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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the bar is lower. The description still adds real behavioral context beyond them: comparisons are normalized to 'equal units' and each figure carries 'individual sources', and it warns that 'prices are estimates' — a data-reliability caveat the agent could not derive from annotations.

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 short sentences, zero filler, with the core action and cardinality front-loaded and the caveat last. Every clause carries 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?

With no output schema, the description bears some burden for explaining what comes back, and it only gestures at this via 'individual sources'. For a 2-parameter read-only comparison tool with solid annotations, that is adequate but leaves the agent guessing at the result shape (per-model rows? per-field sources?).

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 coverage is 50% and both properties already carry descriptions (the lang enum/fallback note and the exact-slug warning), so the schema does most of the work. The description only restates the 2–4 cardinality already encoded in minItems/maxItems; 'equal units' describes comparison behavior rather than parameter meaning, so no meaningful lift over the schema.

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 (compare) and resource (aircraft models) with an explicit cardinality bound of two to four. It does not name or distinguish itself from the closest siblings (get_aircraft, search_aircraft), so the agent must infer that this is the multi-model side-by-side tool rather than a single-record lookup.

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 phrase 'exact aircraft models' implies the prerequisite that callers must already hold precise identifiers (matching the schema's exact-slug requirement) rather than guessed display names. However, it never states when to prefer this over get_aircraft or search_aircraft, and offers no exclusions or alternative routing.

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