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

Annotations already declare readOnly, idempotent, non-destructive, and closed-world, so the safety profile is covered. The description adds real behavioral detail beyond them: a fixed seven-night horizon, a 10° altitude threshold, dark-sky-only filtering, inclusion of cloud cover, and Warsaw as the fallback location.

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 dense sentence with no filler; the object list leads, the measurement criteria follow, and the default trails at the end. The colon-and-list construction is slightly dense but every clause carries information.

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 no explanation, and annotations carry the safety profile. The description supplies the horizon, threshold, and default location; the only residual gap is that it does not resolve how lat/lon interact with city, though the schema hints at 'nearest seat'.

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 coverage is 100%, so the baseline is 3 regardless of description. The one addition is the default-location rule ('Warsaw when no place is given'), which all four parameters being optional makes genuinely useful, but the lat/lon-versus-city precedence and the lang enum are left entirely to the schema.

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 names the exact resource (Mercury, Venus, Mars, Jupiter, Saturn) and scope (next seven nights, Polish city, dark hours), plus the specific outputs (rise-above-10° time, highest point, brightness, cloud cover), so an agent knows precisely what it gets back. It never states a verb, but the content is specific enough to distinguish it from aurora_forecast, iss_passes, and meteor_showers; only tonight_sky remains an unaddressed overlap.

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 the content ('over a Polish city for the next seven nights'), and the default 'Warsaw when no place is given' removes one decision point. There is no explicit statement of when to prefer this over the sibling tonight_sky, nor any exclusion, so an agent must infer routing.

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