n8n MCP Node - Cannot Connect

[rolender2]

Tying to connect to a local mongodb via a local n8n server through a MCP node. Getting the following error:

Failed to execute operation: Failed to parse tool parameters: Tool parameters must be a JSON object. Make sure the parameters are valid JSON.

JSON:

[
{
"mongodb":
"connect-mongodb",
"Tool_Parameters":
[
"mongodb://localhost:27017",
"validateConnection"
]
}
]

any thoughts?

[LastryCoding]

The issue comes from your MCP tool configuration. Your Tool_Parameters must be a valid JSON object, like this:

{{ $fromAI('Tool_Parameters', `Use tool parameters here`, 'json', null) }}

Make sure to pre-prompt your model to follow a Record<string, string> format; otherwise, you'll get "invalid schema" errors.

Additionally, since Tool_Parameters is defined this way, even a tool without parameters (e.g., list-collections) will still include a Tool_Parameters: {} or null key, which can cause an error.

Solution: Create two execute tools – one with parameters and one without – and guide your model to use the appropriate one.

Note: It would have been better if parameters were simply ignored for tools without parameters instead of throwing an error.