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

Annotations already establish this as a safe, read-only, open-world call, so the description's extra value is its disclosure of a 2-credit cost and plan-tier limitations (custom dates, azimuth, and distance gated behind paid plans). Those are behaviors the agent cannot infer from annotations or schema, though unit/return-format details are left to the output schema.

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 key capability and the cost notice are front-loaded and there is little waste. The only flaw is the redundant 'Moon Position: Moon Position calculates...' echo of the title before the actual content.

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?

With annotations covering safety, a full output schema, and complete parameter descriptions, the remaining burden on the description is pricing and plan limits — both covered. The only gap is that it doesn't clarify whether altitude is returned in degrees or how the coordinate timezone default interacts with the optional timezone param.

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%, so the baseline is 3, but the description adds meaning the schema does not: the 'date' parameter is effectively paywalled and azumuth/distance outputs require a paid plan. That tier gating is real semantic context beyond the property descriptions.

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 names a specific verb and resource — calculating the moon's altitude for a latitude/longitude pair — which is concrete and distinguishable from celestial siblings like MoonPhases and MoonriseMoonset by focusing on elevation at a point. It never explicitly contrasts those siblings, so the differentiation is implied rather than stated.

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?

Usage is only implied: the agent learns it needs coordinates, and that optional time refines the result. There is no explicit when-to-use/when-not guidance versus MoonriseMoonset or MoonPhases, though the tier note ('paid plans add custom dates, azimuth, and distance') does give actionable context about what is available.

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