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

Annotations already establish readOnlyHint=true and openWorldHint=false, so safety and locality are covered structurally. The description adds genuinely new context beyond that: the target audience and depth (secondary-school level), which tells the agent the tone and granularity of the answers. It does not describe result shape or coverage limits (e.g. how many terms exist), so it is useful but not rich.

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 compact sentences with the scope and examples front-loaded and the fallback behavior placed last where it belongs. The trailing ellipsis after "phase…" is slightly loose but signals non-exhaustive coverage economically.

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 zero-required-parameter, read-only glossary lookup with no output schema, the description supplies the essential missing pieces: what terms are covered and what happens when term is omitted. Only the language option goes unmentioned, and the schema handles that adequately.

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%, and the schema already documents both the term examples and the omit-to-list-all behavior, so the description largely restates it. The lang parameter and its en/fr enum are never mentioned in the description, so no value is added beyond the structured data.

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 resource (student-level definitions of Perigee orbital terms) and enumerates the covered vocabulary (NORAD, COSPAR, apogee/perigee, inclination, etc.), so an agent immediately knows this is a glossary tool rather than a computation tool. It does not explicitly contrast itself with perigee_about, the nearest sibling, which keeps it short of a 5.

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?

The final clause "Without a term, lists them all" gives the one real usage decision (call with a term to define it, omit to enumerate). There is no guidance on when to prefer this over perigee_about or other explanatory siblings, so the routing signal is only implied.

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