Usno Astronomy

Usno Eclipse Circumstances

usno_eclipse_circumstances

Read-onlyIdempotent

Local circumstances of a solar eclipse at a given latitude/longitude on a given date — whether the Sun is totally, annularly or partially eclipsed there, the magnitude and obscuration (percentage of the Sun covered), the duration, and the UT time, Sun altitude and azimuth of each contact (eclipse begins, totality begins/ends, maximum eclipse, eclipse ends, or sunrise/sunset if the eclipse is in progress then). Answers "what time does the August 12 2026 eclipse start in Madrid", "how much of the Sun will be covered in Denver", "will the eclipse be total where I am". Needs coordinates: resolve a place name to lat/lon first. Find the eclipse date with usno_solar_eclipses.

Example tool call

This call uses example arguments supplied in the tool’s input schema.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "lat": 40.42,
      "lon": -3.7,
      "date": "2026-08-12"
    },
    "name": "usno_eclipse_circumstances"
  }
}

Input Schema

Name	Required	Description
`lat`	Yes	Latitude in decimal degrees, north positive, e.g. 40.42 for Madrid.
`lon`	Yes	Longitude in decimal degrees, east positive, e.g. -3.70 for Madrid.
`date`	Yes	Date of the eclipse as YYYY-MM-DD, e.g. "2026-08-12". Must be a solar eclipse date from usno_solar_eclipses.
`height`	No	Observer height in metres above sea level. Default 0.

Output Schema

Name	Required	Description	Default
`event`	No
`found`	Yes
`source`	Yes
`contacts`	No
`duration`	No
`magnitude`	No
`time_note`	Yes
`description`	No
`obscuration_pct`	No

Schema Changelog

Changes observed during successful MCP inspections.

First observedSep 11, 2026

TDQS

A4.6/5.0

Behavior4/5

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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is covered. The description adds meaningful domain context by defining what 'circumstances' means (which contacts, magnitude, obscuration, and sunrise/sunset-in-progress handling), which the annotations cannot convey. It stops short of any operational caveats (rate limits, precision/edge cases near poles), so it isn't a 5.

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 core purpose is front-loaded in the first sentence, and example queries make intent concrete. However, the long enumeration of contact types and output fields partially duplicates what the output schema already provides, so a little could be trimmed.

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?

Given an output schema exists, the description needn't explain return values, yet it does so in domain terms. Combined with the coordinate prerequisite and the sibling reference for dates, an agent has everything needed to invoke the tool correctly.

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, but the description goes beyond the schema by tying lat/lon to an upstream geocoding step and tying date to the usno_solar_eclipses source. It doesn't add coordinate-format nuance beyond what the schema examples already show.

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 names a specific verb+resource ('Local circumstances of a solar eclipse at a given latitude/longitude on a given date') and enumerates the exact outputs (totality/annularity/partial, magnitude, obscuration, duration, contact UT times). It clearly distinguishes itself from the sibling usno_solar_eclipses by framing that tool as the source for finding eclipse dates.

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

Usage Guidelines5/5

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

Gives concrete example questions the tool answers ('what time does the August 12 2026 eclipse start in Madrid'), states the prerequisite explicitly ('Needs coordinates: resolve a place name to lat/lon first'), and routes to the sibling needed to obtain the date ('Find the eclipse date with usno_solar_eclipses'). When-to-use and dependencies are both spelled out.

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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