Why the parameter work with JsonElement but not with Dictionary<string,object> ?

[andrew-at-v]

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Question Category

• Protocol Specification
• SDK Usage
• Server Implementation
• General Implementation
• Documentation
• Other

Your Question

When we create MCP server that has parameter Dictionary<string, object>
It does not send the parameter for whatever reason until i use JsonElement

Is this expected behavior?

[PederHP]

Can you show a code example? Is this a tool, a resource, a prompt, etc.? There isn't really enough information here for me to fully understand the nature of your problem and question.

[andrew-at-v]

It's a tool, for example

This is NOT working
for some reason agent always send "null" to metadata

[McpServerTool]
public async Task<string> GenerateTemplate(Dictionary<string,object> metadata){
...
}

This is working
The agent can send metadata

[McpServerTool]
public async Task<string> GenerateTemplate(JsonElement metadata){
...
}

[mikekistler]

@andrew-at-v I just tested the "NOT working" variant above and confirmed that an MCP server using the C# SDK correctly handles a metadata parameter with a Dictionary<string,object> value.

So perhaps what you mean is that the LLM you are using doesn't understand Dictionary<string,object> and requests that the metadata parameter value be set to null. That sounds like a problem with the LLM, or that there is not a sufficient description on the metadata parameter for it to figure out what to send. Your example doesn't show any description on the metadata parameter -- maybe that is the problem?