Agents struggle with time zones

[rockfordlhotka]

One issue I am finding, is that agents (LLMs in general) struggle with time zones and date/time math. Specifically, when getting calendar information via calendar-mcp, agents seem to frequently "see" events from different calendars in different time zones, and then they try to compensate, and often end up thinking events are hours off from the actual times.

I am thinking that the MCP tools for calendar operations should require a time zone parameter, so the consuming agent can (is forced to) tell calendar-mcp what time zone should be used, and allow our deterministic code here to do any time zone translations.

With this change, all date/time values will be returned twice - in UTC and the specified "local" time zone. For example:

{
  "start_utc": "2026-03-04T15:00:00Z",
  "start_local": "2026-03-04T09:00:00",
  "timezone": "America/Chicago"
}