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

Annotations already establish readOnlyHint=true, idempotentHint=true, and openWorldHint=false, so the safety profile is covered. The description adds one genuinely useful behavioral note, 'No generated text' (pure calculation, no narrative), but says nothing about response size, whether the week's events always appear, or how missing birth time alters the result beyond the schema's own note.

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 most important content (what is returned) is front-loaded. It is slightly run-on, packing four distinct outputs plus a conditional and a caveat into one clause chain, which costs a little readability.

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?

With no output schema, the description carries the return-value burden, and it does describe the returned contents and the effect of the birth parameter, including the planet-by-planet transit orbs. It stops short of stating prerequisites or routing guidance, but for a two-parameter calculation tool it is largely sufficient.

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 50% (date and most birth fields documented, latitude/longitude not). The description compensates by clarifying the conditional role of the birth object: it activates the natal transit computation, otherwise only sky/phase/events are returned. That adds meaning beyond the schema, though it does not address the undocumented coordinate fields.

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 enumerates concrete outputs: the sky at noon UTC, the Moon's phase, the week's sky events, and, with birth data, transits to the natal chart with orb. That is a specific, verifiable content claim. It does not explicitly distinguish itself from the close siblings 'sky' and 'transits', which it appears to combine, so an agent must infer the boundary.

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?

There is no statement of when to choose this over 'sky', 'transits', 'natal_chart', or 'solar_return'. The only usage signal is the implicit conditional 'with birth data', which hints that natal transits require birth data but does not frame alternatives or exclusions.

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