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

Annotations already declare readOnly/idempotent/non-destructive, so the safety profile is covered; the description adds real behavior: the result is a link that opens the sky map, printing supports A4/A3/A6, and the answer additionally lists eclipses within 15 days, active meteor showers, and the NASA picture of the day. Some of that overlaps the output schema, and it says nothing about the link's lifetime or failure modes when a place is not found.

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 purpose is front-loaded, but the core is a single sprawling run-on sentence that strings together card contents, print formats, and every returned fact. The information earns its place, yet the structure makes it hard to scan and would benefit from being split into purpose, inputs, and outputs.

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 12-parameter tool with an output schema and read-only annotations, the description covers the important agent-facing facts: default time, place vs coordinates, print formats, and the extra returned data. The remaining gaps are minor edge cases (place not found, conflicting place and coordinates) that the schema partially handles.

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, but the description adds genuine meaning beyond the schema: it clarifies the default hour as 22:00 when no time is given ('at the given hour, or 22:00'), and explains that title/subtitle map to the card's heading and its line. It does not address precedence when both place and lat/lon are supplied.

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?

States a specific verb and artifact: it 'makes a printable card of the sky on a day' at a place, and enumerates what the card and answer contain (title, Moon phase, sunrise/sunset, planets, QR code, A4/A3/A6 formats). That is clearly distinguishable from data-returning siblings like sky_at or astro_calendar, which do not produce a card.

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?

Ends with an explicit usage condition: 'Use it when someone wants a gift or keepsake of the night sky on a date,' which tells the agent the intent that selects this tool. It stops short of naming an alternative (e.g. use sky_at for raw sky data instead of a card), so the routing is implied rather than fully spelled out.

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