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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so the safety profile is covered. The description adds genuinely useful context — that vrm, euro_status and fuel_type are there to 'make the decision exact', implying a fallback path between registration-based and emissions-based lookups. It does not explain what a non-compliant result means or whether charges are returned.

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?

One sentence, front-loaded with the outcome (compliant or not) and the required input (postcode), then the optional refiners. Efficient, though the trailing clause is slightly compressed.

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?

There is no output schema, so the description should indicate what a check returns — a boolean, a charge band, zone names — and it does not. With a nested body object and three optional discriminators, an agent can invoke it but cannot anticipate the result shape.

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 explains the vrm/postcode/euro_status/fuel_type roles, including the 'sent when there is no registration' fallback. The description names the same three optional fields and frames their purpose, adding modest value but no syntax or format detail beyond 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 (check) and resource (UK clean air zone compliance) with the key inputs named. However, siblings such as vehicle_check_clean_air and clean_air_zones sound nearly identical, and the description does nothing to distinguish this tool from them.

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 never says when to call this rather than clean_air_zones, clean_air_catalogue, or vehicle_check_clean_air, nor does it give prerequisites or exclusions. Usage is only inferable from the tool name.

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