:^"
     },
     "devDependencies": {
+        "@modelcontextprotocol/tsconfig": "workspace:^",
         "@types/node": "^24.10.1",
         "typescript": "catalog:devTools"
     }

examples/client-quickstart/src/index.ts

@@ -116,7 +116,8 @@ class MCPClient {
           messages,
         });
 
-        finalText.push(followUp.content[0].type === 'text' ? followUp.content[0].text : '');
+        const firstBlock = followUp.content[0];
+        finalText.push(firstBlock?.type === 'text' ? firstBlock.text : '');
       }
     }
 
@@ -156,13 +157,14 @@ class MCPClient {
 
 //#region main
 async function main() {
-  if (process.argv.length < 3) {
+  const serverScriptPath = process.argv[2];
+  if (!serverScriptPath) {
     console.log('Usage: node build/index.js <path_to_server_script>');
     return;
   }
   const mcpClient = new MCPClient();
   try {
-    await mcpClient.connectToServer(process.argv[2]);
+    await mcpClient.connectToServer(serverScriptPath);
 
     // Check if we have a valid API key to continue
     const apiKey = process.env.ANTHROPIC_API_KEY;

examples/client-quickstart/tsconfig.json

@@ -1,15 +1,11 @@
 {
+    "extends": "@modelcontextprotocol/tsconfig",
     "compilerOptions": {
-        "target": "ES2023",
-        "lib": ["ES2023"],
-        "module": "Node16",
-        "moduleResolution": "Node16",
         "outDir": "./build",
         "rootDir": "./src",
-        "strict": true,
-        "esModuleInterop": true,
-        "skipLibCheck": true,
-        "forceConsistentCasingInFileNames": true,
+        "declaration": false,
+        "declarationMap": false,
+        "types": ["node"],
         "paths": {
             "@modelcontextprotocol/client": ["./node_modules/@modelcontextprotocol/client/src/index.ts"],
             "@modelcontextprotocol/client/stdio": ["./node_modules/@modelcontextprotocol/client/src/stdio.ts"],

examples/client/src/elicitationUrlExample.ts

@@ -27,7 +27,7 @@ import {
 } from '@modelcontextprotocol/client';
 import open from 'open';
 
-import { InMemoryOAuthClientProvider } from './simpleOAuthClientProvider.js';
+import { InMemoryOAuthClientProvider } from './simpleOAuthClientProvider';
 
 // Set up OAuth (required for this example)
 const OAUTH_CALLBACK_PORT = 8090; // Use different port than auth server (3001)

examples/client/src/simpleOAuthClient.ts

@@ -8,7 +8,7 @@ import type { CallToolResult, ListToolsRequest, OAuthClientMetadata } from '@mod
 import { Client, StreamableHTTPClientTransport, UnauthorizedError } from '@modelcontextprotocol/client';
 import open from 'open';
 
-import { InMemoryOAuthClientProvider } from './simpleOAuthClientProvider.js';
+import { InMemoryOAuthClientProvider } from './simpleOAuthClientProvider';
 
 // Configuration
 const DEFAULT_SERVER_URL = 'http://localhost:3000/mcp';

examples/server-quickstart/package.json

@@ -15,6 +15,7 @@
         "zod": "catalog:runtimeShared"
     },
     "devDependencies": {
+        "@modelcontextprotocol/tsconfig": "workspace:^",
         "@types/node": "^24.10.1",
         "typescript": "catalog:devTools"
     }

examples/server-quickstart/tsconfig.json

@@ -1,14 +1,11 @@
 {
+    "extends": "@modelcontextprotocol/tsconfig",
     "compilerOptions": {
-        "target": "ES2022",
-        "module": "Node16",
-        "moduleResolution": "Node16",
         "outDir": "./build",
         "rootDir": "./src",
-        "strict": true,
-        "esModuleInterop": true,
-        "skipLibCheck": true,
-        "forceConsistentCasingInFileNames": true,
+        "declaration": false,
+        "declarationMap": false,
+        "types": ["node"],
         "paths": {
             "@modelcontextprotocol/server": ["./node_modules/@modelcontextprotocol/server/src/index.ts"],
             "@modelcontextprotocol/server/stdio": ["./node_modules/@modelcontextprotocol/server/src/stdio.ts"],

examples/server/src/elicitationUrlExample.ts

@@ -19,7 +19,7 @@ import type { Request, Response } from 'express';
 import express from 'express';
 import * as z from 'zod/v4';
 
-import { InMemoryEventStore } from './inMemoryEventStore.js';
+import { InMemoryEventStore } from './inMemoryEventStore';
 
 // Create an MCP server with implementation details
 const getServer = () => {

examples/server/src/simpleStreamableHttp.ts

@@ -16,7 +16,7 @@ import cors from 'cors';
 import type { Request, Response } from 'express';
 import * as z from 'zod/v4';
 
-import { InMemoryEventStore } from './inMemoryEventStore.js';
+import { InMemoryEventStore } from './inMemoryEventStore';
 
 // Check for OAuth flag
 const useOAuth = process.argv.includes('--oauth');

examples/server/src/ssePollingExample.ts

@@ -21,7 +21,7 @@ import { McpServer } from '@modelcontextprotocol/server';
 import cors from 'cors';
 import type { Request, Response } from 'express';
 
-import { InMemoryEventStore } from './inMemoryEventStore.js';
+import { InMemoryEventStore } from './inMemoryEventStore';
 
 // Create a fresh MCP server per client connection to avoid shared state between clients
 const getServer = () => {

examples/shared/src/authServer.ts

@@ -18,8 +18,8 @@ import cors from 'cors';
 import type { Request, Response as ExpressResponse, Router } from 'express';
 import express from 'express';
 
-import type { DemoAuth } from './auth.js';
-import { createDemoAuth, DEMO_USER_CREDENTIALS } from './auth.js';
+import type { DemoAuth } from './auth';
+import { createDemoAuth, DEMO_USER_CREDENTIALS } from './auth';
 
 export interface SetupAuthServerOptions {
     authServerUrl: URL;

examples/shared/src/index.ts

@@ -1,7 +1,7 @@
 // Auth configuration
-export type { CreateDemoAuthOptions, DemoAuth } from './auth.js';
-export { createDemoAuth } from './auth.js';
+export type { CreateDemoAuthOptions, DemoAuth } from './auth';
+export { createDemoAuth } from './auth';
 
 // Auth server setup + demo token verifier (pass to `requireBearerAuth` from @modelcontextprotocol/express)
-export type { SetupAuthServerOptions } from './authServer.js';
-export { createProtectedResourceMetadataRouter, demoTokenVerifier, getAuth, setupAuthServer } from './authServer.js';
+export type { SetupAuthServerOptions } from './authServer';
+export { createProtectedResourceMetadataRouter, demoTokenVerifier, getAuth, setupAuthServer } from './authServer';

examples/shared/test/demoInMemoryOAuthProvider.test.ts

@@ -9,8 +9,8 @@
 
 import { describe, expect, it } from 'vitest';
 
-import type { CreateDemoAuthOptions } from '../src/auth.js';
-import { createDemoAuth } from '../src/auth.js';
+import type { CreateDemoAuthOptions } from '../src/auth';
+import { createDemoAuth } from '../src/auth';
 
 describe('createDemoAuth', () => {
     const validOptions: CreateDemoAuthOptions = {

packages/client/src/client/auth.examples.ts

@@ -9,8 +9,8 @@
 
 import type { AuthorizationServerMetadata } from '@modelcontextprotocol/core';
 
-import type { OAuthClientProvider } from './auth.js';
-import { fetchToken } from './auth.js';
+import type { OAuthClientProvider } from './auth';
+import { fetchToken } from './auth';
 
 /**
  * Base class providing no-op implementations of required OAuthClientProvider methods.

packages/client/src/client/authExtensions.examples.ts

@@ -7,8 +7,8 @@
  * @module
  */
 
-import { ClientCredentialsProvider, createPrivateKeyJwtAuth, PrivateKeyJwtProvider } from './authExtensions.js';
-import { StreamableHTTPClientTransport } from './streamableHttp.js';
+import { ClientCredentialsProvider, createPrivateKeyJwtAuth, PrivateKeyJwtProvider } from './authExtensions';
+import { StreamableHTTPClientTransport } from './streamableHttp';
 
 /**
  * Example: Creating a private key JWT authentication function.

packages/client/src/client/authExtensions.ts

@@ -8,7 +8,7 @@
 import type { FetchLike, OAuthClientInformation, OAuthClientMetadata, OAuthTokens } from '@modelcontextprotocol/core';
 import type { CryptoKey, JWK } from 'jose';
 
-import type { AddClientAuthentication, OAuthClientProvider } from './auth.js';
+import type { AddClientAuthentication, OAuthClientProvider } from './auth';
 
 /**
  * Helper to produce a `private_key_jwt` client authentication function.

packages/client/src/client/client.examples.ts

@@ -9,10 +9,10 @@
 
 import type { Prompt, Resource, Tool } from '@modelcontextprotocol/core';
 
-import { Client } from './client.js';
-import { SSEClientTransport } from './sse.js';
-import { StdioClientTransport } from './stdio.js';
-import { StreamableHTTPClientTransport } from './streamableHttp.js';
+import { Client } from './client';
+import { SSEClientTransport } from './sse';
+import { StdioClientTransport } from './stdio';
+import { StreamableHTTPClientTransport } from './streamableHttp';
 
 /**
  * Example: Using listChanged to automatically track tool and prompt updates.

packages/client/src/client/client.ts

@@ -65,7 +65,7 @@ import {
     SdkErrorCode
 } from '@modelcontextprotocol/core';
 
-import { ExperimentalClientTasks } from '../experimental/tasks/client.js';
+import { ExperimentalClientTasks } from '../experimental/tasks/client';
 
 /**
  * Elicitation default application helper. Applies defaults to the `data` based on the `schema`.

packages/client/src/client/crossAppAccess.ts

@@ -11,8 +11,8 @@
 import type { FetchLike } from '@modelcontextprotocol/core';
 import { IdJagTokenExchangeResponseSchema, OAuthErrorResponseSchema, OAuthTokensSchema } from '@modelcontextprotocol/core';
 
-import type { ClientAuthMethod } from './auth.js';
-import { applyClientAuthentication, discoverAuthorizationServerMetadata } from './auth.js';
+import type { ClientAuthMethod } from './auth';
+import { applyClientAuthentication, discoverAuthorizationServerMetadata } from './auth';
 
 /**
  * Options for requesting a JWT Authorization Grant via RFC 8693 Token Exchange.

packages/client/src/client/middleware.examples.ts

@@ -7,8 +7,8 @@
  * @module
  */
 
-import type { Middleware } from './middleware.js';
-import { applyMiddlewares, createMiddleware } from './middleware.js';
+import type { Middleware } from './middleware';
+import { applyMiddlewares, createMiddleware } from './middleware';
 
 // Stubs for hypothetical application middleware
 declare function withOAuth(provider: unknown, url: string): Middleware;

packages/client/src/client/middleware.ts

@@ -1,7 +1,7 @@
 import type { FetchLike } from '@modelcontextprotocol/core';
 
-import type { OAuthClientProvider } from './auth.js';
-import { auth, extractWWWAuthenticateParams, UnauthorizedError } from './auth.js';
+import type { OAuthClientProvider } from './auth';
+import { auth, extractWWWAuthenticateParams, UnauthorizedError } from './auth';
 
 /**
  * Middleware function that wraps and enhances fetch functionality.

packages/client/src/client/sse.ts

@@ -3,8 +3,8 @@ import { createFetchWithInit, JSONRPCMessageSchema, normalizeHeaders, SdkError,
 import type { ErrorEvent, EventSourceInit } from 'eventsource';
 import { EventSource } from 'eventsource';
 
-import type { AuthProvider, OAuthClientProvider } from './auth.js';
-import { adaptOAuthProvider, auth, extractWWWAuthenticateParams, isOAuthClientProvider, UnauthorizedError } from './auth.js';
+import type { AuthProvider, OAuthClientProvider } from './auth';
+import { adaptOAuthProvider, auth, extractWWWAuthenticateParams, isOAuthClientProvider, UnauthorizedError } from './auth';
 
 export class SseError extends Error {
     constructor(

packages/client/src/client/streamableHttp.examples.ts

@@ -9,7 +9,7 @@
 
 /* eslint-disable unicorn/consistent-function-scoping -- examples must live inside region blocks */
 
-import type { ReconnectionScheduler } from './streamableHttp.js';
+import type { ReconnectionScheduler } from './streamableHttp';
 
 // Stub for a hypothetical platform-specific background scheduling API
 declare const platformBackgroundTask: {

packages/client/src/client/streamableHttp.ts

@@ -14,8 +14,8 @@ import {
 } from '@modelcontextprotocol/core';
 import { EventSourceParserStream } from 'eventsource-parser/stream';
 
-import type { AuthProvider, OAuthClientProvider } from './auth.js';
-import { adaptOAuthProvider, auth, extractWWWAuthenticateParams, isOAuthClientProvider, UnauthorizedError } from './auth.js';
+import type { AuthProvider, OAuthClientProvider } from './auth';
+import { adaptOAuthProvider, auth, extractWWWAuthenticateParams, isOAuthClientProvider, UnauthorizedError } from './auth';
 
 // Default reconnection options for StreamableHTTP connections
 const DEFAULT_STREAMABLE_HTTP_RECONNECTION_OPTIONS: StreamableHTTPReconnectionOptions = {

packages/client/src/experimental/index.ts

@@ -10,4 +10,4 @@
  * @experimental
  */
 
-export * from './tasks/client.js';
+export * from './tasks/client';

packages/client/src/experimental/tasks/client.examples.ts

@@ -9,7 +9,7 @@
 
 import type { RequestOptions } from '@modelcontextprotocol/core';
 
-import type { Client } from '../../client/client.js';
+import type { Client } from '../../client/client';
 
 /**
  * Example: Using callToolStream to execute a tool with task lifecycle events.

packages/client/src/experimental/tasks/client.ts

@@ -28,7 +28,7 @@ import {
     ProtocolErrorCode
 } from '@modelcontextprotocol/core';
 
-import type { Client } from '../../client/client.js';
+import type { Client } from '../../client/client';
 
 /**
  * Internal interface for accessing {@linkcode Client}'s private methods.