ephemeris_moon_phase

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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint false, covering the basic safety profile. The description adds valuable behavioral context such as credit cost (2 credits), separate metering for phase and void-of-course, and the live moon phase default when no datetime is provided.

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 well-organized: a concise main statement, followed by structured sections for answers/non-answers, alternatives, credit cost, and default behavior. Every sentence earns its place, contributing critical information without unnecessary verbosity.

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?

The description covers the return values (phase name, illumination, sign/degree, void-of-course), usage boundaries, credit cost, and default behavior. Even without an output schema, it gives the agent enough context to understand what to expect and how to invoke the tool correctly.

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?

All parameters are fully described in the schema (100% coverage), so the baseline is 3. The description adds meaningful semantics by clarifying that omitting the datetime parameter returns the current live phase, and that latitude/longitude are optional for void-of-course calculations.

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 the tool's purpose: getting the Moon's phase angle, illumination, sign, and void-of-course status at a specific time. It also differentiates from sibling tools by explicitly stating what it does not do (e.g., upcoming phase dates) and pointing to alternatives.

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 provides clear guidance on when to use this tool versus alternatives, with explicit 'THIS TOOL ANSWERS' and 'THIS TOOL DOES NOT ANSWER' sections. It even mentions a credit-saving alternative for phase-only queries, making usage context very clear.

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