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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), yet the description adds genuinely useful behavioral context: unknown vehicles return database suggestions, unrated vehicles stay explicitly unrated, and counts reflect source coverage rather than ground truth. The tier-based per-call limit is a valuable operational constraint not present in the schema.

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?

Three sentences, front-loaded with the core action and followed by return-behavior caveats and limits. Dense but each sentence carries information; no filler or restatement of the title.

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 does the work of describing return semantics (factual orderings, suggestions for unknown vehicles, explicit unrated status) and the tier limits. It stops short of describing result shape or ordering details, but it is sufficient for an agent to call the tool correctly.

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 0%, so structured fields carry no per-parameter meaning. The description clarifies that the input is a set of vehicles and that per-call counts are capped (2 free / 5 paid), but it never explains the required make/model/year triple or the 2000–2027 year window, leaving the schema to define the shape on its own.

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 names a specific verb and resource ('Compare recorded facts for several vehicles side by side') and delineates scope with concrete dimensions (complaints, recalls, verified complaints-per-100k-sold rates). It also explicitly excludes framing ('no recommendation, verdict or safety ranking'), which separates it from the risk-oriented sibling vehicle_risk.

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 context is clear — comparing several vehicles in one call — and hard constraints are stated (free tier up to 2, paid up to 5). It does not explicitly say when to reach for vehicle_risk or recall_changes instead, so the routing guidance against siblings is inferred rather than stated.

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