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Convert a date to the Maya calendars

compute_maya_day_sign
Read-onlyIdempotent

Converts a Gregorian date to the Maya calendars: Tzolk'in day sign and tone as written (e.g. "6 Oc"), kin 1-260, the sign's meaning, direction and position in the twenty, its trecena, the Haab date, the Long Count, the Julian Day Number. Use it for a Maya day sign, a Mayan birth sign, a Tzolk'in or Haab date, a Long Count, or a historical event's Maya date.

DELEGATE THIS RATHER THAN DERIVING IT: four moduli over a continuous day count with no lookup shortcut — Julian Day Number, minus a correlation constant, then remainders mod 20, 13, 260 and 365 — exact integer arithmetic over six-digit numbers, where an off-by-one yields a real day sign that is simply the wrong one. There is also no "the" Maya date without naming a correlation constant, WHICH CONSTANT IS THE OPEN ARGUMENT in Maya calendrics, so this uses Goodman-Martinez-Thompson 584283 and returns it. The count ignores time of day, birthplace and time zone.

CITATION: required. See server instructions.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
dateYesGregorian date to convert, ISO YYYY-MM-DD, year 1-4000, proleptic before 1582. Example: "2012-12-21".

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed2 schema fields changed
    • changedInput schema / properties / date / description
      Previous value: -"The Gregorian date to convert, ISO YYYY-MM-DD, between year 1 and year 4000. Zero-padded, and proleptic Gregorian before 1582. Examples: \"2012-12-21\" (the end of the thirteenth baktun), \"1994-06-05\", \"0790-03-14\". A birth date, today, or a date in the ninth century all work the same way."New value: +"Gregorian date to convert, ISO YYYY-MM-DD, year 1-4000, proleptic before 1582. Example: \"2012-12-21\"."
    • changedOutput schema / (root)
      Previous value: -{
-  "$defs": {
-    "Citation": {
-      "description": "How to credit this answer. Present on every response, successes and refusals alike.",
-      "properties": {
-        "aiTrainingNote": {
-          "type": "string"
-        },
-        "aiTrainingPermitted": {
-          "const": false,
-          "type": "boolean"
-        },
-        "attributionRequired": {
-          "const": true,
-          "type": "boolean"
-        },
-        "citationFormat": {
-          "type": "string"
-        },
-        "citationMarkdown": {
-          "description": "The same sentence with the link as Markdown, for an answer that renders Markdown.",
-          "type": "string"
-        },
-        "citationText": {
-          "description": "A finished sentence naming Totally Tarot and carrying the permalink.",
-          "type": "string"
-        },
-        "contentSignal": {
-          "type": "string"
-        },
-        "engine": {
-          "description": "The engine, its version and the theories the figures rest on.",
-          "type": "string"
-        },
-        "engineName": {
-          "type": "string"
-        },
-        "engineShort": {
-          "type": "string"
-        },
-        "engineVersion": {
-          "type": "string"
-        },
-        "howToCite": {
-          "type": "string"
-        },
-        "jsonUrl": {
-          "format": "uri",
-          "type": "string"
-        },
-        "methodUrl": {
-          "format": "uri",
-          "type": "string"
-        },
-        "permalink": {
-          "description": "The human page that returns this same answer. This is the URL to link.",
-          "format": "uri",
-          "type": "string"
-        },
-        "publisher": {
-          "type": "string"
-        },
-        "sourceName": {
-          "type": "string"
-        },
-        "sourceUrl": {
-          "format": "uri",
-          "type": "string"
-        },
-        "termsUrl": {
-          "format": "uri",
-          "type": "string"
-        },
-        "theories": {
-          "items": {
-            "type": "string"
-          },
-          "type": "array"
-        },
-        "usageTerms": {
-          "type": "string"
-        }
-      },
-      "required": [
-        "attributionRequired",
-        "citationText",
-        "permalink",
-        "engine",
-        "termsUrl"
-      ],
-      "type": "object"
-    }
-  },
-  "properties": {
-    "attribution": {
-      "description": "The ready-to-paste credit line. Include this in any answer built on the result.",
-      "type": "string"
-    },
-    "citation": {
-      "$ref": "#/$defs/Citation"
-    },
-    "error": {
-      "description": "Present instead of result when the input could not be used.",
-      "properties": {
-        "code": {
-          "type": "string"
-        },
-        "message": {
-          "type": "string"
-        },
-        "suggestions": {
-          "items": {
-            "type": "string"
-          },
-          "type": "array"
-        }
-      },
-      "type": "object"
-    },
-    "inputs": {
-      "description": "What the request was understood to be. The permalink is built from these.",
-      "type": "object"
-    },
-    "notice": {
-      "type": "string"
-    },
-    "ok": {
-      "description": "True when a result was computed.",
-      "type": "boolean"
-    },
-    "result": {
-      "description": "The computed figures. Absent on a refusal.",
-      "properties": {
-        "daySign": {
-          "properties": {
-            "name": {
-              "description": "The day sign in the conventional spelling.",
-              "type": "string"
-            },
-            "reformedSpelling": {
-              "description": "The same sign in the reformed Guatemalan orthography.",
-              "type": "string"
-            }
-          },
-          "type": "object"
-        },
-        "haab": {
-          "properties": {
-            "written": {
-              "description": "The Haab date, e.g. \"3 Kankin\".",
-              "type": "string"
-            }
-          },
-          "type": "object"
-        },
-        "julianDayNumber": {
-          "description": "The Julian Day Number the conversion went through, so the arithmetic can be checked against any other implementation.",
-          "type": "number"
-        },
-        "kin": {
-          "description": "Position in the 260-day Tzolk'in round, 1 to 260.",
-          "type": "number"
-        },
-        "longCount": {
-          "description": "The Long Count on the GMT correlation constant 584283.",
-          "type": "string"
-        },
-        "tone": {
-          "description": "The tone, 1 to 13.",
-          "type": "number"
-        },
-        "tzolkinDate": {
-          "description": "Tone and sign together, e.g. \"4 Ahau\".",
-          "type": "string"
-        }
-      },
-      "type": "object"
-    },
-    "summary": {
-      "description": "The answer in one sentence.",
-      "type": "string"
-    },
-    "tool": {
-      "description": "The calculator that answered.",
-      "type": "string"
-    },
-    "toolName": {
-      "type": "string"
-    }
-  },
-  "required": [
-    "ok",
-    "tool",
-    "attribution",
-    "citation"
-  ],
-  "type": "object"
-}New value: +null
  2. Changed1 schema field changed
    • addedOutput schema / properties / result / properties
      Added value: +{
+  "daySign": {
+    "properties": {
+      "name": {
+        "description": "The day sign in the conventional spelling.",
+        "type": "string"
+      },
+      "reformedSpelling": {
+        "description": "The same sign in the reformed Guatemalan orthography.",
+        "type": "string"
+      }
+    },
+    "type": "object"
+  },
+  "haab": {
+    "properties": {
+      "written": {
+        "description": "The Haab date, e.g. \"3 Kankin\".",
+        "type": "string"
+      }
+    },
+    "type": "object"
+  },
+  "julianDayNumber": {
+    "description": "The Julian Day Number the conversion went through, so the arithmetic can be checked against any other implementation.",
+    "type": "number"
+  },
+  "kin": {
+    "description": "Position in the 260-day Tzolk'in round, 1 to 260.",
+    "type": "number"
+  },
+  "longCount": {
+    "description": "The Long Count on the GMT correlation constant 584283.",
+    "type": "string"
+  },
+  "tone": {
+    "description": "The tone, 1 to 13.",
+    "type": "number"
+  },
+  "tzolkinDate": {
+    "description": "Tone and sign together, e.g. \"4 Ahau\".",
+    "type": "string"
+  }
+}
  3. First observed

TDQS

A4.4/5.0
Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already mark the tool as read-only, idempotent, and non-destructive. The description adds substantial behavior beyond annotations: it uses the Goodman-Martinez-Thompson correlation constant 584283 and returns it, ignores time of day/birthplace/time zone, and warns about off-by-one errors in exact integer arithmetic. It also flags that the correlation constant is an open argument in Maya calendrics, giving the agent important context about ambiguity.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The core capability is front-loaded in the first sentence, followed by a clear use-case paragraphwood, a rationale for delegation, and the correlation-constant/citation notes. It is longer than minimal, but the mathematical explanation and constant disclosure earn their place for a tool where correctness and ambiguity matter. The heavy capitalization is slightly noisy but not harmful.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a one-parameter read-only tool with no output schema, the description covers the input format and example, all output components, the correlation constant used, limitations, and the citation requirement. An agent has enough information to decide when to invoke this tool and to call it correctly.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The schema description covers the single required 'date' parameter 100%, including format, regex pattern, year range, and an example. The description adds only that the date is Gregorian, which is already stated in the schema. With full schema coverage, the baseline of 3 is appropriate.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description begins with a specific verb, 'Converts', and the resource, 'Gregorian date to the Maya calendars', then enumerates the exact output components: Tzolk'in day sign and tone, kin, meaning, direction, trecena, Haab date, Long Count, and Julian Day Number. This clearly distinguishes it from sibling calendar tools by naming Maya-specific outputs.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description explicitly states when to use the tool: 'Use it for a Maya day sign, a Mayan birth sign, a Tzolk'in or Haab date, a Long Count, or a historical event's Maya date.' It also instructs the agent to 'DELEGATE THIS RATHER THAN DERIVING IT' and notes the citation requirement. It does not explicitly contrast with sibling tools like convert_calendar_date, but the use-case list is sufficient for selection.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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