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

With readOnlyHint and openWorldHint already declared, the description adds real value by disclosing the return payload — phase/illumination details, visible passes, conjunctions, 'short highlights ready to read' — and by noting that local times depend on the supplied time zone. It omits any note on edge cases (e.g. polar latitudes with no true night), which keeps it short of a 5.

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?

Two sentences, front-loaded with the core purpose ('What there is to see tonight from a place'), followed by a dense but purposeful enumeration of returned content and one usage directive. No filler, though the content list is long enough to strain a single sentence.

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?

There is no output schema, so the description must carry return-value information — and it does, listing every major output section plus 'highlights ready to read'. Combined with the read-only annotation and fully described 6-param schema, an agent has enough to call it correctly; only edge-case behavior is unaddressed.

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 every parameter (date, lang, height_m, latitude, longitude, time_zone) is already documented with types and ranges. The description only reinforces that lat/long are required and that time_zone governs local times, adding little beyond the schema — the baseline 3 for full coverage is appropriate.

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 and enumerates its contents precisely: night start/end, Moon phase and illumination, naked-eye planets, ISS/Tiangong/Hubble passes, Moon-planet pairings, and events. It is clearly an aggregate 'summary of tonight' tool, distinguishable by content from narrower siblings like perigee_passes or perigee_sky_conjunctions, though it never names those siblings.

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 clarifies which night is covered ('the coming night, or the current one') and tells the agent to supply latitude/longitude plus an IANA time zone for local times, which is useful context. However, it gives no explicit when-to-use versus alternatives (e.g. perigee_sky or perigee_passes) and no exclusions, so usage is only implied.

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