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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so safety is covered. The description adds genuinely useful context the annotations don't: the POST endpoint, the required field set, and the '20 credits (Tier 2)' cost. It does not explain any rate limiting or result semantics, but with strong annotation coverage a 3 is fair.

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?

Front-loaded with the core purpose in the first sentence, followed by a compact bracketed metadata block (group, endpoint, required, cost). No filler, though the [Required: ...] line largely duplicates the schema's required array.

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?

An output schema exists, so return values need not be explained. However, the description leaves the numeric parameter formats undefined and the role of currentHour (unlisted but clearly tied to 'the exact moment') unexplained, which is a meaningful gap for an otherwise simple read-only calculation 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?

Schema description coverage is 33%: only 'fields' and 'precision' are documented. The description restates the three required params (already in the schema's required array) but gives no units or format for dayOfWeek (0-6? name?) or sunriseHour/sunsetHour (decimal hours? minutes?), and never mentions currentHour, which is schematically present and arguably essential to pin 'the exact moment'. That missing param is a real semantic gap.

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+resource: 'Return the planetary hour ruler' plus the dual scope 'at the exact moment of a horary question' and 'check if it matches the ASC ruler'. This is much clearer than the generic sibling astroway_calendar_planetary_hours, though it doesn't name that sibling explicitly to help disambiguation.

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 implies context (horary question + ASC comparison) but gives no explicit when-to-use, when-not-to-use, or alternatives. With near-identical siblings such as astroway_calendar_planetary_hours and astroway_horary_horary, the agent gets no routing guidance.

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