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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false, and openWorldHint=false, so the safety profile is fully covered. The description adds the useful behavioral nuance that this works in two modes — bare postcode (journey) or postcode plus vehicle data (exact vehicle decision) — but says nothing about result format or lookup failures for unrecognised postcodes.

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?

A single front-loaded sentence covering scope, the required postcode anchor, and the optional refinements. Nothing is padded, though it spends its one sentence on inputs rather than on the routing information an agent most needs.

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?

For a one-parameter nested-body read tool with full annotations and a fully described schema, the description covers inputs adequately. The remaining gap is sibling differentiation — the tool sits beside vehicle_check_clean_air and clean_air_zones with no stated boundary between them.

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% and each field is documented with examples, so the schema carries the load. The description correctly names vrm, euro_status, and fuel_type as optional refinements that make the decision exact, which is a small but genuine addition over the schema's per-field text.

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 clean-air-zone compliance for a vehicle or journey from a postcode — so the agent knows exactly what domain this covers. However, it does not distinguish itself from near-identical siblings such as vehicle_check_clean_air or clean_air_zones, leaving overlap unresolved.

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 says what the check is but never states when to choose it over siblings like vehicle_check_clean_air, clean_air_zones, or clean_air_catalogue. The only usage hint is that vrm/euro_status/fuel_type are optional for a more exact decision, which is parameter guidance rather than routing guidance.

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