explore_moon_phase

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

Annotations already declare read-only, idempotent, and non-destructive, but the description adds credit cost (3 credits with breakdown), real-time update behavior, and the fallback from an interactive dial to a text summary. These operational details go beyond what the annotations alone provide.

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 is front-loaded with the core purpose and uses a bulleted list to keep details scannable. Every element—credit cost, sibling differentiation, fallback behavior—adds value, and there is no filler.

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 there is no output schema, the bullet list reasonably describes the returned dial contents. However, the credit cost mentions 'aspects' but the output list doesn't explicitly include an aspects element, and the 'text summary' fallback is underspecified, keeping it from a perfect score.

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 all four parameters, with each parameter already described in detail. The tool description adds no parameter-specific meaning beyond the schema, so the 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 opens with a specific verb ('Generate an interactive Moon Phase dial') and names the exact resource: current lunar illumination, phase name, zodiac sign, and void-of-course status. It clearly distinguishes this from the sibling ephemeris_moon_phase by positioning it as the rich interactive variant.

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?

It explicitly says 'Use this instead of ephemeris_moon_phase for a rich, interactive lunar phase experience in MCP Apps-capable hosts (Claude Desktop)' and notes the fallback behavior in other hosts. This gives the agent a clear decision rule for choosing this tool over the alternative.

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