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

Annotations already establish readOnly, idempotent, non-destructive and open-world semantics, so the safety profile is covered. The description goes well beyond them by disclosing the matching rules (organisation name as the register spells it, company number pulling registered and former names, town cross-checked against the registered office) and the temporal scope of results, including former licences and recorded changes since 6 October 2026. It stops short of stating rate limits or result-size behaviour.

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?

It is a single dense sentence-complex, but the core question (is this organisation on the register, on which routes, at what rating) leads, and the matching and coverage caveats follow. Every clause carries information; slightly dense for the reader but not padded.

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 carries the burden of describing returns, and it does: current licences, former licences with exit dates, and recorded changes. Combined with the 100%-covered single parameter and the annotation safety profile, an agent has enough to call it correctly, though nothing tells it when another register-check sibling would be the better choice.

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 the schema already says 'company number or organisation name', so the baseline is 3. The description earns above baseline by explaining the consequences of each input form: a company number resolves registered and former names, whereas a name must match the register's spelling, and the town is validated against the registered office.

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 states a precise verb+resource: checking whether an organisation appears on the register of licensed sponsors (workers), and it adds the dimensions of the result (which routes, what rating). That is specific enough to separate it from other regulatory-check siblings like sra_check, cqc_check or charity_check without opening a 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?

Usage is implied by the register being named, but there is no explicit when-to-use/when-not guidance and no alternative tool is named (e.g. when to prefer company_search or another register check). An agent can infer the purpose but receives no routing advice.

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