feat: natural language date shortcuts for litellm_cost()

Adds _resolve_date() helper that converts natural language shortcuts
into YYYY-MM-DD before calling the LiteLLM API.

Supported shortcuts:
- today, yesterday, tomorrow
- N days ago (e.g. "two days ago")
- monday-sunday (most recent occurrence)
- last monday-last sunday
- this week, last week
- this month, last month

Falls back to passthrough for already-formatted YYYY-MM-DD strings.

Updated README with new parameter documentation.

litellm_dashboard.py

@@ -10,6 +10,7 @@ licence: MIT
 """
 
 import requests
+from datetime import datetime, timedelta
 from pydantic import BaseModel, Field
 from typing import Optional
 
@@ -40,6 +41,76 @@ class Tools:
         """Get base URL, strip trailing slash."""
         return self.valves.litellm_url.rstrip("/")
 
+    def _resolve_date(self, date_str: str) -> str:
+        """Resolve natural language date shortcuts to YYYY-MM-DD.
+
+        Supports: today, yesterday, tomorrow, N days ago,
+        monday-sunday (this week), last monday-last sunday,
+        this week, last week, this month, last month.
+        Falls back to passthrough if already YYYY-MM-DD or unrecognized.
+        """
+        date_str = date_str.strip().lower()
+        today = datetime.utcnow().date()
+
+        # Direct shortcuts
+        if date_str == "today":
+            return today.isoformat()
+        if date_str == "yesterday":
+            return (today - timedelta(days=1)).isoformat()
+        if date_str == "tomorrow":
+            return (today + timedelta(days=1)).isoformat()
+
+        # "N days ago"
+        if "days ago" in date_str:
+            try:
+                n = int(date_str.split()[0])
+                return (today - timedelta(days=n)).isoformat()
+            except (ValueError, IndexError):
+                pass
+
+        # Day names — most recent occurrence (including today if it matches)
+        days = ["monday", "tuesday", "wednesday", "thursday", "friday", "saturday", "sunday"]
+        if date_str in days:
+            target_day = days.index(date_str)
+            days_back = (today.weekday() - target_day) % 7
+            return (today - timedelta(days=days_back)).isoformat()
+
+        # "last monday", "last tuesday", etc.
+        if date_str.startswith("last "):
+            day_part = date_str[5:].strip()
+            if day_part in days:
+                target_day = days.index(day_part)
+                days_back = (today.weekday() - target_day) % 7 + 7
+                return (today - timedelta(days=days_back)).isoformat()
+
+        # "this week" → Monday of this week
+        if date_str == "this week":
+            return (today - timedelta(days=today.weekday())).isoformat()
+
+        # "last week" → Monday of last week
+        if date_str == "last week":
+            return (today - timedelta(days=today.weekday() + 7)).isoformat()
+
+        # "this month" → 1st of this month
+        if date_str == "this month":
+            return today.replace(day=1).isoformat()
+
+        # "last month" → 1st of last month
+        if date_str == "last month":
+            if today.month == 1:
+                return today.replace(year=today.year - 1, month=12, day=1).isoformat()
+            return today.replace(month=today.month - 1, day=1).isoformat()
+
+        # Already YYYY-MM-DD — passthrough
+        try:
+            datetime.strptime(date_str, "%Y-%m-%d")
+            return date_str
+        except ValueError:
+            pass
+
+        # Unknown — return as-is (API will reject with clear error)
+        return date_str
+
     def litellm_health(self) -> str:
         """
         Check LiteLLM proxy health and authentication status.
@@ -123,17 +194,20 @@ class Tools:
     ) -> str:
         """
         Get LiteLLM cost breakdown for a date range.
-        :param start_date: Start date in YYYY-MM-DD format (e.g. "2026-06-01")
-        :param end_date: End date in YYYY-MM-DD format (e.g. "2026-06-04")
+        :param start_date: Start date — YYYY-MM-DD or natural language shortcut (e.g. "2026-06-01", "today", "yesterday", "monday", "last monday", "two days ago", "this week", "last month")
+        :param end_date: End date — YYYY-MM-DD or natural language shortcut
         :param hide_zero_spend: Hide models with sub-$0.001 spend (default False). Useful when free-tier or subscription models (e.g. Ollama Cloud) dominate the breakdown with high token counts but negligible cost.
         Returns formatted cost report with per-model and per-day breakdowns, token counts, cache hit rate, and request stats.
         """
         if not self.valves.litellm_master_key:
             return "❌ Master key required for cost data. Set the litellm_master_key valve."
 
+        resolved_start = self._resolve_date(start_date)
+        resolved_end = self._resolve_date(end_date)
+
         url = f"{self._base_url()}/user/daily/activity"
         headers = self._headers()
-        params = {"start_date": start_date, "end_date": end_date}
+        params = {"start_date": resolved_start, "end_date": resolved_end}
 
         try:
             resp = requests.get(url, headers=headers, params=params, timeout=30)