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

Annotations already cover read-only, idempotent, non-destructive and open-world traits, so the bar is lower; the description still adds useful non-structured context: the NHTSA Recalls API as source, a stated cost of 1 credit, and a scope limitation about vehicle-specific repair status. It doesn't address behavior on an unknown or malformed campaign number, which is the main remaining gap.

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?

Front-loaded with the core action and return payload, then constraints. The audience list ('For owners, journalists, lawyers and fleet managers') is the least load-bearing sentence but is short enough not to hurt.

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 carries the return-value burden and does so by enumerating the fields returned, plus source, credit cost and one scope caveat. Only error/not-found behavior and confirmation of whether coverage is US-only are left unaddressed.

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 100% and the schema already supplies both example formats ('20V314000 or 20V-314'), so the description's 'as printed on a US recall letter' adds only marginal provenance context. Baseline 3 applies when the schema does the heavy lifting on a single documented parameter.

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 ('Look up one recall by its NHTSA campaign number') plus the exact payload returned (defect, risk, remedy, affected count, makes/models/years), which distinguishes it from the sibling list-style tools vehicle_recalls and product_recalls. The example campaign number anchors the identifier format immediately.

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?

Clear context: single-record lookup keyed by a campaign number from a US recall letter, aimed at owners, journalists, lawyers and fleet managers, with an explicit exclusion ('It does not say whether a specific vehicle has been repaired'). It stops short of naming a sibling like vehicle_recalls as the search/browse alternative, so the routing is implied rather than spelled out.

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