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

The annotations already mark the tool as read-only and idempotent, but the description adds substantial behavioral nuance: timeline entries represent monthly RAB snapshots where ownership/operator changed, the first entry is a marker rather than an event, dates are observation dates rather than exact change dates, and FAA country matching requires both N-number and serial. It also discloses that natural-person names may appear while CPF numbers never will. This goes well beyond the annotations and prevents misinterpretation of returned data.

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 description is dense but every sentence earns its place: main purpose is front-loaded, followed by critical data-currency caveats and provenance constraints. Despite its length, it is efficiently structured with semicolons and parentheticals, and it avoids repeating schema or annotation content.

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 single-parameter, read-only historical tool with an output schema present, the description covers all essential contextual gaps: what timeline[] contains, how first_seen works, how dates should be interpreted, when foreignOrigin and country are populated, and privacy behavior. An agent has enough to call the tool correctly and interpret results reliably.

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 input schema has one parameter, registration, and its description fully covers format, hyphen/case flexibility, and examples. The tool description does not need to repeat those details and does not add parameter-level semantics, so the baseline of 3 is appropriate since the schema carries the full burden.

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 opens with a specific verb and resource: it returns an ownership/operator timeline for a Brazilian-registered aircraft by matricula, plus foreign-origin and accident/incident data. This clearly separates it from the many sibling lookup/fleet/registry tools, which focus on current data, searches, or aggregates.

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 description makes it obvious this is the historical-timeline tool: 'Ownership/operator timeline' is placed first and the content is framed around historical snapshots and provenance caveats. It does not explicitly name alternatives or say 'do not use for current registry data', but the context is clear enough for an agent to choose it over current-state lookup tools.

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