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

Annotations already declare safe readonly behavior. The description adds value by noting the output includes exact UTC timestamps, approximately 50 phases per year, and cites the authoritative US Naval Observatory source. This provides useful context beyond the annotations, though it does not mention potential performance or rate limits.

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

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

The description consists of two short, information-dense sentences. The first conveys the core functionality and output specifics; the second adds credibility and source. Every word earns its place, and there is no verbosity or redundancy.

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

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

Given the tool's simplicity (one optional parameter, output schema exists, no nested objects), the description provides sufficient context: what phases are returned, timestamps, approximate count, and data provenance. It covers the essential details for correct invocation without needing additional explanation.

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

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

The input schema has 100% coverage for the single 'year' parameter (with description). The description does not add new parameter semantics beyond restating 'for a year'. Since the schema already documents the parameter well, a baseline score of 3 is appropriate.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states it retrieves all moon phase dates for a year, listing the four phases (New Moon, First Quarter, Full Moon, Last Quarter) with exact UTC timestamps. This specific verb+resource makes the purpose unmistakable and distinguishes it from other astronomical tools like seasons or sun/moon data.

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

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

The description implies usage for obtaining moon phase dates but provides no explicit guidance on when to use or not use this tool versus siblings like usno.astronomy.seasons or usno.astronomy.sun_moon. The context is clear enough for a simple query, so it meets the minimal bar but lacks comparative direction.

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