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

Annotations already declare readOnly/idempotent/non-destructive/openWorld=false, so the safety profile is covered. The description adds genuinely useful behavior beyond that: the data is a point-in-time snapshot tied to the register date, results are ranked largest-fleet-first, totals are grouped by traffic area, and the output is not an insolvency signal. It stops short of describing pagination or refresh cadence.

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?

Four short sentences, front-loaded with the resource and scope, followed by the optional filter and the interpretive caveat. No filler; the 'Companies only' fragment carries real filtering information.

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, return-value explanation is unnecessary, and the description still covers scope, ordering, aggregation and the key interpretive caveat. The remaining gap is the undocumented 'limit' parameter and any statement of data freshness or result-size behavior.

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 50%: 'area' is documented in the schema (slug/letter/name), and the description adds that it is optional and restricted to a single area. 'limit' has no description in either place, though 'largest fleets first' implicitly tells the agent the ordering that limit truncates. The description compensates only partially for the coverage gap.

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 resource and scope: companies holding operator licences with accounts overdue at the Companies House register date, sorted largest fleets first, with totals by traffic area. It also explicitly separates itself from the insolvency_watch sibling ('A filing fact, not a sign of insolvency'), so an agent can distinguish the two without opening either schema.

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 clear context for when the tool applies (filing-overdue research, optionally narrowed to one traffic area) and implicitly excludes the insolvency use case. It does not, however, name an explicit alternative to reach for or spell out a when-not-to-use condition beyond the caveat sentence.

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