Error: Received tool input did not match expected schema at Proxy.call

Questions
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1

Describe the problem/error/question

I get the following error when my AI Agent attempts to communicate with my MCP Server tool.

Error: Received tool input did not match expected schema at Proxy.call

n8n version

1.102.3 (Self Hosted)

Stack trace

Error: Received tool input did not match expected schema at Proxy.call (/usr/local/lib/node_modules/n8n/node_modules/.pnpm/@langchain+core@0.3.61_openai@5.8.1_ws@8.17.1_zod@3.25.67_/node_modules/@langchain/core/dist/tools/index.cjs:117:23) at processTicksAndRejections (node:internal/process/task_queues:105:5)

I am suspecting its the MCP Server but I am unable to see what request it sent to the MCP Server.

How can I debug this?

The reason I think its the MCP is because I have the same workflow communicating with different MCP Servers for the same request and they both work fine.

I am testing the MongoDB MCP Server in public preview and my specific request gives me this issue.

Any hint is appreciated.

Thanks!

2

you can add code node in between to log output or in add option make Return Intermediate Steps to on to see what is being sent.

4

I added the option on my AI Agent to Return Intermediate Steps (checked it) and it outputs nothing more than then error mentioned in my post.

I will try the other option you mentioned. Thanks!

UPDATE I had to select continue instead of stop on error for it to give me the intermediate steps.