Passing Variables from Copilot Studio Agent to MCP Tool

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Posted on by TC-22010551-0

Is it possible to override an input to an MCP Tool with a variable, instead of determined by generative AI?

For example, if I want to pass the variable System.Conversation.Id to a tool, it would be better if this is filled automatically.

My particular use case needs the conversation id to find the subfolder of the Azure blob storage which corresponds to that chat session.

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Building Copilot Studio chatbots in Microsoft Teams

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Valantis 6,735 on at

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Hi @TC-22010551-0,

Yes you can override an MCP tool’s input with a variable (e.g., System.Conversation.Id) instead of letting AI infer it.

In Copilot Studio:

Open your MCP tool action.

Click the input (e.g., conversationId).

Change Fill using from “Dynamically fill” to Custom value.

Choose System.Conversation.Id from the variable picker.

If available, uncheck “Should prompt user.”

Result: The conversation ID is passed to your tool automatically no AI extraction, no user prompt.

- Your MCP tool gets System.Conversation.Id directly, so it can target the correct Azure Blob Storage subfolder.

Note: Copilot Studio doesn’t auto-map variables to MCP parameters, you must set Custom value manually.

Sources:

Microsoft Docs: Add tools to custom agents: https://learn.microsoft.com/en-us/microsoft-copilot-studio/advanced-plugin-actions

Microsoft Docs: Manage topic inputs and outputs: https://learn.microsoft.com/en-us/microsoft-copilot-studio/advanced-managing-topic-inputs-outputs

Microsoft Docs: Additional settings for inputs: https://learn.microsoft.com/en-us/microsoft-copilot-studio/advanced-additional-settings-topic-action-inputs

Let me know if that helped.

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Valantis 6,735 on at

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Hi @TC-22010551-0,

Just wanted to check in and see if everything is working now. If you still need any help, feel free to let me know.

Also, if the issue is resolved, it would be great if you could mark the answer as solved so others with the same question can find it easily.

Thanks and have a great day!

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