[Bug]: MCP error -32602: Invalid arguments for tool...

[jleonelion]

Version

About two weeks ago, I configured my Claude Desktop to use the Mongo MCP (via Docker) and it's been working great!

At some point in the last day or two, this setup started having problems and now fails regularly. I didn't change any of my configuration files but I suspect auto-updates may have crept in. It looks like Claude is not sending the necessary arguments when making tool calls, resulting in logs like:

025-07-23T06:11:18.838Z [collectibles-mongodb] [info] Message from client: {"method":"tools/call","params":{"name":"list-collections"},"jsonrpc":"2.0","id":5} { metadata: undefined }
2025-07-23T06:11:18.842Z [collectibles-mongodb] [info] Message from server: {"jsonrpc":"2.0","id":5,"error":{"code":-32602,"message":"MCP error -32602: Invalid arguments for tool list-collections: [\n  {\n    \"code\": \"invalid_type\",\n    \"expected\": \"string\",\n    \"received\": \"undefined\",\n    \"path\": [\n      \"database\"\n    ],\n    \"message\": \"Required\"\n  }\n]"}} { metadata: undefined }

I initially thought the problem was related to updates in the "latest" version of the docker image hosting the MCP server. After trying older versions of the image (ex. mongodb/mongodb-mcp-server:0.1.3-2025-07-09) the problem persists.

I also tried using different models (ex. Claude Sonnet 4, Claude Sonnet 3.7, Claude Haiku 3.5) and I continue to see regular errors.

• list-databases works consistently (but that has not arguments)
• list-collections works most of the time, but it does fail (see logs above)
• count intermittently fails
• find frequently fails

I haven't exercised every tool, but I think you get the point. The difficult thing to nail down is this doesn't happen every time, but it does happen frequently enough to make it unusable.

What could be causing this?

App

• Cursor
• Windsurf
• VSCode
• VSCode Insiders
• Claude Desktop
• Other

Affected Models (if applicable)

• Claude 3.5 Sonnet
• Claude 3.7 Sonnet
• GPT-4a
• o4-mini
• Other

Bug Description

Tool calls are intermittently failing with errors and a response Error executing code: Cannot convert undefined or null to object

[github-actions]

Thanks for opening this issue. The ticket MCP-69 was created for internal tracking.

[jleonelion]

Update on this issue. Today things are working much better!
I am using mongodb/mongodb-mcp-server:0.1.3-2025-07-09
This was giving me problems yesterday. I'll change to using "latest" once I finish what I'm working on.

Maybe LLMs get tired too?

[gagik]

Awesome! I'm glad the issues managed to resolve itself 🥳

Yeah, behavior of LLMs can be quite unpredictable at times, might depend on the agent client updates as well. Going to close this but if you notice a reoccurring pattern of broken tools feel free to follow-up.