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Saju / BaZi natal chart

saju_chart
Read-onlyIdempotent

Generates a Four Pillars (BaZi) chart from birth data, covering stems, branches, Ten Gods, hidden stems, five-element ratios, Spirit Stars, and Twelve Life Stages. Use it to show your BaZi chart.

Instructions

Four Pillars (四柱八字) natal chart: year/month/day/hour stems and branches, Ten Gods (十神), hidden stems, five-element ratios, Spirit Stars (神殺) and Twelve Life Stages (十二運星) per pillar. The foundation other tools build on. Use for 'show my saju / bazi chart', '내 사주 봐줘'.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
locNo24Plus world-city ID for births outside Korea.
sexNoSex at birth; sets the direction of the 10-year luck cycles. Required unless legacy 'gender' is given.
nameNoOptional display name.
birthYesLocal birth date and time. ISO 8601 'YYYY-MM-DDTHH:mm' (e.g. 1990-01-15T10:30) or legacy 12 digits 'YYYYMMDDHHmm'. Use 12:30 when the time is unknown and set time_unknown.
genderNoLegacy form of sex: 0 female, 1 male.
option1NoLegacy form of rat_hour_rule (1 = early).
option2NoLegacy form of year_boundary (-1 = winter_solstice).
calendarNoCalendar of the birth date. Default solar.
is_lunarNoLegacy form of calendar=lunar.
timezoneNoIANA time zone of the birthplace. Asia/Seoul is supported directly; for births elsewhere pass 'loc'.
is_leap_yearNoLegacy form of lunar_leap_month.
time_unknownNoBirth time unknown; the hour pillar is marked as estimated.
rat_hour_ruleNoRat-hour (子時) rule: 'late' 야자시 (default) or 'early' 조자시.
year_boundaryNoYear pillar boundary: 'lichun' 입춘 (default) or 'winter_solstice' 동지.
lunar_leap_monthNoLunar leap month (윤달). Only with calendar=lunar.

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault
dataYes
toolYes
basisNoChart basis text ([기본정보]): pillars, calendar/season basis, luck-cycle start.
linksYes
engineYes
contractYes
disclaimerYes
input_echoYes

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed30 schema fields changedv1.0.1
    • addedInput schema / $schema
      Added value: +"http://json-schema.org/draft-07/schema#"
    • changedInput schema / properties / birth / description
      Previous value: -"Birth date & time, 12 digits YYYYMMDDHHMM (e.g. 199001151030). Use 1230 for unknown time."New value: +"Local birth date and time. ISO 8601 'YYYY-MM-DDTHH:mm' (e.g. 1990-01-15T10:30) or legacy 12 digits 'YYYYMMDDHHmm'. Use 12:30 when the time is unknown and set time_unknown."
    • addedInput schema / properties / calendar
      Added value: +{
      +  "description": "Calendar of the birth date. Default solar.",
      +  "enum": [
      +    "solar",
      +    "lunar"
      +  ],
      +  "type": "string"
      +}
    • addedInput schema / properties / gender / anyOf
      Added value: +[
      +  {
      +    "const": 0,
      +    "type": "number"
      +  },
      +  {
      +    "const": 1,
      +    "type": "number"
      +  }
      +]
    • changedInput schema / properties / gender / description
      Previous value: -"Gender — 0: female, 1: male (CAFE convention)."New value: +"Legacy form of sex: 0 female, 1 male."
    • removedInput schema / properties / gender / enum
      Removed value: -[
      -  0,
      -  1
      -]
    • removedInput schema / properties / gender / type
      Removed value: -"integer"
    • changedInput schema / properties / is_leap_year / description
      Previous value: -"Optional. true if the lunar birth month is a leap month (윤달). Only meaningful with is_lunar=true."New value: +"Legacy form of lunar_leap_month."
    • changedInput schema / properties / is_lunar / description
      Previous value: -"Optional. true if the birth date is a lunar-calendar date (default false = solar)."New value: +"Legacy form of calendar=lunar."
    • changedInput schema / properties / loc / description
      Previous value: -"Optional birthplace region ID for overseas births (24Plus world-city ID). Omit for Korea."New value: +"24Plus world-city ID for births outside Korea."
    • addedInput schema / properties / loc / maximum
      Added value: +9007199254740991
    • addedInput schema / properties / loc / minimum
      Added value: +-9007199254740991
    • addedInput schema / properties / lunar_leap_month
      Added value: +{
      +  "description": "Lunar leap month (윤달). Only with calendar=lunar.",
      +  "type": "boolean"
      +}
    • changedInput schema / properties / name / description
      Previous value: -"Optional name. Affects some engine outputs; omit to use the default."New value: +"Optional display name."
    • addedInput schema / properties / name / maxLength
      Added value: +40
    • addedInput schema / properties / option1 / anyOf
      Added value: +[
      +  {
      +    "const": 0,
      +    "type": "number"
      +  },
      +  {
      +    "const": 1,
      +    "type": "number"
      +  }
      +]
    • changedInput schema / properties / option1 / description
      Previous value: -"Optional Rat-hour (자시) rule — 0: Ya-jasi/야자시 (default), 1: Jo-jasi/조자시."New value: +"Legacy form of rat_hour_rule (1 = early)."
    • removedInput schema / properties / option1 / enum
      Removed value: -[
      -  0,
      -  1
      -]
    • removedInput schema / properties / option1 / type
      Removed value: -"integer"
    • addedInput schema / properties / option2 / anyOf
      Added value: +[
      +  {
      +    "const": 0,
      +    "type": "number"
      +  },
      +  {
      +    "const": -1,
      +    "type": "number"
      +  }
      +]
    • changedInput schema / properties / option2 / description
      Previous value: -"Optional year-pillar season basis — 0: Ipchun/입춘 (default, standard practice), -1: Dongji/동지."New value: +"Legacy form of year_boundary (-1 = winter_solstice)."
    • removedInput schema / properties / option2 / enum
      Removed value: -[
      -  0,
      -  -1
      -]
    • removedInput schema / properties / option2 / type
      Removed value: -"integer"
    • addedInput schema / properties / rat_hour_rule
      Added value: +{
      +  "description": "Rat-hour (子時) rule: 'late' 야자시 (default) or 'early' 조자시.",
      +  "enum": [
      +    "late",
      +    "early"
      +  ],
      +  "type": "string"
      +}
    • addedInput schema / properties / sex
      Added value: +{
      +  "description": "Sex at birth; sets the direction of the 10-year luck cycles. Required unless legacy 'gender' is given.",
      +  "enum": [
      +    "female",
      +    "male"
      +  ],
      +  "type": "string"
      +}
    • changedInput schema / properties / time_unknown / description
      Previous value: -"Optional. true if the birth time is unknown — the chart header marks the hour pillar as estimated. Pair with HHMM=1230."New value: +"Birth time unknown; the hour pillar is marked as estimated."
    • addedInput schema / properties / timezone
      Added value: +{
      +  "description": "IANA time zone of the birthplace. Asia/Seoul is supported directly; for births elsewhere pass 'loc'.",
      +  "type": "string"
      +}
    • addedInput schema / properties / year_boundary
      Added value: +{
      +  "description": "Year pillar boundary: 'lichun' 입춘 (default) or 'winter_solstice' 동지.",
      +  "enum": [
      +    "lichun",
      +    "winter_solstice"
      +  ],
      +  "type": "string"
      +}
    • changedInput schema / required
      Previous value: -[
      -  "birth",
      -  "gender"
      -]New value: +[
      +  "birth"
      +]
    • changedOutput schema / (root)
      Previous value: -nullNew value: +{
      +  "$schema": "http://json-schema.org/draft-07/schema#",
      +  "additionalProperties": false,
      +  "properties": {
      +    "basis": {
      +      "description": "Chart basis text ([기본정보]): pillars, calendar/season basis, luck-cycle start.",
      +      "type": "string"
      +    },
      +    "contract": {
      +      "type": "string"
      +    },
      +    "data": {
      +      "additionalProperties": false,
      +      "properties": {
      +        "label": {
      +          "type": "string"
      +        },
      +        "panel_count": {
      +          "type": "number"
      +        },
      +        "panels": {}
      +      },
      +      "required": [
      +        "panels"
      +      ],
      +      "type": "object"
      +    },
      +    "disclaimer": {
      +      "type": "string"
      +    },
      +    "engine": {
      +      "const": "cafe",
      +      "type": "string"
      +    },
      +    "input_echo": {
      +      "additionalProperties": false,
      +      "properties": {
      +        "birth": {
      +          "type": "string"
      +        },
      +        "calendar": {
      +          "type": "string"
      +        },
      +        "sex": {
      +          "type": "string"
      +        },
      +        "timezone": {
      +          "type": "string"
      +        }
      +      },
      +      "required": [
      +        "birth",
      +        "calendar",
      +        "sex",
      +        "timezone"
      +      ],
      +      "type": "object"
      +    },
      +    "links": {
      +      "additionalProperties": false,
      +      "properties": {
      +        "web": {
      +          "type": "string"
      +        }
      +      },
      +      "required": [
      +        "web"
      +      ],
      +      "type": "object"
      +    },
      +    "tool": {
      +      "type": "string"
      +    }
      +  },
      +  "required": [
      +    "engine",
      +    "contract",
      +    "tool",
      +    "input_echo",
      +    "data",
      +    "links",
      +    "disclaimer"
      +  ],
      +  "type": "object"
      +}
  2. First observedv0.1.0

TDQS

A3.8/5.0
Behavior3/5

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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is well covered. The description adds useful context about chart content and foundational role, but it does not disclose operational behaviors such as how unknown birth time is handled, timezone assumptions, or how lunar/legacy parameters affect computation. With annotations present, this is an acceptable but not rich disclosure.

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

Conciseness5/5

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

The description is three sentences with no filler. The first sentence front-loads the chart contents, the second establishes its role relative to other tools, and the third gives concrete usage examples. Every sentence earns its place and the structure is easy to scan.

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

Completeness4/5

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

Given the tool's complexity (15 parameters) but the presence of a rich input schema and an output schema, the description does not need to restate parameter details or return values. It provides the key contextual signals an agent needs for selection: what the chart contains, that it is foundational, and example user phrasings. A small gap is the lack of any hint about when not to use this tool or which sibling addresses more specialized chart-reading tasks.

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?

Schema description coverage is 100%, so the schema already documents every parameter. The description adds no parameter-level meaning beyond what the schema provides. Per the baseline rule, a 3 is appropriate when the schema carries the full semantic burden.

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

Purpose4/5

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

The description clearly explains that the tool produces a Four Pillars natal chart and enumerates the chart components (stems/branches, Ten Gods, hidden stems, five-element ratios, Spirit Stars, Twelve Life Stages). It does not use a direct verb like 'calculate' or 'generate', and it does not explicitly contrast itself with any sibling tool, though labeling it 'the foundation other tools build on' provides some positional clarity.

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 gives explicit user-intent examples ('show my saju / bazi chart', '내 사주 봐줘'), which tells an agent when to invoke this tool. It also states that it is the foundation for other tools, implying it is the right first step for chart-related requests. It does not enumerate exclusions or alternative tool conditions, so it stops short of a 5.

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