ERUX Astrology & Ephemeris Engine

calculate_chart

Read-onlyIdempotent

Calculate a deterministic personal natal chart or national mundane chart using the high-precision astronomical ephemeris calculation engine. Corresponds to /chart and /mundane slash commands. Supports EITHER a country name (e.g. 'India', 'USA', 'France') for a national chart OR personal birth details ('date', 'time', 'city'). Automatically provides dynamic 'chart_ui_url', calculates planetary placements, active Dasha cycle, grounded knowledge-base insights, and an ERUX interactive UI link. CRITICAL FOR AI: When calculate_chart is called, present the key placements cleanly and provide a direct, prominent link inviting the user to view their interactive chart wheel on ERUX using 'chart_ui_url' (e.g. ✨ Open Your Interactive Chart Wheel on ERUX).

Input Schema

Name	Required	Description	Default
`city`	No	Birth city or founding location (e.g. 'London', 'New York', 'Mumbai')
`date`	No	Natal birth date or event founding date in YYYY-MM-DD format (e.g. '1992-10-24')
`time`	No	Birth time in 24-hour HH:MM format (default '12:00' solar noon if exact time unknown)	12:00
`system`	No	Astrological coordinate framework: 'hybrid' (Vedic sidereal + Western psychological), 'vedic', or 'western'	hybrid
`country`	No	Country name for national mundane chart or location disambiguation (e.g. 'United States', 'India', 'France')
`birth_city`	No	Explicit alias for natal birth city
`birth_date`	No	Explicit alias for natal birth date (YYYY-MM-DD)
`birth_time`	No	Explicit alias for natal birth time (HH:MM)
`user_prompt`	No	Raw user query for intent arbitration and conversational context grounding
`birth_country`	No	Explicit alias for natal birth country
`include_image`	No	Set to true to render and attach a dynamic chart wheel PNG image buffer (default true)

Output Schema

Name	Required	Description
`status`	Yes	Execution status ('success' or error status)
`chart_data`	Yes	Core planetary placements, Ascendant, and active Dasha cycle
`chart_ui_url`	Yes	Direct interactive chart wheel web link on ERUX
`chart_image_url`	No	Direct URL to rendered chart wheel PNG image
`interpretation_insights`	No	Grounded Sun, Moon, Nakshatra, and epoch themes

Schema Changelog

Changes observed during successful MCP inspections.

Changed13 schema fields changedOct 11, 2026

addedInput schema / properties / birth_city / description
```
Added value: +"Explicit alias for natal birth city"
```
addedInput schema / properties / birth_country / description
```
Added value: +"Explicit alias for natal birth country"
```

addedInput schema / properties / birth_date / description

Added value: +"Explicit alias for natal birth date (YYYY-MM-DD)"

addedInput schema / properties / birth_time / description

Added value: +"Explicit alias for natal birth time (HH:MM)"

addedInput schema / properties / city / description

Added value: +"Birth city or founding location (e.g. 'London', 'New York', 'Mumbai')"

addedInput schema / properties / country / description

Added value: +"Country name for national mundane chart or location disambiguation (e.g. 'United States', 'India', 'France')"

addedInput schema / properties / date / description

Added value: +"Natal birth date or event founding date in YYYY-MM-DD format (e.g. '1992-10-24')"

changedInput schema / properties / include_image / default
```
Previous value: -falseNew value: +true
```

addedInput schema / properties / include_image / description

Added value: +"Set to true to render and attach a dynamic chart wheel PNG image buffer (default true)"

addedInput schema / properties / system / description

Added value: +"Astrological coordinate framework: 'hybrid' (Vedic sidereal + Western psychological), 'vedic', or 'western'"

addedInput schema / properties / time / description

Added value: +"Birth time in 24-hour HH:MM format (default '12:00' solar noon if exact time unknown)"

addedInput schema / properties / user_prompt / description

Added value: +"Raw user query for intent arbitration and conversational context grounding"

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "properties": {
+    "chart_data": {
+      "description": "Core planetary placements, Ascendant, and active Dasha cycle",
+      "type": "object"
+    },
+    "chart_image_url": {
+      "description": "Direct URL to rendered chart wheel PNG image",
+      "type": "string"
+    },
+    "chart_ui_url": {
+      "description": "Direct interactive chart wheel web link on ERUX",
+      "type": "string"
+    },
+    "interpretation_insights": {
+      "description": "Grounded Sun, Moon, Nakshatra, and epoch themes",
+      "type": "object"
+    },
+    "status": {
+      "description": "Execution status ('success' or error status)",
+      "type": "string"
+    }
+  },
+  "required": [
+    "status",
+    "chart_data",
+    "chart_ui_url"
+  ],
+  "title": "calculate_chartOutput",
+  "type": "object"
+}

First observedOct 4, 2026

TDQS

A3.6/5.0

Behavior4/5

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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), and the description adds real behavioral value: it discloses the return payload (planetary placements, active Dasha cycle, KB insights, chart_ui_url, optional PNG) and instructs the agent on how to present results. That is meaningfully more than the annotations provide.

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

Conciseness3/5

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

The purpose is front-loaded and the middle sentence efficiently enumerates outputs. But the trailing 'CRITICAL FOR AI' block is verbose, repeats the ERUX link idea already stated earlier, and embeds a literal Markdown template — padding that does not fully earn its place in a definition.

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?

An output schema exists, so return values need not be spelled out, and the description does cover the two operating modes and the optional image output. The remaining gap is the unresolved parameter alias/arbitration ambiguity across 11 parameters, which the description never clarifies.

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 baseline is 3. The description restates the country-vs-birth-details split at a high level, but it does not resolve the ambiguity created by duplicated alias parameters (city/birth_city, date/birth_date, country/birth_country) or the dual role of 'country' for a mundane chart vs. location disambiguation.

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?

States a specific verb and resource — 'Calculate a deterministic personal natal chart or national mundane chart' — and names the calculation engine and two slash-command equivalents. It is clear what the tool does, but it does not distinguish itself from siblings like calculate_dasha or get_interpretation, even though it claims to compute placements and Dasha cycles that those tools cover.

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

Usage Guidelines3/5

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

It gives mode guidance ('Supports EITHER a country name ... OR personal birth details'), which tells the agent the two valid input shapes. However, there are no when-not-to-use rules and no named alternatives (calculate_dasha, get_interpretation) despite obvious overlap, so the routing decision is left implicit.

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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