Usno Astronomy

Usno Solar Eclipses

usno_solar_eclipses

Read-onlyIdempotent

When is the next solar eclipse — the list of solar eclipses in a year from the US Naval Observatory, each with its date and type (total, annular, partial, hybrid). With no arguments it returns the NEXT solar eclipse after today plus the rest of the current and following year, so "when is the next solar eclipse", "solar eclipses in 2027", "is there a total eclipse this year" are all one call. For where an eclipse is visible and what time it starts at a given place, follow with usno_eclipse_circumstances. Lunar eclipses are not published by this API.

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": {},
    "name": "usno_solar_eclipses"
  }
}

Input Schema

Name	Required	Description	Default
`year`	No	Four-digit year, 1800-2050. Omit for the next eclipse after today (current year and the next).

Output Schema

Name	Required	Description	Default
`source`	Yes
`eclipses`	Yes
`time_note`	Yes
`next_eclipse`	No
`years_covered`	Yes

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 cover the safety profile (readOnly, idempotent, openWorld), so the bar is lower, and the description adds the important default-behavior contract for an optional-parameter tool. It also discloses a scope boundary (lunar eclipses not published). It does not discuss result limits or ordering beyond the default case, so not a full 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?

Front-loaded with the user question, then default behavior, then the follow-on tool and the exclusion. Every sentence carries information, though the opening sentence is slightly convoluted with its em-dash construction.

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 explanation is unnecessary, and the remaining agent needs — default behavior with no arguments, the alternative tool for location/time, and the lunar-eclipse exclusion — are all present. Nothing required to invoke this correctly 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% and the single parameter is fully documented there, so baseline is 3. The description adds value beyond the schema by stating the semantic consequence of omission (next eclipse after today, spanning the current and following year) and grounding the parameter in worked examples like 'solar eclipses in 2027'.

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?

Specific verb+resource: it lists solar eclipses for a year, and explicitly names what each entry contains (date, type, with the total/annular/partial/hybrid enum spelled out). It is clearly distinguishable from usno_moon_phases, usno_seasons, and usno_eclipse_circumstances.

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 the no-argument default explicitly ('returns the NEXT solar eclipse after today plus the rest of the current and following year') and maps three concrete natural-language questions onto this single call. It routes onward to usno_eclipse_circumstances for location/timing and excludes lunar eclipses, which is a genuine when-not-to-use signal.

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

Try in Browser

One endpoint for every MCP toolRayrun runs every MCP server behind one URL and holds the credentials. Each call is decided per client, tool, and argument, then recorded.ray.runAd

Glama MCP Gateway

Add one secure layer between your agents and this server.