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

Annotations already cover read-only, non-destructive, and open-world nature. The description adds significant behavioral context beyond annotations: it explains the registry-scoping default, the rationale (different markets and airworthiness authorities), and the real-world impact (foreign comps not actionable substitutes). It doesn't describe pagination or return format, but the output schema likely covers that.

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 reasonably concise and front-loads the core purpose and default scoping behavior. It includes a specific example that, while helpful, adds length; overall it remains focused and every sentence contributes to understanding.

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?

Given the tool has an output schema, the description needn't explain return values. It covers the key behavioral nuance (registry scoping) and use cases thoroughly. The only minor gap is lack of guidance on the registration parameter format, but for a read-only lookup tool with clear defaults, this is acceptable.

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 provides a description for registry_scope that already covers its meaning and default, matching the description's explanation. The registration parameter is required but has no schema description, and the tool description doesn't add any syntax or format guidance for it. With 50% schema coverage, the description doesn't fully compensate, so a baseline 3 is appropriate.

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 resource (find comparable aircraft for a given tail) and scopes it to a defined cohort (same make/model and equipment profile). It also names concrete use cases (comp tables, substitute inventory), which clearly distinguishes it from siblings like lookup_aircraft, search_aircraft, or value_aircraft.

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 explicitly states the default behavior (comps stay on the anchor's own register) and provides a clear condition for overriding it (pass registry_scope="all" only when the caller genuinely wants the global fleet). It even includes a concrete example (US Robinson R44 with 14 foreign comps) to reinforce why the default matters, leaving nothing to inference.

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