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

Annotations already cover readOnly, idempotent, openWorld and non-destructive, so the safety profile is handled. The description adds genuinely non-obvious context beyond that: DVSA is the authoritative source, coverage is UK (GB/NI) only, and the special sentinel status first_mot_not_due carries a non-intuitive meaning for expiry_date. That domain-specific caveat is exactly the kind of value annotations cannot express.

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?

Front-loads the hard constraint ('UK-registered vehicles only') and then flows into return values before the example queries. The long quoted-query list is somewhat padded, but each phrase maps to a distinct intent, so it largely earns its place.

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 must explain what comes back — and it does: status, expiry date, days remaining, and last-test result, mileage, advisories and defects. Combined with the sentinel-status explanation and UK-only scope, an agent has everything needed to call and interpret this tool.

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 single registration parameter is fully documented in the schema, including case/space normalization and GB/NI scoping. The description restates the UK-only constraint but adds no new syntax or format detail. Baseline 3 is appropriate when the schema already carries the parameter semantics.

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+resource: the current MOT status of a UK car, van or motorbike, plus expiry date, days remaining, and last-test result. It enumerates the returned fields precisely, which implicitly separates it from get_mot_history (full past tests) and lookup_vehicle (vehicle attributes). An agent can distinguish it from its siblings without opening any schema.

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 trailing queries ('when is my MOT due', 'has my MOT expired', 'did it pass its last MOT') give concrete triggering conditions that map to real user phrasing. It also scopes the tool to UK-registered vehicles only. It stops short of explicitly naming when to prefer get_mot_history or lookup_vehicle instead, so it lands at a strong 4 rather than 5.

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