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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, open-world), so the description is not carrying that burden. It still adds real value beyond them by naming the upstream source (DVSA) and disclosing a 10-credit cost, which matters for invocation decisions. It doesn't say what happens for an unknown or non-UK plate.

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?

Two tight sentences: the payload of returned fields is front-loaded, then use case plus cost. The field enumeration earns its place because there is no output schema, and there is no redundant restatement of the tool name.

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 compensates by listing the returned data (dates, pass/fail, expiry, mileage, defect severities), and it adds source and cost. For a one-parameter lookup this is complete enough for an agent to call correctly.

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 there is only one parameter, so the schema does the work. The description's 'UK number plate' does add a modest constraint on the expected input format beyond 'string, required: UK registration', but no spacing/format normalisation guidance.

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: full MOT test history for a UK plate, sourced from DVSA, and enumerates what the history contains. It is clearly distinct from siblings such as uk_vehicle or vehicle_recalls in substance, though it never names an alternative to contrast against.

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?

Gives a usage context ('checking a used car before buying or when the next MOT is due'), which is genuine when-to-use guidance. It stops short of explicit exclusions or pointing to neighbours like uk_mileage_check or uk_vehicle for adjacent questions.

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