MCP: LLMs unable to properly escape JSON passed to MCP

[henrikmcgee]

App Version

3.11.14

API Provider

OpenRouter

Model Used

Claude 3.7 Sonnet and others

Actual vs. Expected Behavior

Background: I have a latex syntax checker MCP to prevent the LLM from outputting invalid code.
Whenever I try to pass python or latex or whatever code to the MCP, the LLM is unable to properly escape the input.
This causes a loop and after a few attempts, roo will give up. Roo should ALWAYS escape the string and never ask the LLM to do it. Even frontier LLMs fail with properly escaping long code strings.

example of a failing MCP-call:
{
"prompt": "<input_data>
39 | \stepcounter{fragenummer}
\arabic{fragenummer}. & \multicolumn{1}{|p{12cm}|}{\raggedright #1 } & \ifthenelse{#2=1}{{
\color{blue}{X}
}}{} & \ifthenelse{#2=1}{}{
\color{blue}{X}
etc...
}

Result: Roo tried to use verify_latex with an invalid JSON argument. Retrying...

To summarize: It NEVER works whenever I pass code of non-trivial length, even with frontier LLMs. Roo needs to escape this, the LLM should never be asked to escape. Alternatively use a different method to pass data to the mcp.

Detailed Steps to Reproduce

1.) Install MCP which requires large chunks of python or latex to be passed to it.
2.) Make the LLM execute it.
3.) Stuck in loop.

Relevant API Request Output

Additional Context

No response

[dosubot]

Hello @henrikmcgee! I'm Dosu, your friendly bot here to help you solve bugs, answer questions, and guide you in becoming a contributor. I'm here while you wait for a human maintainer. Let's tackle this together!

The issue you're experiencing seems to be related to JSON escaping when passing code snippets to the MCP. Unfortunately, I couldn't find specific details in the Roo Code repository or documentation about how JSON escaping is handled for code snippets passed to the MCP. However, based on your description, it appears that the current implementation relies on the LLM to perform JSON escaping, which is causing problems with longer code strings.

Here are a few suggestions that might help address this issue:

1. Manual Escaping: Consider manually escaping the JSON strings before passing them to the MCP. This can be done using standard JSON libraries in your programming environment to ensure that all special characters are properly escaped.

2. Preprocessing: Implement a preprocessing step in your workflow where code snippets are sanitized and escaped before being sent to the MCP. This can help avoid relying on the LLM for escaping.

3. Alternative Data Passing Methods: Explore alternative methods for passing data to the MCP that do not rely on JSON, if feasible. This might involve using different serialization formats or communication protocols that handle complex data structures more robustly.

4. Error Handling: Enhance error handling mechanisms to catch and address JSON parsing errors more effectively, potentially logging detailed error messages for debugging.

If these suggestions don't resolve the issue, it might be worth checking for any open issues or discussions in the Roo Code repository that might address this problem or provide additional insights.

To continue talking to Dosu, mention @dosu.

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[robertheadley]

I was already updating something I had previously worked on related to MCPs, so I should be able to include the fix for this.