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

Annotations already declare readOnlyHint, idempotentHint and a closed world, so safety and repeat-call behavior are covered. The description adds only the default-date behavior, which is genuinely useful but is also echoed in the schema; nothing about return volume or coverage window beyond 'coming week' is disclosed.

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?

A single front-loaded sentence that leads with the payload and ends with the argument syntax and default. No filler, nothing redundant.

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 one-optional-parameter, read-only lookup with no output schema, the description conveys both what comes back and the default date behavior, which is enough to call it correctly. A brief note on the time basis of the 'coming week' window would make it fully 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?

Schema description coverage is 100% and the single date parameter is already documented as YYYY-MM-DD with a today (UTC) default. The description restates the same format and default, adding no new semantic detail, so the baseline of 3 applies.

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?

Names the concrete outputs (planetary positions, Moon phase, week's sky events) scoped to a single date, which is far more informative than the terse name 'sky'. It does not explicitly contrast itself with siblings like transits or daily_transits, which could plausibly overlap, so it stops short of a 5.

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?

Usage is implied by 'for a date ... today by default', which tells the agent the natural calling context. There is no explicit statement of when to prefer this over transits/daily_transits/natal_chart, and no exclusions, so it remains implied rather than stated.

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