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astroway-mcp

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by astroway

Moon Phase (SVG)

astroway_render_moon_phase
Read-onlyIdempotent

Render the moon disk with its illuminated fraction at any given moment, returning an SVG plus illumination metrics for charts and reports.

Instructions

Render the moon disk with its illuminated fraction at the given moment. Returns SVG plus illumination metrics.

[Group: Visualization] [Endpoint: POST /v1/render/moon-phase] [Cost: 10 credits (Tier 1)]

Input Schema

NameRequiredDescriptionDefault
bodyYesBirth data for a single natal chart. Required: date (YYYY-MM-DD), time (HH:mm:ss), latitude and longitude in decimal degrees. The short forms lat, lon, lng and tz are rejected with 400 INVALID_FIELD; pass the full names. timezoneOffset is hours from UTC and defaults to 0, meaning UTC; send timezone instead (an IANA name such as Europe/Kyiv, or auto) and the offset for that date is worked out, summer time included. city is a display label only: nothing here geocodes it, so it never stands in for coordinates. houseSystem is a single Swiss Ephemeris letter, P by default; a name such as "Placidus" is refused, and the case matters because I and i are two different Sunshine systems.

Output Schema

NameRequiredDescriptionDefault
svgNo
phaseNo
waxingNo
elongationDegNo
illuminationFractionNo

Schema Changelog

Changes observed during successful MCP inspections.

  1. Addedv1.6.0

TDQS

B3.4/5.0
Behavior3/5

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

Annotations already declare readOnly/idempotent/non-destructive, so safety is covered. The description adds genuinely useful cost context ('10 credits (Tier 1)') and endpoint, but it says 'Returns SVG' without noting that options.format defaults to 'json', so the default payload shape is left ambiguous.

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?

Two front-loaded sentences do the real work, followed by short bracketed metadata lines for group, endpoint, and cost. Nothing is padded or redundant, though the metadata block is boilerplate rather than explanatory.

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

Completeness3/5

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

An output schema exists and annotations cover safety, so those do not need restating. However the request body is a full natal-chart schema (ayanamsa, houseSystem, zodiacType) for what is a simple moon-disk render, and the description gives no hint about which of those fields actually matter here — a real gap for correct invocation.

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% and the body/options schema is heavily annotated (timezone, ayanamsa, theme css variables, houseSystem letters all documented inline), so the schema carries the load. The description only contributes the vague phrase 'at the given moment' — no added meaning about date/time/coordinates or the size/theme/format options.

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 — 'Render the moon disk with its illuminated fraction at the given moment' — and names the artifact returned (SVG plus illumination metrics). It is clearly distinguishable from the astroway_render_wheel_* / bi_wheel family by name, but it never contrasts itself with the data-only sibling astroway_calendar_moon_phase, which is the most likely confusion.

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?

Usage is only implied: the reader infers 'use this when you want a picture rather than numbers', but no sentence says when to prefer it over astroway_calendar_moon_phase or astroway_stream_lunar_phase. There are no exclusions, prerequisites, or alternative routing stated.

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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