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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and closed-world, so the safety profile is covered. The description adds genuine operational context beyond that: the 20-credit Tier 2 cost and the Horary grouping. It says nothing about what the comparison result contains or how sunrise/sunset inputs shape the hour boundaries.

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 short, front-loaded lines with no filler; the core action leads and the metadata tags trail. Slightly more compact than necessary given the bracket lines, but nothing is wasted.

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 tool with 6 parameters at 33% schema coverage, an output schema, and no explanation of the required sunrise/sunset/hour inputs, the description is too thin. An agent can grasp the intent but not how to populate three required numeric fields or what the matching flag means.

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 only 33% (6 params, only 'fields' and 'precision' documented). The description adds no meaning for dayOfWeek, sunriseHour, sunsetHour or currentHour — notably it never explains the encoding of dayOfWeek or the expected units/format of the hour values, which is exactly what the schema omits.

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?

States a specific verb and resource: it returns the planetary hour ruler at the moment of a horary question and compares it to the ASC ruler. That is concrete and actionable. It does not, however, differentiate itself from the close sibling astroway_calendar_planetary_hours, so an agent cannot tell from the text which one to pick.

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 phrase 'at the exact moment of a horary question' implies the horary context in which this tool belongs, which is useful implied guidance. There is no explicit when-to-use/when-not statement and no reference to the calendar planetary-hours sibling, so routing remains partly inferential.

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