check_sponsor

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

Annotations already cover the read-only, closed-world safety profile, and the description adds real behavioral value: the four possible verdicts (licensed, licensed_other_routes, possible_match, not_found), the fact that register entries carry routes and A/B ratings, and that caveats are returned. It omits timing/rate-limit behavior but is otherwise informative.

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 purpose sentence followed by clearly labeled Args and Returns blocks, with no filler. The route example list is the longest element but is directly actionable, so little is wasted.

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 fully compensates by enumerating the verdict values and the returned register data plus caveats. An agent has enough to select and call the tool and to interpret the response 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 0%, so the description carries the full burden and mostly does: it clarifies company should be the name as it appears in a job ad (legal or trading name) and gives concrete route values plus the default. It does not state matching/fuzzy-matching tolerance or name-normalization expectations, which matters for a lookup tool.

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+resource+scope: checking whether a UK employer is licensed to sponsor visas on a given route. The verdict taxonomy in the Returns block makes it clearly a point-lookup tool, distinct from the sibling search_sponsors bulk-search tool.

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 rather than stated: an agent can infer this is the single-employer verification call and search_sponsors is the discovery call, but neither the alternative nor the conditions selecting it are named. No when-not guidance or prerequisites are given.

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