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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the description's job is to add context, and it does: it discloses the 7-day history window, the conditional live-position return ('if flying'), and that no API key or quota cost is involved. It stops short of stating lookup failure behavior for unknown idents or any rate limits.

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?

One front-loaded sentence that leads with the input, then the output payload, then the cost/access note. No filler, no restated title, every clause adds information.

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?

No output schema exists, and the description compensates by enumerating the returned fields, so an agent knows what to expect. Given a one-parameter read-only lookup this is nearly sufficient; only sibling differentiation and edge-case behavior for invalid idents are missing.

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?

The single 'ident' parameter is undocumented in the schema (0% coverage), so the description carries the burden and does: it accepts either a registration (N12345, G-EUPT) or a Mode-S hex (a1b2c3), with concrete examples of both formats. It does not state whether the ident is case-insensitive or whether a leading '~' / hex prefix is needed, leaving some ambiguity.

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?

Names a specific resource (an aircraft) and enumerates exactly what comes back: type, operator, current position if airborne, and flights in the last 7 days. It is clear what the tool does, though it never explicitly contrasts itself with siblings such as aircraft_track or flight_history that likely return overlapping data.

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 is only implied by the returned fields; there is no statement of when to prefer this over aircraft_track, flight_status, or flight_history, nor any prerequisite or exclusion. The 'Free, no key' note is a useful call-to-action hint but is not selection guidance.

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