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

Annotations already establish the safety profile (readOnly, idempotent, non-destructive, closed-world). The description adds useful return context ('the zone rules and any charge that applies') and geographic scope, but says nothing about failure modes (unknown VRM, non-UK postcode) or what the charge figures represent, so it is adequate rather than rich.

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 sentences, front-loaded with the purpose and ending with the inputs; nothing is padded. The second sentence is close to redundant with the schema, which keeps it short of a perfect score.

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 correctly sketches what comes back (zone rules and applicable charge) for a one-parameter check. It is still thin on how to interpret or act on the result and gives no routing against the several overlapping clean-air/vehicle siblings.

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 100%, so the nested body, vrm, and postcode fields are already documented with examples in the schema. The description's 'vrm for the vehicle and postcode for where it is going' restates the schema (notably that postcode is the destination) but adds no format, syntax, or validation detail beyond it.

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 ('Check whether a vehicle may enter a UK clean air zone') plus the inputs and scope (UK, including London ULEZ), so an agent knows exactly what it does. It does not, however, distinguish itself from near-identical siblings such as clean_air_check, vehicle_check_road_legal, or vehicle_zones.

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 only directive is 'Give vrm for the vehicle and postcode for where it is going', which is parameter filling rather than when-to-use guidance. No alternative (clean_air_check, vehicle_check_road_legal, vehicle_zones) is named, and no condition or exclusion tells the agent when this tool is the right pick.

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