There is currently no way with the current MCP tools, particularly the search workspace and tasks, to filter by a custom field's value. This is possible within the API so it would be nice to have parity with the API. Currently the only way to see a custom field in the MCP tool is to get task details, but that returns extra tokens and eats away at context. In Copilot Studio, it throws an error when retrieving multiple task details, so even client-side filtering is unrealistic for modern AI tools.