APIVerve

Birth Chart

BirthChart

Read-only

Birth Chart: Birth Chart calculates a tropical natal chart from a birth date, time and location. It returns the sun, moon and rising signs, the ascendant and midheaven, and each planet's sign, degree and retrograde flag. Paid plans add the 12 house cusps, each planet's house, the major aspects and the element and modality balance. (Cost: 5 credits)

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "date": "<date>",
      "time": "<time>",
      "lat": "<lat>",
      "lon": "<lon>"
    },
    "name": "BirthChart"
  }
}

Input Schema

Name	Required	Description	Default
`lat`	Yes	The latitude of the birthplace
`lon`	Yes	The longitude of the birthplace (east positive)
`date`	Yes	The birth date (YYYY-MM-DD or MM-DD-YYYY), between 1700 and 2200
`time`	Yes	The local birth time in 24-hour HH:mm format
`timezone`	No	An IANA timezone name (America/New_York) or a UTC offset (+05:30). Looked up from the coordinates when omitted
`houseSystem`	No	The house system to use	placidus

Output Schema

Name	Required	Description
`data`	No
`error`	No	Error message, null on success
`status`	No	"ok" on success

Schema Changelog

Changes observed during successful MCP inspections.

First observedNov 7, 2026

TDQS

A3.8/5.0

Behavior4/5

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

The annotations already establish that this is a read-only, open-world, non-destructive operation, so the description does not need to restate safety. It adds meaningful behavior beyond annotations by disclosing the 5-credit cost and plan-gated output tiers: free results include signs, angles, and planetary details, while paid plans add houses, aspects, and balance data.

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 description is front-loaded and efficiently covers purpose, outputs, plan tiers, and cost. The opening 'Birth Chart: Birth Chart' repeats the tool name and title unnecessarily, but the remaining sentences earn their place.

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?

The tool has a rich schema, an output schema, and annotations, and the description supplies the missing behavioral context: credit cost and paid-plan output differences. It also gives enough return-value context for an agent to understand the tool's scope despite the output schema being present. No critical calling information is missing for this read-only calculation tool.

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 input schema already defines date, time, latitude, longitude, timezone, and houseSystem. The description mentions birth date, time, and location but adds no detail about timezone lookup, house-system defaults, or format constraints beyond the schema. The baseline score of 3 is appropriate when the schema carries parameter semantics.

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 states a specific verb and resource: it calculates a tropical natal chart from birth date, time, and location. The natal-chart framing and birth-data inputs distinguish it from nearby astronomy/astrology siblings such as PlanetPositions or Horoscope. It also previews the returned signs, angles, and planetary details, so an agent can tell what the tool produces.

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

Usage Guidelines2/5

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

There is no explicit when-to-use or when-not guidance, and no alternatives are named. The description implies usage through its purpose, but with many astrology-related siblings an agent is left to infer when BirthChart is preferable to PlanetPositions, Horoscope, or SunPosition.

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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