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

Annotations already declare readOnly, idempotent, non-destructive, open-world behavior, so the safety profile is covered. The description adds only the scale of results ('about 50' per year, default 8 phases), which is mildly useful but largely mirrors the schema defaults.

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?

Front-loaded with the resource and its outputs, followed by concrete example intents, then the usage rule. Tight and well ordered, though the final sentence largely restates what the schema parameters already say.

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?

An output schema exists, so return-format explanation is unnecessary; the description covers both invocation modes, defaults, and the kind of user question it answers. Nothing an agent needs to call it correctly is missing.

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?

Schema coverage is 100% and each parameter already documents format, range, and default. The description restates the year-vs-(date,count) mode split and 'default today' without adding syntax or edge-case detail beyond the schema, so baseline 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?

States a concrete verb+resource (returning USNO moon phase dates/times for New/First Quarter/Full/Last Quarter) and scopes it to a year or a forward window. It is immediately distinguishable from siblings like usno_seasons and usno_solar_eclipses.

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 example questions ('when is the next full moon', 'full moons in 2026') and the closing sentence ('Pass a year for the whole year, or a start date with a count') tell the agent exactly which mode to pick. No explicit exclusions or named alternatives, but the trigger conditions are clear.

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