AgentTime — True Time & Astronomy

get_moon_phases

Get upcoming moon phases (New Moon, First Quarter, Full Moon, Last Quarter) and current moon illumination percentage from the US Naval Observatory.

Tool call template

This tool declares no required parameters. Add optional parameters from the input schema as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {},
    "name": "get_moon_phases"
  }
}

Input Schema

Name	Required	Description	Default
`date`	No	Start date in YYYY-MM-DD format (default: today)
`count`	No	Number of phases to return (default: 4, max: 99)

Schema Changelog

Changes observed during successful MCP inspections.

First observedMay 29, 2026

TDQS

A4/5.0

Behavior3/5

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

No annotations are provided, so the description carries the burden of disclosure. It describes the tool as a read-like operation ('Get'), but does not explicitly state it is non-destructive or mention potential side effects. The absence of explicit behavioral traits beyond the obvious limits transparency.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single 24-word sentence that is front-loaded with the primary action and key output details. Every word contributes meaning; no redundancy or fluff.

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

Completeness4/5

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

Given the absence of an output schema, the description adequately explains the return value (upcoming phases and current illumination). However, it could be more explicit about ordering (chronological) and the precise meaning of 'current illumination' (e.g., for today).

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% with descriptions for both parameters. The description adds value by explaining the output (list of upcoming phases and current illumination) and the source, providing context beyond the schema definitions.

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 clearly states the tool retrieves upcoming moon phases (listing four specific types) and current moon illumination percentage from a specific authoritative source (US Naval Observatory). It distinguishes itself from siblings like get_astronomy (broader) and get_current_time (time-only).

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?

The description implies usage for moon phase data but does not provide explicit guidance on when to use this tool over alternatives like get_astronomy. No when-not or exclusion criteria are mentioned.

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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