MCP puppeteer server stack size limit

[michnovka]

What happened?

Taking screenshots with puppeteer often does not work as I hit:

librechat-api          | 2025-02-08T22:04:39.359Z debug: [MCP][puppeteer] Transport sending: {"method":"tools/call","params":{"name":"puppeteer_navigate","arguments":{"url":"https://www.seznam.cz"}},"jsonrpc... [truncated]
librechat-api          | 2025-02-08T22:04:46.252Z debug: [MCP][puppeteer] Transport sending: {"method":"tools/call","params":{"name":"puppeteer_screenshot","arguments":{"name":"seznam_homepage_full_retry","s... [truncated]
librechat-api          | 2025-02-08T22:05:05.148Z error: puppeteer_screenshot MCP server tool call failed Maximum call stack size exceeded

I see in mcp server that it sends back response (base64 encoded large response) - but the action never finishes in librechat. And in log it complains about the stack size

Steps to Reproduce

1. use MCP with puppeteer
2. ask it to take SS with very high resolution

What browsers are you seeing the problem on?

No response

Relevant log output

Screenshots

No response

Code of Conduct

• I agree to follow this project's Code of Conduct

[danny-avila]

Seems like a bug on Puppeteer side, note that that MCP Server is more of a prototype made by the Anthropic devs

[michnovka]

Why do you say its puppeteer bug, I see in its log it replies. But its HUGE reply. Id say the bug is on Librechat side as it cant handle reply that big

[HenrikGustafsson-SVT]

Could it be related to the Zod version? I have a similar issue where a large base64 encoded image returned from an MCP-tool causes an error. Below is the call stack logs from LibreChat.

{"level":"error","message":"[MCP][User: 68905619539d3039ee377bd5][mcp-comfy-ui] Error calling \"text_to_image\" MCP tool: Maximum call stack size exceeded",
  "stack":"RangeError: Maximum call stack size exceeded\n
at RegExp.test (<anonymous>)\n    
at ZodString._parse (/app/node_modules/zod/dist/cjs/v3/types.js:788:34)\n
at ZodObject._parse (/app/node_modules/zod/dist/cjs/v3/types.js:1981:37)\n
at ZodObject._parseS...","timestamp":"2025-08-05T08:04:56.781Z"}

colinhacks/zod#4283

LibreChat seems to be using an older version of Zod 3.22.4, and the issue mentioned above was patched in May 2025.
@danny-avila