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

Annotations already cover read-only and open-world behavior, so the description's added value is in the precision and output-shape disclosure: timing 'to a fraction of a second', relative velocity only for two Earth satellites, and a hard warning that public orbits are unsuitable for collision avoidance with the response itself carrying that disclaimer. That is meaningful context beyond the annotations, though it says nothing about failure modes for non-satellite or non-Earth object pairs.

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 compact two-sentence definition that front-loads what is computed and what is returned before the caveat. The trailing 'and the answer says so' is slightly awkward but does convey a real behavioral fact rather than padding.

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 six parameters, no output schema, and a numerically sensitive computation, the description does the important work: it names the three returned quantities, bounds the time window, and flags the accuracy limitation. What is missing is only the treatment of edge cases (e.g., objects that never approach, non-Earth objects), which is minor given full schema coverage.

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 all six parameters (from, to, days, start, time_zone, lang) are already documented structurally. The description's '(default 1 day, at most 1)' merely restates the days parameter's schema default and maximum, adding no new syntax or interpretation guidance.

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 uses a specific verb+resource framing — the minimum distance between two objects over a time window — and lists the returned quantities (time of closest approach, distance, relative velocity). It is clearly a closest-approach computation rather than an instantaneous distance, but it never names the sibling tools (perigee_distance, perigee_distance_series) it is distinguished from.

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 context is implied by 'over a period (default 1 day, at most 1)' and by the education-only caveat, which tells the agent the precision regime this tool operates in. However, there is no explicit 'use this instead of X when Y' guidance against the many distance/orbit siblings, so selection still requires inference.

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