Moon Phase

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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint, and destructiveHint=false, making safety clear. The description adds that it's location-independent and requires no birth data, providing additional behavioral context. No contradictions with annotations.

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 with zero wasted words. It front-loads the main action and outputs, follows with uniqueness (location-independence), and ends with use cases. Every sentence earns its place.

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?

For a read-only lookup tool with 4 optional parameters and an output schema, the description covers purpose, inputs, uniqueness, and use cases. No critical gaps remain.

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 description coverage is 100%, so the input schema already documents each parameter's purpose. The description does not add new parameter-specific information beyond summarizing the overall functionality. It meets the baseline but does not exceed it.

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 verb 'Get' and the resource 'moon phase' with specific attributes (phase, sign, illumination, angle). It differentiates from siblings by highlighting 'Location-independent — no birth data needed', distinguishing it from tools like astral_compute_natal_chart. Use cases are explicitly listed.

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 context: 'for now or a chosen local date/time' and 'location-independent'. It lists use cases (ritual timing, journaling prompts) but does not explicitly state when not to use this tool or mention alternative siblings. Nonetheless, the context is sufficient for most scenarios.

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