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 discloses the tool is read-only (computes from given date) and lists return fields. However, it does not mention any limitations, auth needs, or rate limits, which is acceptable for a simple computation tool.

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?

Two sentences: first states purpose and use cases, second lists inputs/outputs and a pointer to related tools. No unnecessary words. Misses a perfect 5 due to slight redundancy ('Inputs: date' already in schema).

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 that an output schema exists (as indicated by context signals), the description does not need to detail return values. It covers purpose, use context, input, output summary, and related tools, making it complete for this simple tool.

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 date parameter, so the description adds little value beyond restating 'Inputs: date'. The description implies the date can be any date, which is a minor addition. Baseline 3 due to high schema coverage.

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 it computes moon phase and illumination for any date, listing specific use cases (astronomy, agriculture, fishing) and outputs (phase name, illumination %, age). This distinguishes it from the many sibling calculator tools, as no other moon-related tool is 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?

It provides context for when to use the tool (astronomy, agriculture, fishing) and references list_bundles for related calculators. However, it does not explicitly exclude other cases or compare to similar tools.

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