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

With readOnlyHint=true and openWorldHint=false already covering safety and locality, the description contributes substantial behavioral context by enumerating what is returned: day/twilight/night, Sun rise/set, Moon phase and illumination, planets with altitude/direction/magnitude/constellation/visibility, and bright stars. It does not discuss errors or edge cases, but for a read-only query this is above the annotation baseline.

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?

The definition is front-loaded with the core question and then packs the return contents into one dense but purposeful list. The final sentence is a direct usage cue, and no sentence 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?

Because there is no output schema, the description carries the burden of explaining return values, and it does so comprehensively across the sky objects and conditions. Together with the fully documented input schema and read-only annotation, an agent has enough to invoke the tool correctly.

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%, so latitude, longitude, date, time_zone, height_m and lang are already documented. The description adds only the default-now behavior and the evening-time usage hint, which is useful but not much beyond 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 resource precisely—sky conditions from a place at a date—and enumerates the Sun, Moon, planets and bright stars it reports. It is clear enough to distinguish from general event or orbit tools, but it does not explicitly differentiate itself from sibling perigee_tonight despite using the overlapping phrase 'what can I see tonight.'

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?

It gives a concrete usage hint: for 'what can I see tonight', supply the evening time. However, it does not state when not to use this tool or name an alternative such as perigee_tonight, so the agent must infer the boundary from the sibling list.

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