lookup_plateOne UK car's MOT history from the DVSA by its registration: each test with its result, mileage and defects or advisories, whether its MOT is valid, warnings (mileage going down, gaps with no MOT, an outstanding safety recall) and its model's reliability grade.
| Name | Required | Description | Default |
|---|---|---|---|
| registration | Yes | UK number plate, e.g. AB12 CDE. |
Changes observed during successful MCP inspections.
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is covered. The description adds real substance beyond that by enumerating the returned payload (per-test result, mileage, defects/advisories, validity, warnings, reliability grade) and naming the upstream source, DVSA. It does not mention error behaviour for unknown plates or rate limits.
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 dense sentence, front-loaded with the core action and resource, with the return payload following in a natural colon-list. No filler, though the length pushes the edge of what a single sentence can carry readably.
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 carry the return-value story — and it does, listing tests, results, mileage, defects, validity, warnings and reliability grade. Missing only edge-case behaviour (no data for a plate, invalid formats) for full completeness.
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?
With a single parameter at 100% schema coverage, the schema already documents the registration format and example. The description's 'by its registration' and 'UK car' add country/entity framing but no format, normalization or validation detail beyond what the schema states.
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?
Names a specific verb+resource+scope: MOT history for one UK car, looked up by registration, sourced from the DVSA. It is clearly distinguishable from search_cars (finding cars) and the reliability siblings (which the description treats as a field of this result rather than a separate lookup), though it never names those alternatives explicitly.
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?
Usage is implied by 'by its registration' and 'One UK car' — the singular, plate-keyed framing signals a per-vehicle lookup. There is no explicit when-to-use/when-not guidance or statement of what to call instead when the plate is unknown or a broader search is wanted.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
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