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 useful non-obvious behavior: no account or credit required, the output contains locked teasers and a verdict image, and it can pose up to three questions. It does not discuss rate limits or caching, but with annotations carrying the safety burden this is strong.

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 payload contents before the scoping and presentation notes, and every sentence carries information. The middle list of returned elements is dense but not padded; it reads as efficient rather than sprawling.

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?

Output schema exists, so return-value documentation is not required, yet the description still complements it with scope, exclusions, an auth/credit note and a rendering instruction. For a single-parameter read tool with rich annotations, an agent has everything needed to invoke it 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?

There is a single required parameter and schema description coverage is 100%; the schema already documents 'UK registration plate, any spacing or case'. The description adds no format, validation or normalization detail beyond that, so the baseline of 3 for a fully documented schema 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 names the specific resource (a UK car's free check) and enumerates exactly what it covers: identity, tax, MOT status, latest test, defects, mileage and summary flags. It also implicitly distinguishes itself from the heavier sibling by stating that next-MOT estimates, repair prices, mileage analysis and older MOT details 'require the detailed report', pointing at full_report.

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?

It defines the boundary explicitly: this tool gives the free facts plus teasers, and the deeper fields need the detailed report. It also states the entry condition ('No account or credit needed') and instructs the agent to show the returned markdown field as-is, leaving no ambiguity about when and how to use it.

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