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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), but the description adds value beyond them: the API key requirement on the public server and the specific key_required error behaviour with a pointer to getting a key. It doesn't mention result-count or pagination behaviour, so it stops just short of exemplary.

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 front-loaded sentences: ranking semantics first, then when to use it, then the sibling alternative and the auth caveat. No filler and no repetition of schema content.

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?

An output schema exists, so return values need no explanation, and the description covers scope, selection criteria and the key failure mode. With 9 parameters it could do slightly more to signal that ranking ignores coverage in the returned ordering, but nothing an agent needs to call it correctly is missing.

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 78% across 9 parameters, so the schema does most of the work and the baseline is 3. The description only indirectly touches parameters ('one insurer's prices' hints at insurers, 'ranked by annual premium' frames the limit/one_per_product defaults) and adds no format or syntax detail.

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 and resource with scope: 'Every matching plan ranked by annual premium alone, with no view on coverage.' It explicitly contrasts itself with find_plans, so an agent can distinguish it from the sibling 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?

Names concrete triggers ('asks for the cheapest, for a full list, or for one insurer's prices') and the exclusion condition ('When what the plan covers matters, use find_plans'). The routing decision is fully spelled out.

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