Teach MCP clients the calendar's date conventions

mcp_svc/server.py

@@ -2,9 +2,42 @@
 
 mcp = MCPServer(
     name='orthocal',
-    instructions=(
-        'Look up Eastern Orthodox liturgical calendar data: feasts, fasting '
-        'rules, scripture readings, and lives of the saints for a given day, '
-        'or search for a saint by name.'
-    ),
+    instructions='''\
+Look up Eastern Orthodox liturgical calendar data: feasts, fasting rules,
+scripture readings, and lives of the saints for a given day, or search for a
+saint by name.
+
+Choosing tradition and calendar:
+- tradition=slavic follows OCA/ROCOR practice; tradition=greek follows Greek
+  Orthodox (GOARCH) and Antiochian practice. Ask, or infer from the user's
+  jurisdiction, when it matters -- feasts, readings, and fasting differ.
+- calendar=gregorian is the New (Revised Julian) calendar; calendar=julian is
+  the Old calendar used by ROCOR, most Slavic churches, Jerusalem, and Mount
+  Athos. Greek-tradition users are almost always on the New calendar.
+
+Dates:
+- get_day always takes the civil (Gregorian) date the user is living on. With
+  calendar=julian, the year/month/day in the result are the church-calendar
+  (Julian) date, which is 13 days earlier -- e.g. civil January 7 returns
+  December 25, the Nativity. Report the civil date to the user.
+- search_saints returns the fixed church-calendar month/day of each
+  commemoration. On the New calendar that is also the civil date. On the Old
+  calendar, add 13 days to get the civil date (1900-2099) before calling
+  get_day. Moveable feasts tied to Pascha are not found by search_saints.
+
+Workflow: to tell someone about a saint, call search_saints, then get_day on
+the resulting civil date for the full life (in stories) and the readings.
+
+Reading results:
+- summary_title is the best one-line name for the day.
+- For fasting, combine fast_level_desc with fast_exception_desc, or use
+  fast_abstentions for a plain list of foods to avoid. These reflect the
+  strict typikon; suggest the user follow their parish or spiritual father's
+  guidance on local practice.
+- abbreviated_reading_indices picks out the main readings (usually the
+  liturgy's Epistle and Gospel); use them for a short answer and the full
+  readings list when asked for everything.
+- Each reading's passage is a list of verses; stories are HTML, so strip
+  markup when quoting them.
+''',
 )

mcp_svc/tools.py

@@ -23,8 +23,8 @@ async def get_day(
     selects Slavic (OCA/ROCOR) or Greek (Antiochian/GOARCH) practice.
     translation selects the Bible translation for English readings --
     lxx2012-web (the default, a modern-English pairing of the Brenton
-    Septuagint and the World English Bible) or kjv (King James Version);
-    it has no effect on non-English content.
+    Septuagint and the World English Bible), kjv (King James Version), or
+    douay-rheims (Douay-Rheims); it has no effect on non-English content.
     """
 
     try: