[BUG] ESM Module Compatibility Error: require() of ES Module 'pkce-challenge' not supported in MCP SDK

[KashiMoonactive]

Bug Description

Error when importing the pkce-challenge ESM module in a CommonJS environment. The MCP SDK is attempting to use require() to import an ES Module, which is not supported.

Reproduction Steps

Steps to reproduce the behavior:

1. Create a project using the MCP SDK
2. Install dependencies including @modelcontextprotocol/sdk and @langchain/mcp-adapters
3. Run the application
4. See error related to ES Module import

Expected Behavior

The application should successfully import dependencies and run without ESM/CommonJS compatibility errors.

Actual Behavior

An error occurs when attempting to use require() to import the ES Module pkce-challenge:

[0] /***/node_modules/@modelcontextprotocol/sdk/dist/cjs/client/auth.js:13
[0] const pkce_challenge_1 = __importDefault(require("pkce-challenge"));
[0]                                          ^
[0] 
[0] Error [ERR_REQUIRE_ESM]: require() of ES Module /***/node_modules/pkce-challenge/dist/index.node.js from /***/node_modules/@modelcontextprotocol/sdk/dist/cjs/client/auth.js not supported.
[0] Instead change the require of index.node.js in /***/node_modules/@modelcontextprotocol/sdk/dist/cjs/client/auth.js to a dynamic import() which is available in all CommonJS modules.
[0]     at Object.<anonymous> (***/node_modules/@modelcontextprotocol/sdk/dist/cjs/client/auth.js:13:42)
[0]     at Object.<anonymous> (***/node_modules/@modelcontextprotocol/sdk/dist/cjs/client/sse.js:6:19)
[0]     at Object.<anonymous> (***/node_modules/@langchain/mcp-adapters/dist/client.cjs:32:18)
[0]     at Object.<anonymous> (***/node_modules/@langchain/mcp-adapters/dist/index.cjs:4:19)
[0]     at Object.<anonymous> (***/node_modules/@langchain/mcp-adapters/index.cjs:1:18)
[0]     at Object.<anonymous> (***/dist/backend/game-architect-typescript.js:47:24)
[0]     at Object.<anonymous> (***/dist/backend/express-api-server.js:8:40) {
[0]   code: 'ERR_REQUIRE_ESM'
[0] }
[0] 
[0] Node.js v20.9.0

Environment

• OS: macOS,
• Node.js version: 20.9.0
• Package version: 0.3.4
• MCP SDK version: 1.7.0

Additional Context

Add any other context about the problem here, such as:

• Server implementation details
• Transport type (stdio, SSE)
• Any relevant logs

Possible Solution

The error message suggests changing the require() call to a dynamic import() in the MCP SDK's auth.js file. Options include:

1. Update the MCP SDK to use dynamic imports for ESM-only packages:

   const pkceChallengeModule = await import('pkce-challenge');
   const pkceChallenge = pkceChallengeModule.default;

2. Use a version of pkce-challenge that provides CommonJS support if available

3. Create a custom wrapper for pkce-challenge that handles the ESM/CommonJS interoperability

4. Configure the build system to handle ESM/CommonJS interoperability (using tools like webpack or babel)

[Pdash-exceeds]

It's a bug in @modelcontextprotocol/sdk . Workaround :

1. Patch this @modelcontextprotocol/sdk fails in CommonJS projects due to incompatible ESM-only dependency (pkce-challenge) modelcontextprotocol/typescript-sdk#217
2. Patch @langchain/mcp-adapters/dist/tools.cjs

@langchain+mcp-adapters+0.3.3.patch

[TimSusa]

what about using bun instead of node? In my case it will took care about this import nightmare

[benjamincburns]

The change you requested for this project was already implemented in 0.3.4, per #36. Please update to the latest version and open a new issue if you are still having CJS issues with that version.