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

Annotations already cover the safety profile: read-only, idempotent, non-destructive, and closed-world. The description adds useful behavioral context by saying the result includes zone rules and any applicable charge, though it does not describe edge cases such as missing vehicle data or non-chargeable zones.

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?

The description is two short sentences, front-loaded with the core purpose and followed by the required inputs. There is no redundant or filler text.

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 usefully states that the result includes zone rules and any charge. The input schema is fully documented, but the description does not resolve how this tool relates to clean_air_check or clarify that vrm is optional in the schema even though the description tells the caller to give it.

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 the schema already explains that vrm is a UK registration and postcode is a destination postcode. The description reinforces those meanings but adds no syntax, format, or optionality details 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?

The description states a specific verb and resource: checking whether a vehicle may enter a UK clean air zone, including London ULEZ, using registration and destination postcode. It is clear and concrete, but it does not explicitly differentiate this tool from nearby siblings such as clean_air_check 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 description makes the intended use clear enough for a vehicle-specific clean air zone check and tells the caller to provide vrm and postcode. However, it gives no explicit when-to-use guidance versus alternatives like clean_air_check, vehicle_zones, or vehicle_check_road_legal.

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