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

Annotations already declare readOnlyHint, idempotentHint and non-destructive behaviour, so the description is not burdened with the safety profile. It adds genuine context beyond them: holder names are never sole-trader or partner names (a data/privacy caveat), and stale licences are surfaced with in_current_file: false rather than omitted.

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 core purpose in the first clause, then a dense but purposeful enumeration of contents. It is one long run-on sentence without formatting, but essentially every clause carries 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?

Given one fully documented parameter, a rich output schema and full annotation coverage, the description is nearly complete; the only missing piece is error behaviour when a licence number does not exist (vs. the disclosed in_current_file: false case). Enumerating return fields is partly redundant with the output schema but still useful as a summary.

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 parameter already documents the OB/P prefix and traffic-area encoding in the schema. The description only restates 'by its number' and adds no format, validation or edge-case detail beyond it, so the baseline of 3 applies.

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 (one GB operator licence) and the lookup key ('by its number'), which distinguishes it from the list/search siblings like search_operators, licences_ended and biggest_operators. The enumerated field list further pins down exactly what kind of record this is.

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?

Usage is only implied: the phrase 'by its number' signals a single-record lookup, so an agent can infer it should not be used for browsing. However, no sibling is named as an alternative and there is no when-to-use/when-not statement.

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