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astronomy-mcp-server

by io.github.cyanheads

astronomy-mcp-server: get rise/set times

astronomy_get_rise_set
Read-onlyIdempotent

Compute rise, set, and culmination (transit) times for a body at an observer location, plus the maximum altitude at culmination. For the Sun, also returns the three twilight pairs (civil −6°, nautical −12°, astronomical −18°) so a single call answers "when does the sun set and when is it truly dark." Searches forward from start (default today) and returns the next count cycles (default 1). When the body is already above the horizon at start, the first cycle is the interval in progress: its set is the imminent one and its rise is null, since that rise precedes the search — so a set is never reported earlier than the rise beside it. Circumpolar or never-rises situations are reported as null rise/set fields with an explanatory note rather than an error — the fact is the answer. Default elevation is 0 m; pass an IANA timezone for observer-local times. This server does not geocode — resolve coordinates upstream first.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
bodyYesThe body to compute rise/set for. Twilight is included only when this is "sun".
countNoNumber of forward rise/set cycles to return. Default 1, max 31.
startNoSearch start as an ISO 8601 UTC string, e.g. "2024-06-21T00:00:00Z". Defaults to now. A value with no zone designator is read as UTC, not the local zone of the server process.
latitudeYesObserver latitude in decimal degrees, north positive.
timezoneNoIANA timezone for localized output, e.g. "America/Los_Angeles". When omitted, output is UTC-only.
elevationNoObserver elevation in meters above sea level. Default 0.
longitudeYesObserver longitude in decimal degrees, east positive.

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault
bodyNoThe body these rise/set cycles are for, echoed from the request.
errorNoPresent when the call failed. Absent on success.
eventsNoOne entry per rise/set/transit cycle, searching forward from the start time.
totalCountNoNumber of rise/set cycles returned.

TDQS

A4.6/5.0
Behavior5/5

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

With annotations already declaring readOnlyHint=true and idempotentHint=true, the description adds valuable behavioral nuance beyond those hints: it explains the null-rise behavior when the body is already above the horizon, and how circumpolar/never-rises cases return null fields with explanatory notes instead of errors. This is exactly the kind of edge-case transparency that informs correct invocation.

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 long but each sentence earns its place: the core purpose is front-loaded, then edge cases and prerequisites follow logically. It could be tightened marginally, but for a tool with 7 parameters and several non-obvious behaviors, the detail is justified and well-structured.

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?

An output schema exists, so return structure is covered elsewhere. The description covers all operational aspects necessary for correct use: search direction, interval-in-progress logic, null handling for polar cases, default elevation, timezone handling, and the explicit geocoding limitation. Nothing essential is missing.

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

Parameters4/5

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

Schema coverage is 100%, so the baseline is 3. The description nevertheless adds semantic value: it clarifies what 'count' cycles means, explains the default start as 'today' (schema says 'now' – a minor imprecision), and notes the timezone effect on output. It also ties the twilight parameter to the Sun. This goes beyond simple schema restatement, warranting a 4.

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 opens with a precise verb+resource statement: 'Compute rise, set, and culmination (transit) times for a body at an observer location, plus the maximum altitude at culmination.' This clearly distinguishes it from siblings like astronomy_get_ephemeris or astronomy_get_sky_position. The Sun-specific twilight addition further sharpens its identity.

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?

It gives explicit context on search direction ('Searches forward from `start`'), defaults, and the observer-ground requirement ('This server does not geocode — resolve coordinates upstream first'). However, it does not name alternative tools for contrasting use cases, 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.

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TDQS

A4.6/5.0
Disambiguation5/5

Each tool targets a clearly distinct aspect of astronomy: event lookup, ephemeris for small bodies, moon phase, rise/set times, satellite passes, sky position for bodies/stars, and a visible-objects summary. Even overlapping capabilities (e.g., get_sky_position vs. get_ephemeris) are separated by scope (single instant vs. time series, major bodies vs. small bodies). No ambiguity in choosing between tools.

Naming Consistency5/5

All tool names follow a consistent pattern: 'astronomy_' prefix + descriptive verb ('find', 'get', 'list') + object. The verbs are homogeneous (mostly 'get_', plus 'find_events' and 'list_visible'), and the snake_case style is uniform. Predictable and easy to navigate.

Tool Count5/5

Seven tools is a well-scoped number for an astronomy server. Each tool covers a distinct major query type, and none feel redundant or unnecessary. This is within the ideal 3–15 range and feels neither too thin nor too heavy.

Completeness5/5

The tool set covers the full range of common astronomy asks: positions, phases, events, rise/set, satellite passes, and a 'what's up' overview. Small-body ephemerides fill the gap for non-major objects. There are no obvious dead ends; an agent can answer most user questions with these tools alone.

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