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

Annotations already establish read-only and idempotent behavior. The description adds meaningful context beyond this: it clarifies the legal/interpretive meaning of a register match ('does not mean the employer will sponsor a given job') and explicitly labels the output as information, not advice. This goes beyond the structured hints.

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?

Three tightly written sentences with the core action front-loaded and no wasted words; each sentence adds a distinct point: what it does, what the results mean, and a disclaimer. It is appropriately sized for the tool's complexity.

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?

For a simple read-only lookup with no output schema, the description covers what it returns (matching organisations, sponsorship routes, rating) and warns about false positives. Combined with the rich parameter descriptions in the schema and the readOnly/idempotent hints, an agent has enough 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?

Schema coverage is 100%, so the baseline is 3 and the description need not repeat parameter details. It does echo the name/town search semantics ('by organisation name (and optionally town)') without adding format or syntax details, so it adds no significant value beyond 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 (Check) and resource (Home Office register of licensed sponsors), and explicitly describes what it searches by and returns. This clearly differentiates it from siblings (going_rate, visa_cost_estimate) without needing to open their schemas.

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 makes the primary use case evident—checking whether a UK employer holds a sponsor licence—and adds an interpretive caveat about register presence. However, it does not explicitly state when to prefer this tool over siblings or when not to use it, leaving the routing inference to the agent.

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