calculate_moon_phase

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

No annotations are provided, so the description carries the full burden. It states the tool computes data for any date but does not disclose safety traits (e.g., read-only, no side effects). For a calculator tool, this is minimal; more context (e.g., that it's non-destructive) would help.

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 three sentences long, each serving a distinct purpose: stating function, giving use cases, and listing inputs/outputs. It is efficient with no wasted words.

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 tool has an output schema, so the description need not detail return values. It mentions outputs (phase name, illumination %, age in days) and references a related bundle. For a simple calculator, this is sufficiently complete.

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 one parameter 'date', including a pattern and description. The description repeats this but adds no new semantic detail beyond use-case context. 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 'Compute current moon phase and illumination % for any date,' specifying the action and resource. It lists inputs and outputs, distinguishing the tool from generic calculators. However, it does not explicitly differentiate from sibling tools beyond mentioning a related bundle.

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 use cases ('Use for astronomy, agriculture, fishing'), giving context for when to use the tool. It also references 'list_bundles' for related calculators, but lacks explicit guidance on when not to use this tool versus alternatives.

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