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

Annotations already declare read-only, idempotent, non-destructive and closed-world behavior, so the safety profile is covered. The description adds genuinely useful context beyond that: the data source (latest DVSA file) and the 'Companies only' restriction, which signals that other entity types are excluded. It stops short of noting freshness or pagination limits, but the annotation bar is already met.

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 sentences, front-loaded with the core purpose and then the returned columns. Every clause earns its place; no filler or repetition of the title.

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 an output schema present, the description need not explain return values, yet it usefully enumerates the row fields. It covers both parameters' semantics and the ranking scope. The main minor gap is the absence of guidance on which mode to pick versus sibling tools, but nothing required to call it correctly is missing.

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 only 50% – the 'kind' enum carries no schema description. The description compensates by explaining what each enum value means ('haulage-companies' = Standard goods licences top 100 nationally; 'coach-and-bus-operators' = PSV licences) and by clarifying that supplying an area yields the top 50 in that traffic area. This adds meaning beyond the raw schema, though the slug/letter/name format is left to the schema.

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 and resource: ranking of companies by vehicles authorised, drawn from the latest DVSA file. It precisely delineates the two output modes ('haulage-companies' top 100 nationally vs 'coach-and-bus-operators' PSV, or top 50 in one traffic area), which distinguishes it from sibling tools like search_operators and area_stats.

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 description explains the two selection modes and the ranking scope, which implicitly guides which 'kind' to choose, but it never states when to prefer this tool over search_operators or area_stats. Usage is implied through the scope description rather than explicitly contrasted with alternatives.

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