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 context beyond that: the data source (official DVSA records), the UK/Northern Ireland-only boundary, and the derived mileage-decrease check that flags potential clocking — a non-obvious analytic an agent should know it gets for free.

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-loaded with the critical constraint ('UK-registered vehicles only') and the data source before the resource detail. The trailing list of six example queries is longer than strictly necessary and slightly redundant with the body, costing a point.

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 must explain the return shape, and it does: per-test date, result, mileage, advisories, defects, failures, plus the mileage-anomaly indicator. Scope restrictions are stated, so an agent has everything needed to call it and interpret the response.

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 single 'registration' param is thoroughly documented in-schema (case/space insensitivity, GB/NI-only). The description only reinforces the UK-registration restriction, which is already in the schema, so it adds marginal value. Baseline 3 applies when the schema carries the parameter burden.

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 (get) and resource (full MOT test history) and enumerates exactly what is returned — every test with date, result, recorded mileage, advisories, minor defects and failures. That content detail is enough to distinguish it from get_mot_status (a status checker) without naming the sibling, so the agent can route correctly.

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?

Six concrete example queries ('why did it fail its MOT', 'what were the advisories', 'has it been clocked') map clearly onto when to reach for this tool, and 'UK-registered vehicles only' sets a hard scope. It stops short of naming the alternative tools (get_mot_status / lookup_vehicle) or stating when-not-to-use, so it does not reach a 5.

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