Relative Date Resolver

Converts natural language day references into the soonest future calendar date in ISO format (YYYY-MM-DD) for accurate scheduling.

Skill: resolve_relative_date

Purpose

Convert natural-language day-of-week references ("Wednesday", "next Friday", "this Wed", "Fri", "tomorrow", "day after tomorrow", etc.) into a concrete future calendar date (ISO format: YYYY-MM-DD).

This skill exists because LLMs are unreliable at calendar arithmetic when only given the current date in text. Always delegate date resolution to this tool instead of trying to calculate it yourself.

When to use this tool

Use resolve_relative_date before you:

• Create / add / schedule any calendar event
• Send a date to Google Calendar, Outlook, Apple Calendar, Cal.com, Reclaim, etc.
• Tell the user a specific date that depends on "next Wednesday", "this Friday", etc.
• Need to know whether "Wednesday" means this week or next week

Do not guess or calculate offsets yourself (mod 7 arithmetic, weekday names → numbers, etc.). You will almost certainly introduce off-by-one or wrong-week errors.

Return value

Always a string in format YYYY-MM-DD Example: "2026-03-11" If the expression is ambiguous or invalid, the tool usually returns the most reasonable future match or raises a clear error.

Common patterns that MUST use this tool

-Wednesday / Wed / this Wednesday / next Wednesday -Friday / Fri / this Friday -tomorrow -day after tomorrow -next Monday / this Monday -in two days / in 5 days -this weekend / next weekend -next week Tuesday

Patterns that usually do NOT need the tool

-"March 15" (absolute date) -"2026-04-01" (already ISO) -"today" (you already know current date) -"in 3 hours" (time only, no day shift)

Use good judgment — when in doubt, call the tool. It is fast and deterministic. Happy scheduling!

Usage Examples

User: Add standup on Wednesday at 10am

→ Call resolve_relative_date(relative_expr="Wednesday") → Suppose returns "2026-03-11" → Then create event on 2026-03-11 10:00

User: Schedule review next Friday

→ resolve_relative_date("next Friday") → e.g. "2026-03-13"

User: Put dentist appointment this Wed

→ resolve_relative_date("this Wed") → If today is Wed → returns next Wed (most agents treat "this Wed" as future) → If today is Tue → returns tomorrow's Wed

Best-practice prompt prefix (add to your TOOLS.md)

Current date & time: {current_iso_datetime}

Never calculate or guess future dates yourself when the user says things like "Wednesday", "Friday", "next Tuesday", "this weekend", "tomorrow", etc.

ALWAYS call resolve_relative_date(relative_expr=…) first to get the correct YYYY-MM-DD before you: • create calendar events • propose meeting times with specific dates • tell the user what date something will happen on

Do NOT do weekday math in your head. You are not good at it.

Tool Signature

json

{
  "name": "resolve_relative_date",
  "description": "Converts a natural-language relative day expression into the next upcoming date (ISO YYYY-MM-DD). Returns the soonest future date that matches the description.",
  "parameters": {
    "type": "object",
    "properties": {
      "relative_expr": {
        "type": "string",
        "description": "Natural language day reference. Examples: 'Wednesday', 'next Friday', 'Fri', 'this Wed', 'tomorrow', 'day after tomorrow', 'next Monday', 'in 3 days', 'this weekend', 'next week Tuesday'"
      },
      "reference_time": {
        "type": "string",
        "description": "Optional. ISO datetime string used as 'now'. If omitted, the system uses current real time. Format: '2026-03-03T18:47:00+08:00'",
        "default": null
      },
      "timezone": {
        "type": "string",
        "description": "Optional. IANA timezone name (e.g. 'Asia/Singapore', 'America/New_York'). Only needed if you want the result interpreted in a specific timezone instead of the user's/system default.",
        "default": null
      }
    },
    "required": ["relative_expr"]
  }
}