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

Annotations already mark the tool read-only and non-destructive, and the description adds valuable context: it restricts to UK-registered vehicles, identifies the official DVSA data source, and discloses the derived mileage-decrease signal that can indicate clocking or error. This goes beyond the structured annotations and is genuinely useful.

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 well-structured and economical: it front-loads scope and data source, then explains the returned content and the extra mileage-consistency signal, and ends with concrete example queries. Every sentence earns its place with no filler.

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?

Although there is no output schema, the description enumerates what each returned test record contains and covers a wide range of likely user intents. For a single-parameter, read-only tool, this provides enough context for an agent to invoke it correctly without missing critical information.

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?

The input schema already fully describes the registration parameter, including case/spacing normalization and Great Britain/Northern Ireland limitations. The description reinforces the UK-only scope but does not add substantial parameter-level meaning beyond the schema, so the baseline score of 3 is appropriate.

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 operation: retrieving the full MOT test history for a UK vehicle, and enumerates what is included (date, result, mileage, advisories, minor defects, failures). This clearly distinguishes it from sibling tools by emphasizing historical test records rather than current status or general vehicle lookup.

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 gives explicit user-intent examples such as 'why did it fail its MOT', 'what were the advisories', 'has it been clocked', and 'is the mileage consistent', which tell an agent when to invoke the tool. It does not explicitly name siblings or state when not to use it, so it stops short of a full alternative-routing explanation.

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