Usno Astronomy

Usno Seasons

usno_seasons

Read-onlyIdempotent

The seasons for a year from the US Naval Observatory: the UT date and time of the March and September equinoxes, the June and December solstices, and Earth's perihelion and aphelion. Answers "when is the summer solstice", "what date is the autumn equinox in 2027", "first day of spring", "when is Earth closest to the Sun". Northern-hemisphere season names are attached; the southern hemisphere is the opposite.

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": {
      "year": 2026
    },
    "name": "usno_seasons"
  }
}

Input Schema

Name	Required	Description	Default
`year`	No	Four-digit year, 1800-2050. Default: current year.

Output Schema

Name	Required	Description	Default
`year`	Yes
`events`	Yes
`source`	Yes
`time_note`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

First observedSep 11, 2026

TDQS

A4.2/5.0

Behavior4/5

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

Annotations already cover read-only, idempotent, open-world safety. The description adds genuinely new behavioral context: values are UT date and time (not local), and northern-hemisphere season names are attached with the southern hemisphere being the opposite. That naming/timezone convention is exactly the kind of detail an agent cannot infer from the annotations.

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 payload (events covered) is front-loaded and every clause carries information. The cluster of example phrasings is slightly repetitive but functions as recognizable search-intent anchors rather than filler.

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-value structure need not be restated. Combined with the annotations covering the safety profile and the description covering event scope, hemisphere convention, and time standard, an agent has everything needed to call and interpret this correctly.

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 single 'year' parameter is fully documented there, including the 1800-2050 range and current-year default. The description only says 'for a year' and adds no format or bound information beyond the schema, so baseline 3 applies.

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 resource (USNO seasons) and enumerates exactly what is returned: March/September equinoxes, June/December solstices, and perihelion/aphelion. This is precise enough to separate it from siblings like usno_moon_phases and usno_solar_eclipses without opening any schema.

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?

The quoted natural-language queries ('when is the summer solstice', 'first day of spring', 'when is Earth closest to the Sun') clearly signal the request patterns this tool serves. However it never states when NOT to use it or names a sibling tool for adjacent needs, so it stops short of full routing guidance.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

All Usno Astronomy tools Inspect

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